Clinical UM Guideline

This document addresses the use of external (nonimplanted) ambulatory event monitors (AEMs) that are not equipped for real-time physician notification. Examples of devices addressed in this document include continuous 24- to 48-hour Holter monitors.

Note: This document does not address implantable ambulatory event monitors or the use of AEMs equipped with cellular telecommunications equipment for real time physician notification. For criteria related to implantable ambulatory event monitors, please refer to the applicable guidelines used by the plan.

Note: This document does not address attended, real-time electrocardiogram monitoring.

Note: For a high-level overview of this document, please see “Summary for Members and Families” below.

I.  Ambulatory Electrocardiograph (ECG) Holter Monitor

Medically Necessary:

Continuous 24- to 48-hour ambulatory ECG Holter monitor use is considered medically necessary for adults with any of the following indications:

1. As a diagnostic tool to evaluate frequent, unexplained symptoms suggestive of cardiac arrhythmias such as palpitations, unexplained dizziness or syncope or near syncope; or
2. Evaluation of hypertrophic cardiomyopathy or dilated cardiomyopathies; or
3. As a diagnostic tool for detecting ventricular arrhythmias, QT interval changes, or ST changes, to evaluate risk; or
4. As a method to assess treatment response to antiarrhythmic therapy (efficacy; proarrhythmic effect); or
5. As a method to assess for paroxysmal atrial fibrillation following cryptogenic stroke; or
6. As a method to assess for asymptomatic atrial fibrillation three or more months after ablation of arrhythmogenic foci for atrial fibrillation; or
7. Assessment of the function of pacemakers or implantable cardioverter defibrillators (ICD) in individuals:
   1. With frequent symptoms of palpitation, syncope, or near syncope to assess device function to exclude myopotential inhibition and pacemaker mediated tachycardia; or
   2. To assist in programming parameters such as rate-responsivity and automatic mode switching; or
   3. To evaluate suspected component failure or malfunction when device interrogation is not definitive; or
   4. To assess response to adjunctive pharmacologic therapy in individuals receiving frequent ICD therapy;
      or
8. Suspected variant angina.

Continuous 24- to 48-hour ambulatory ECG Holter monitor use is considered medically necessary for children with any of the following indications:

1. As a diagnostic tool to evaluate frequent, unexplained symptoms suggestive of cardiac arrhythmias such as palpitations, unexplained dizziness or syncope or near syncope; or
2. Evaluation of hypertrophic cardiomyopathy or dilated cardiomyopathies; or
3. Evaluation of possible or documented long QT syndromes; or
4. As a method to assess treatment response to antiarrhythmic therapy (efficacy; proarrhythmic effect); or
5. Palpitations in children with prior surgery for congenital heart disease and significant residual hemodynamic abnormalities; or
6. Asymptomatic, unpaced, congenital complete atrioventricular (AV) block; or
7. Evaluation of cardiac rhythm after transient AV block associated with heart surgery or catheter ablation; or
8. Evaluation of rate-responsive or physiological pacing function in children with persistent or recurrent cardiac symptoms.

Not Medically Necessary:

Ambulatory ECG Holter monitor use is considered not medically necessary when the above criteria are not met.

Ambulatory ECG Holter monitor use is considered not medically necessary for all other indications including, but not limited to:

1. Autonomic cardiac neuropathy associated with diabetes mellitus
2. After a myocardial infarction when the individual has left ventricular dysfunction (ejection fraction [EF] less than or equal to 40%).

II.  External Ambulatory Event Monitor

Medically Necessary:

The use of external ambulatory event monitors is considered medically necessary when either of the following criteria are met (A, B, or C):

1. As a diagnostic alternative to Holter monitoring, in individuals who experience infrequent symptoms (less frequently than once every 48 hours) suggestive of cardiac arrhythmias; or
2. Following cryptogenic stroke, for the detection of suspected paroxysmal atrial fibrillation when prior testing with Holter monitoring has yielded inconclusive results and when external ambulatory event monitoring is intended to guide medical management with anticoagulants; or
3. Arrhythmia monitoring after stroke when any of the following criteria are met (1, 2, or 3):
   1. For consideration of cessation of anticoagulation or other treatment decisions that depend on arrhythmia detection; or
   2. To assess the need for anticoagulation in individuals with atrial fibrillation events greater than or equal to 5 minutes based upon their estimated risk of stroke (See Discussion section); or
   3. For 2-4 weeks after a stroke when both of the following criteria are met:
      1. Anticoagulation therapy would be considered appropriate if atrial fibrillation is detected; and
      2. Either of the following criteria are met:
         1. The individual has experienced an embolic stroke presumed to be due to large or small vessel disease; or
         2. The individual has experienced an ischemic stroke of indeterminate cause.

Not Medically Necessary:

Other uses of external ambulatory event monitors and telemetry are considered not medically necessary including, but not limited to, the following clinical situations:

1. Monitoring effectiveness of antiarrhythmic therapy and detection of myocardial ischemia by detecting ST segment changes
2. Following catheter or surgical ablation of atrial fibrillation
3. Monitoring for the presence of atrial fibrillation in individuals with cryptogenic stroke when the criteria are not met.

This document describes clinical studies and expert recommendations, and explains when the use of a heart monitor worn outside of the body may be appropriate. The following summary does not replace the medical necessity criteria or other information in this document. The summary may not contain all of the relevant criteria or information. This summary is not medical advice. Please check with your healthcare provider for any advice about your health.

Key Information

External heart monitors such as Holter monitors and ambulatory event monitors (AEMs) are tools used to detect abnormal heart rhythms (arrhythmias). They include a small device worn on a strap, harness, or temporarily adhered to the body, electrical wires connect the device to sensors temporarily glued to different areas of the chest. Holter monitors record heart activity continuously for 24 to 48 hours, while ambulatory event monitors can be used for longer periods and are either triggered automatically or by the user when symptoms occur. These devices help detect conditions such as atrial fibrillation, fainting, dizziness, or palpitations. Holter monitors are best for people who have frequent symptoms, ambulatory event monitors are more helpful when symptoms happen less often. Both tools have advantages and disadvantages, depending on how often symptoms occur and what condition is being investigated. Some tests have not been studied enough to show whether they improve health.

What the Studies Show

Holter monitors are useful for checking frequent symptoms that could be due to an abnormal heart rhythm. Heart health experts recommend them for identifying arrhythmias in both adults and children. However, they may miss abnormal rhythms that happen only occasionally. Studies show that using ambulatory event monitors or longer-term monitoring can help find a specific abnormal rhythm called atrial fibrillation, that standard Holter tests might miss, especially after a stroke with no known cause. For example, a 30-day ambulatory event monitor was much better at finding atrial fibrillation than a 24-hour Holter monitor. Several studies support longer monitoring when doctors need to decide whether to start medications such as blood thinners. While finding more cases of atrial fibrillation is helpful, better studies are needed to know if this leads to fewer strokes or better health results. Experts recommend choosing a monitoring device based on how often symptoms happen and what health issues are present. There are also concerns about using these tools in ways not supported by evidence. For example, Holter monitors are not helpful for some types of diabetes-related heart problems or after a heart attack if certain heart function levels are low.

When is Holter or Ambulatory Monitoring Clinically Appropriate?

Holter monitors (24- to 48-hour recording) may be appropriate in these situations:

• For adults or children with symptoms like palpitations (a fast-beating, fluttering, or pounding heart), dizziness, or fainting that could be caused by arrhythmias.
• To evaluate certain heart conditions such as hypertrophic or dilated cardiomyopathy (thick or enlarged heart muscles).
• To monitor how well heart rhythm medications are working.
• To detect atrial fibrillation after a stroke when the cause is unclear.
• To assess pacemaker or defibrillator function in people with certain symptoms or device concerns.

External ambulatory event monitors may be appropriate in these situations:

• For people with symptoms that happen less often than every 2 days.
• After a stroke with no known cause, when a previous Holter test did not provide clear answers and doctors are deciding whether to prescribe anticoagulants.
• If the results affect treatment decisions, for example, if doctors are deciding whether to stop blood thinners (anticoagulation) or make other changes to treatment based on whether an abnormal heart rhythm is found.
• The person has had episodes of atrial fibrillation lasting 5 minutes or longer, and doctors need more information to decide whether blood thinners are needed based on the person’s overall stroke risk.
• Monitoring is done for 2 to 4 weeks after a stroke, when:
  • The person would be a candidate for blood thinners if atrial fibrillation is found; and
  • The stroke was either:
    • Thought to be caused by a clot from a large or small blood vessel, or
    • An ischemic stroke (caused by a blocked blood vessel) with no clearly identified cause.

In short, heart rhythm monitoring after a stroke is used when finding (or not finding) atrial fibrillation would change how the person is treated,  especially regarding the use of blood thinners to prevent another stroke.

When is this Not Clinically Appropriate?

Holter monitors or ambulatory event monitors are not considered appropriate when the situations listed above are not met. Specifically:

• Holter monitors are not appropriate for monitoring diabetic nerve damage affecting the heart or in people who recently had a heart attack with low heart function.
• Ambulatory event monitors are not appropriate for checking whether rhythm medications are working, for detecting chest pain from reduced blood flow, or for general atrial fibrillation screening after ablation or stroke unless criteria are met.

These tests are not clinically appropriate in other scenarios because studies have not shown they help improve health. Unnecessary or unproven tests can lead to inappropriate care.

(Return to Description)

The following codes for treatments and procedures applicable to this document are included below for informational purposes. Inclusion or exclusion of a procedure, diagnosis or device code(s) does not constitute or imply member coverage or provider reimbursement policy. Please refer to the member's contract benefits in effect at the time of service to determine coverage or non-coverage of these services as it applies to an individual member.

Ambulatory ECG Holter Monitor
When services may be Medically Necessary when criteria are met:

When services are Not Medically Necessary:
For the procedure codes listed above when criteria are not met or for all other diagnoses not listed.

External Ambulatory Event Monitor
When services may be Medically Necessary when criteria are met:

When services are Not Medically Necessary:
For the procedure codes listed above when criteria are not met or for situations designated in the Clinical Indications section as not medically necessary.

Summary

This guideline addresses the use of external ambulatory event monitors (AEMs), specifically nonimplanted devices such as 24- to 48-hour Holter monitors and longer-duration external AEMs. These devices are used for rhythm assessment in individuals with symptoms or clinical conditions suggestive of arrhythmia, including palpitations, syncope, cardiomyopathies, and post-stroke atrial fibrillation (AF) detection. The evidence base includes randomized controlled trials (RCTs) and systematic reviews showing that prolonged or event-triggered external monitoring improves arrhythmia and atrial fibrillation detection compared with standard Holter monitoring, particularly in individuals with cryptogenic stroke or high CHA₂DS₂-VASc scores.

Professional guidance cited includes recommendations from multiple societies, including:

• American College of Cardiology (ACC)/American Heart Association (AHA)/Heart Rhythm Society (HRS), guidelines for arrhythmia management, bradycardia, syncope, ventricular arrhythmias, and atrial fibrillation (2014-2023) supporting use of ambulatory ECG monitoring and selecting device type based on symptom frequency.
• European Society of Cardiology (ESC) and European Heart Rhythm Association (EHRA) guidance recommending short- and extended-term ECG monitoring for stroke evaluation and AF diagnosis.
• American Academy of Neurology (AAN) (2022) guidance suggesting prolonged cardiac rhythm monitoring (≥ 1 week) after cryptogenic stroke to identify occult AF.
• American Academy of Pediatrics (AAP) (2021) position statement on sudden cardiac death prevention noting AEMs are not routinely indicated for family screening but may be used when arrhythmia is suspected.
• The 2024 ACC Expert Consensus Pathway on arrhythmia monitoring after stroke emphasizes 2-4 week monitoring when anticoagulation decisions depend on AF detection.

Overall, evidence and consensus guidelines support external ambulatory monitoring as a diagnostic tool tailored to symptom frequency and clinical context, particularly for AF detection in high-risk or post-stroke populations.

Discussion

Arrhythmias are deviations from the normal cadence of the heartbeat which cause the heart to pump improperly. More than four million Americans have arrhythmias, most of which pose no significant health threat. As people age, the probability of experiencing an arrhythmia increases. In the United States, arrhythmias are the primary cause of sudden cardiac death, accounting for more than 350,000 deaths each year. The standard initial measure for a diagnosis of arrhythmias involves the use of electrocardiogram (ECG) testing, which allows evaluation of the electrical function of the heart.

Types of Devices

Holter monitors are self-contained, ambulatory, noninvasive, unattended ECG recording devices that provide continuous recordings of the electrical activity of the heart for up to 48 hours. Electrodes are placed externally in predetermined locations on an individual’s chest to detect and record the electrical activity of the heart. Individuals maintain a diary of activities and symptoms while wearing the Holter monitor. The information from the Holter ECG, also known as an ambulatory ECG (AECG) device, is reviewed and interpreted by a physician to determine a diagnosis and a treatment plan.

In some cases, longer monitoring periods using diverse types of monitors may be required for intermittent arrhythmias. In this instance, ambulatory event monitors (AEMs), also referred to as loop recorders, may be indicated. AEMs are similar to Holter monitors but allow data collection beyond 48 hours and up to 1 month. With AEMs, the recording device is either continuous, automatically triggered by an arrhythmia, or activated when the individual experiences symptoms. The recorded ECGs are then stored for future analysis and can be transmitted to a receiving station such as a doctor’s office, hospital, or to a cardiac monitoring center attended by technicians 24 hours a day, 7 days a week. Most event recorders can be worn on an individual’s belt or carried in some other manner.

Holter Monitor

AECG using the traditional Holter monitoring devices has been available for many years to diagnose various heart diseases and other conditions that manifest themselves by abnormal cardiac electrical activity (Centers for Medicare & Medicaid Services [CMS], 2004). Holter monitors have a low sensitivity for detecting intermittent arrhythmias. Therefore, they are used to evaluate frequently occurring symptoms (for example, daily or multiple occurrences during the day) and ECG events.

The practice of AECG using a Holter monitor over 24-48 hours has been based on clinical practice guidelines reviewed and published by several specialty societies including the ACC, AHA and the ESC.

Atrial Fibrillation (AF)

Huang (2021) reported the results of a multicenter RCT evaluating whether the detection rate of new AF in individuals with acute ischemic stroke could be improved by performing serial 12-lead ECG compared with conventional 24-hour Holter monitoring. The study involved 826 participants with age ≥ 65 years and no prior history of AF who were randomized to undergo either a 12-lead ECG once daily for 5 days or 24-hour Holter monitoring. The primary outcome was newly detected AF based on intention-to-treat analysis. There was no statistical difference in detection of AF between serial ECGs (8.4%) compared to 24-hour Holter monitoring (6.9%; adjusted odds ratio, 1.17; 95% confidence interval [CI], 0.69 to 2.01). Stepwise multivariate logistic regression revealed that age ≥ 80 years and a history of heart failure were associated with the detection of AF whereas individuals with lacunar infarction had lower odds of detection. The results indicate that 12-lead ECGs once daily for 5 days and 24-hour Holter monitoring are comparable as a first-line assessment tool for the detection of AF in this population. Further evaluation is necessary to understand the long-term impact of these findings on stroke recurrence, anticoagulant therapy, and other outcomes.

Gladstone (2014) reported results for the 30-Day Cardiac Event Monitor Belt for Recording Atrial Fibrillation after a Cerebral Ischemic Event (EMBRACE) randomized controlled trial. EMBRACE assessed noninvasive AECG monitoring with a 30-day event-triggered loop recorder (intervention group) compared to 24-hour Holter monitoring (control group). A total of 572 individuals without known AF, who had had a cryptogenic ischemic stroke or TIA within the previous 6 months, and who received an initial screening with 24-hour Holter monitoring were randomized to the intervention group (n=286) or the control group (n=285). The investigators were unable to assess outcomes for various reasons in 14 individuals who were excluded from the primary analysis and 10 individuals who were excluded from the secondary analysis. The primary outcome was newly detected AF lasting 30 seconds or longer within 90 days after randomization. Secondary outcomes included episodes of AF lasting 2.5 minutes or longer, and anticoagulation status at 90 days. The authors reported the following results:

Atrial fibrillation lasting 30 seconds or longer was detected in 45 of 280 patients (16.1%) in the intervention group, as compared with 9 of 277 (3.2%) in the control group (absolute difference, 12.9 percentage points; 95% confidence interval [CI], 8.0 to 17.6; p<0.001; number needed to screen, 8). Atrial fibrillation lasting 2.5 minutes or longer was present in 28 of 284 patients (9.9%) in the intervention group, as compared with 7 of 277 (2.5%) in the control group (absolute difference, 7.4 percentage points; 95% CI, 3.4 to 11.3; p<0.001). By 90 days, oral anticoagulant therapy had been prescribed for more patients in the intervention group than in the control group (52 of 280 patients [18.6%] vs. 31 of 279 [11.1%]; absolute difference, 7.5 percentage points; 95% CI, 1.6 to 13.3; p=0.01).

The results of this trial demonstrate that noninvasive AECG monitoring with a 30-day event-triggered loop recorder increases the diagnostic yield after initial non-diagnostic Holter monitoring for individuals with cryptogenic ischemic stroke or TIA.

The ACC/AHA Task Force on Practice Guidelines in collaboration with the HRS issued guidelines for the management of individuals with AF (January, 2014). The guidelines recommend electrocardiographic documentation, including Holter monitor, to establish a diagnosis of AF (Level of Evidence: C), and acknowledge that paroxysmal atrial fibrillation (PAF) increases the risk of thromboembolic ischemic stroke. The collaborating organizations subsequently published a focused update to the guidelines that did not specifically address the use of Holter monitors.

In 2014, the AAN published guidelines on the prevention of stroke in nonvalvular AF (NVAF; Culebras, 2022). The guidelines were reaffirmed in 2022 and included the following Level C recommendation:

Clinicians might obtain cardiac rhythm studies for prolonged periods (for example, for one or more weeks) instead of shorter periods (for example, 24 hours) in patients with cryptogenic stroke without known NVAF, to increase the yield of identification of patients with occult NVAF.

The 2017 HRS/EHRA/ECAS/Asia Pacific Heart Rhythm Society (APHRS)/Sociedad Latinoamericana de Estimulación Cardíaca y Electrofisiología (SOLAECE) expert consensus statement on catheter and surgical ablation of AF recommended the following in relation to Holter monitors (Calkins, 2017):

• Minimum documentation for persistent atrial fibrillation: 24-hour Holter within 90 days of the ablation procedure showing continuous atrial fibrillation.
• Minimum documentation for early persistent atrial fibrillation: 24-hour Holter showing continuous atrial fibrillation within 90 days of the ablation procedure.
• Minimum documentation for long-standing persistent atrial fibrillation: 24-hour Holter within 90 days of the ablation procedure showing continuous atrial fibrillation.
• Documentation of atrial fibrillation-related symptoms: Documentation by a physician evaluating the patient that the patient experiences symptoms that could be attributable to atrial fibrillation. This does not require a time-stamped ECG, Holter, or event monitor at the precise time of symptoms. For patients with persistent atrial fibrillation who initially report no symptoms, it is reasonable to reassess symptom status after restoration of sinus rhythm with cardioversion.
• Minimum follow-up screening for paroxysmal atrial fibrillation recurrence: For paroxysmal atrial fibrillation, the minimum follow up screening should include (1) 12-lead ECG at each follow-up visit; (2) 24-hour Holter at the end of the follow-up period (for example, 12 months); and (3) event recording with an event monitor regularly and when symptoms occur from the end of the 3-month blanking period to the end of follow-up (for example, 12 months).
• Minimum follow-up screening for persistent or longstanding atrial fibrillation recurrence: 24-hour Holter every 6 months.

In 2021, the ESC released guidelines for the management of AF, which were developed in collaboration with the European Association for Cardio-Thoracic Surgery (EACTS) (Hindricks, 2021). The guideline included the following statement regarding screening for AF:

When AF is detected by a screening tool, including mobile or wearable devices, a single-lead ECG tracing of ≥ 30 s or 12-lead ECG showing AF analyzed by a physician with expertise in ECG rhythm interpretation is necessary to establish a definitive diagnosis of AF (devices capable of ECG recording enable direct analysis of the device-provided tracings). When AF detection is not based on an ECG recording (for example, with devices using photoplethysmography) or in case of uncertainty in the interpretation of device-provided ECG tracing, a confirmatory ECG diagnosis has to be obtained using additional ECG recording (for example, 12-lead ECG, Holter monitoring, etc.).

The 2021 ESC guideline also included the following recommendations in relation to the search for AF in individuals with cryptogenic stroke:

• In patients with acute ischemic stroke or [transient ischemic attack] (TIA) and without previously known AF, monitoring for AF is recommended using a short-term ECG recording for at least the first 24 hours, followed by continuous ECG monitoring for at least 72 hours whenever possible. (Class I Recommendation; Level of Evidence B)
• In selected stroke patients without previously known AF, additional ECG monitoring using long-term non-invasive ECG monitors or insertable cardiac monitors should be considered, to detect AF. (Class IIa Recommendation; Level of Evidence B)

In 2022, the Untied Stated Preventive Services Task Force (USPSTF) published an evidence summary concluding that screening can detect more cases of unknown AF but the evidence regarding the effects of screening on health outcomes is limited.

In 2023, the ACC in conjunction with the AHA, American College of Chest Physicians (ACCP) and the HRS published Guidelines for the Diagnosis and Management of Atrial Fibrillation. The recommendation includes the following:

In patients with stroke or TIA of undetermined cause, initial cardiac monitoring and, if needed, extended monitoring with an implantable loop recorder (ILR) are reasonable to improve detection of AF.

The Committee cited relevant studies that analyzed AF in individuals with recent stroke, including the following:

• The EMBRACE (30 Day Event Monitoring Belt for Recording Atrial Fibrillation After a Cerebral Ischemic Event) trial, which randomized 572 individuals aged 55 or older with recent cryptogenic stroke or TIA to either 30-day external loop recorder (ELR) or conventional 24-hour Holter monitoring, extended monitoring was associated with higher rates of AF detection at 90 days.
• The CRYSTAL-AF (Cryptogenic Stroke and Underlying AF) trial randomized 441 individuals aged 40 years or older with recent cryptogenic stroke or TIA to cardiac monitoring with either insertable loop recorder or conventional follow-up ECGs. Implantable recorder was superior in detecting AF at 6 months (8.9% compared to 1.4%), 12 months (12.4% compared to 2.0%), and 3 years (30% compared to 3%).
• The FIND-AF (Future Innovations in Novel Detection of Atrial Fibrillation), which compared repeated sets of 10-day Holter monitoring (at baseline, 3-months, and 6-months) to conventional 24-Holter in individuals aged 60 years or older with recent stroke, higher rates of detection were associated with repeated monitoring (14% compared to 5%; absolute difference, 9.0% [95% CI, 3.4-14.5]; p=0.002).
• The PER DIEM (Post-Embolic Rhythm Detection with Implantable versus External Monitoring) RCT also showed a larger proportion of patients with AF detected at 1 year with prolonged monitoring.

The committee concluded that additional studies are needed to determine whether extended cardiac monitoring improves long-term clinical outcomes after stroke.

Noting a wide range of available medical and consumer heart rhythm monitoring devices, the ACC established a standardized approach for interpreting and managing monitoring data to guide clinical utilization. The ACC published this guidance in the Expert Consensus Decision Pathway on Practical Approaches for Arrhythmia Monitoring After Stroke (Spooner, ACC, 2025). Relevant recommendations include the following:

1. In patients with stroke from presumed cardioembolic origin, the role for rhythm monitoring is limited, given an indication that necessitates persistent anticoagulation. Monitoring should only be considered if there is consideration of stopping anticoagulation or there are other treatment decisions that depend on arrhythmia detection.
2. In patients with ischemic stroke from presumed small- or large-vessel disease, it is reasonable to monitor patients for 2-4 weeks, with the addition of oral anticoagulation should an AF event ≥ 5 minutes be identified.
4. In patients with embolic stroke of undetermined source, cardiac monitoring (2-4 weeks) should be offered to patients if they are a candidate for long-term anticoagulation should AF be identified.
6. It is reasonable to consider anticoagulation in patients with AF events ≥ 5 minutes, particularly in those with a CHA₂DS₂-VASc score greater than or equal to 3 or equivalent stroke risk.

The ACC states that, while enhanced cardiac monitoring improves the detection of arrhythmias following a stroke, the impact of this increased detection on preventing recurrent strokes remains uncertain. Importantly, the Expert Consensus Decision Pathway is limited in scope to individuals with ischemic or embolic stroke. Although the document defines transient ischemic attack (TIA) for contextual purposes, it does not issue recommendations regarding arrhythmia monitoring after TIA, nor does it describe monitoring strategies, thresholds for anticoagulation, or durations of external or implantable monitoring for individuals with TIA. As a result, the ACC pathway should not be interpreted as applying to TIA.

The ARCADIA trial, as analyzed by Kamel (2025), investigated whether apixaban offers benefit over antiplatelet therapy for secondary stroke prevention in individuals with a recent cryptogenic stroke and biomarker evidence of atrial cardiopathy but without known atrial fibrillation. In the primary analysis, apixaban did not reduce the risk of recurrent stroke compared with aspirin, providing no support for anticoagulation in this population in the absence of documented atrial fibrillation. Participants in the secondary analysis published in 2025 were monitored for AF using two main methods: EAMs and ILRs. Out of 1633 participants, 58.6% underwent prolonged heart rhythm monitoring, with 34.7% using EAMs, 29.3% using ILRs, and 5.5% using both. The analysis highlighted several factors as strong predictors of undergoing monitoring, including Hispanic ethnicity, National Institutes of Health (NIH) Stroke Scale score, left atrial diameter, and serum hemoglobin levels. The use of ILRs was significantly associated with a higher likelihood of detecting AF, with a relative risk of 3.9 (95% CI, 2.1-7.4), but did not modify the trial treatment effect (p=0.99). These findings suggest that atrial cardiopathy alone, as defined by the trial’s biomarker criteria (for example: NT-proBNP levels, P-wave terminal force in V1, left atrial diameter index), does not identify a subgroup that experiences improved outcomes with routine anticoagulation, and reinforce the approach of reserving anticoagulation for people in whom atrial fibrillation is actually detected.

Murphy (2025) conducted a randomized cross-over trial assessing the effectiveness of one-week of ELR monitoring for AF detection in adults aged ≥ 55 years with a CHA₂DS₂-VASc score > 2. Among 488 participants, immediate ELR monitoring identified AF in 6.6% compared to 1% with usual care (absolute difference 5.5%, p<0.001). Over one-third (37.5%) of ELR-detected AF episodes lasted >24 hours, and all detected cases led to initiation of oral anticoagulation. The study demonstrated that short-term ELR monitoring significantly increases new AF detection compared with standard pulse and ECG screening in high-risk adults. The usual care arm of the trial relied on a 2-minute pulse monitoring for AF detection, likely representing a minimal comparator. The authors acknowledge that the trial was not powered to assess clinical outcomes such as stroke or bleeding. As a result, the findings inform detection rates only, and do not establish whether increased identification of AF leads to improvements in outcomes that matter to individuals, such as stroke prevention or avoidance of harm.

Other Cardiac Arrhythmias and Syncope

Across several older studies, ambulatory electrocardiographic (AECG) monitoring was evaluated for arrhythmia detection, risk stratification, and autonomic assessment, with generally limited implications for current policy. In a systematic review of diagnostic tools for individuals presenting with palpitations (Hoefman, 2010), auto-triggered event recorders demonstrated the highest diagnostic yield, followed by participant-activated devices and Holter monitors; however, substantial heterogeneity prevented firm recommendations, supporting coverage guidelines that allow flexible selection of monitoring technologies based on symptom characteristics rather than mandating a specific device.

In guideline recommendations for hypertrophic cardiomyopathy (Gersh, 2011), 24-hour Holter monitoring was advised during initial evaluation and when individuals experience palpitations or lightheadedness, findings that align with current targeted indications and do not support broader routine use.

In an additional application of Holter-derived metrics (Calkins, 2017), simple autonomic function tests, particularly the Valsalva ratio, 30:15 ratio, and handgrip test, were significant predictors of cardiovascular autonomic neuropathy and all-cause mortality among individuals with diabetes, suggesting no policy need to rely on 24-hour Holter monitoring for this purpose. Collectively, these studies support maintaining existing, symptom- or condition-specific use criteria for AECG monitoring.

The EHRA/HRS/APHRS 2014 expert consensus document on ventricular arrhythmias (VAs) included the following recommendation for the general diagnostic work-up of non-sustained VAs:

Prolonged ECG monitoring by Holter ECG, prolonged ECG event monitoring, or ILRs should be considered when documentation of further, potentially longer arrhythmias would change management (class IIa, level of evidence C).

The International Society for Holter and Noninvasive Electrocardiology (ISHNE) and the HRS 2017 expert consensus statement on AECG and external cardiac monitoring/telemetry included recommendations on a variety of devices used to detect cardiac arrhythmias and/or arrhythmia patterns which cannot be easily diagnosed through standard ECG. The guidelines note:

AECG telemetry is typically used to evaluate symptoms such as syncope, dizziness, chest pain, palpitations, or shortness of breath, which may correlate with intermittent cardiac arrhythmias. Additionally, AECG is used to evaluate patient response to initiation, revision, or discontinuation of arrhythmic drug therapy and to assess prognosis in specific clinical contexts.

The 2017 ACC/AHA/HRS guideline on the management of syncope noted that several external cardiac monitoring approaches, including Holter monitors, may be used to evaluate syncope in a select group of ambulatory individuals with syncope of suspected arrhythmic etiology (IIa recommendation) (Shen, 2017). The guideline also noted that other devices with longer monitoring periods may confer a higher yield than Holter monitoring and may be useful after a negative Holter evaluation.

In the 2017 ACC/AHA/HRS guideline on the management of VA and the prevention of sudden cardiac death (Al-Khatib, 2017), continuous 24-hour Holter recording was deemed, “appropriate when symptoms occur at least once a day or when quantitation of PVCs/NSVT is desired to assess possible VA-related depressed ventricular function.” Conventional standard external and implantable AEMs were considered more appropriate for sporadic episodes of palpitations, dizziness or syncope.

The AAP released an updated position statement titled Sudden Death in the Young: Information for the Primary Care Provider addressing the risk of sudden cardiac arrest (SCA) or sudden cardiac death (SCD) in children (Erickson, 2021). The previous AAP guidelines from 2012 focused on screening children, particularly before athletic participation. The 2021 update expands the scope of recommendations to include broader prevention strategies. AAP recommends the following:

First-degree family members of patients with SCA and SCD be informed of the potentially increased risk. An assessment should be offered at a center with experience in the diagnosis and management of inherited cardiac diseases. The initial battery of tests for first-degree relatives usually includes a visit to a pediatric cardiologist or electrophysiologist, an ECG, an exercise stress test (if old enough to exercise), and an echocardiogram. It is reasonable to order molecular genetic testing from the victim after SCA. If a disease-causing variant is identified in the victim, cascade molecular and clinical screening of family members is indicated. Cascade screening means evaluation beginning with first-degree relatives of the SCA victim. Depending on the results of those screening tests, other family members may need testing as well.

In this document, AAP does not recommend use of external AEMs in the initial evaluation of individuals with a family history of SCA or SCD; however, the investigations described above may reveal a condition for which AEM use may be considered medically necessary.

Another ACC/AHA/HRS guideline on the evaluation and management of individuals with bradycardia and cardiac conduction delay (Kusumoto, 2019) recommended the following:

In the evaluation of patients with documented or suspected bradycardia or conduction disorders, cardiac rhythm monitoring is useful to establish correlation between heart rate or conduction abnormalities with symptoms, with the specific type of cardiac monitor chosen based on the frequency and nature of symptoms, as well as patient preferences (Strength of Recommendation: Strong; Level of Evidence: Moderate-quality with nonrandomized studies).

There are several cardiovascular monitoring devices (Holter monitors) that have received U.S. Food & Drug Administration 510(k) clearances as Class II devices. Some newer devices are continuous monitors that are similar to traditional AECG Holter monitoring in concept, but offer other features such as the ability to monitor for longer periods of time.

External Ambulatory Event Monitor

In 1999, the ACC, in conjunction with other organizations, published clinical guidelines for ambulatory electrocardiography. This guideline has not been updated but remains active. It made the following Class I recommendations (Crawford, 1999):

• Individuals with unexplained syncope, near syncope, or episodic dizziness in whom the cause is not obvious;
• Individuals with unexplained recurrent palpitation;
• To assess antiarrhythmic drug response in individuals in whom baseline frequency of arrhythmia has been characterized as reproducible and of sufficient frequency to permit analysis.

There were two Class IIa recommendations as follows:

• To detect proarrhythmic responses to antiarrhythmic therapy in individuals at high- risk;
• Individuals with suspected variant angina.

These guidelines describe both Holter monitor and AEM devices but the recommendations do not distinguish between the types of monitors. These guidelines also predate the commercial availability of ELRs with auto-triggered capability or ILR. However, these guidelines are helpful to define the indications for ambulatory ECG in general, with the choice of a specific device based on the frequency of symptoms.

Of the Class I and IIa recommendations listed above, only the assessment of unexplained symptoms, such as syncope and palpitation, would occur infrequently enough to warrant the use of an AEM. The other indications could be adequately assessed with short-term monitoring with a Holter monitor. Additionally, in 2001, the ACC published a clinical competence statement on ECG and ambulatory ECG, which reiterated the indications for ambulatory ECG addressed in the 1999 clinical guidelines (Kadish, 2001). The competence statement noted:

There are no specific guidelines that distinguish patients for whom it is appropriate to perform continuous monitoring, (i.e., Holter monitor) from those for whom intermittent ambulatory monitoring is adequate. However, when monitoring is performed to evaluate the cause of intermittent symptoms, the frequency of the symptoms should dictate the type of recording.

In 2017, the AHA, in conjunction with the ACC, and the HRS, published a guideline on the evaluation and management of syncope. The guideline for cardiac monitoring includes the following Class I recommendation:

• The choice of a specific cardiac monitor should be determined on the basis of the frequency and nature of syncope events.

The second recommendation for ambulatory individuals is a Class IIa recommendation:

• To evaluate selected ambulatory patients with syncope of suspected arrhythmic etiology, the following external cardiac monitoring approaches can be useful:
  1. Holter monitor
  2. Trans-telephonic monitor
  3. ELR
  4. Patch recorder
  5. Mobile cardiac outpatient telemetry

In 2017, the AHA/ACC/HRS published a guideline for the management of individuals with VA and prevention of sudden cardiac death. The guideline does not recommend ambulatory monitoring when suspicion of VA is high as diagnosis needs to be made quickly to prevent VA. Ambulatory monitoring is recommended in the following Class I recommendation:

• Ambulatory electrocardiographic monitoring is useful to evaluate whether symptoms, including palpitations, presyncope, or syncope, are caused by VA.

In 2020, the AHA/ACC published a guideline for the diagnosis and treatment of HCM which includes recommendations for heart rhythm assessment. The following Class 1 recommendation for AEMs are:

• In patients with HCM who develop palpitations or lightheadedness, extended (> 24 hours) electrocardiographic monitoring or event recording is recommended, which should not be considered diagnostic unless patients have had symptoms while being monitored.

The Class 2a and 2b (respectively) recommendations include:

• In patients with HCM who have additional risk factors for atrial fibrillation (AF), such as left atrial dilatation, advanced age, and New York Heart Association (NYHA) class III to class IV heart failure (HF), and who are eligible for anticoagulation, extended ambulatory monitoring is reasonable to screen for AF as part of initial evaluation and periodic follow-up (every 1 to 2 years).
• In adult patients with HCM without risk factors for AF and who are eligible for anticoagulation, extended ambulatory monitoring may be considered to assess for asymptomatic paroxysmal AF as part of initial evaluation and periodic follow-up (every 1 to 2 years).

Monitoring for AF in the post-cryptogenic stroke setting:

The term cryptogenic stroke describes a cerebral infarction without an identifiable cause, specifically a cardioembolic source, such as a patent foramen ovale or AF. When potential cardiovascular etiologies have been ruled out during an initial workup consisting of various imaging studies and ECGs, it is considered a “cryptogenic” stroke. It is estimated that some 36% of stroke survivors have cryptogenic stroke. Additional monitoring may identify AF in stroke initially categorized as cryptogenic (Tayal, 2008). The presence or absence of AF has a significant impact on post-stroke management.

In 2007, Liao conducted a systematic review of noninvasive cardiac monitoring in the post-stroke setting where the authors specifically sought to determine the frequency of occult AF detected by noninvasive methods of continuous cardiac rhythm monitoring in consecutive individuals with ischemic stroke; a total of five prospective case series were included in the analysis. The two studies that focused on loop recorders, following a negative HM finding, are relevant to this discussion (Barthelemy, 2003; Jaboudon, 2004). New AF was identified in 5.7% and 7.7% of participants, respectively. In the study by Jaboudon, oral anticoagulation was started in 2 of the 7 participants with new onset AF. The authors concluded that increased duration of monitoring appears to be associated with increased rates of detection of AF; however, the authors also comment that it is uncertain whether any type of monitoring, including HM, should be routinely performed given the low incidence of AF.

Buck and colleagues (2021) published the results of an open-label RCT evaluating the detection of occurrences of AF in individuals with a recent stroke by means of ILR monitoring for 12 months compared with conventional  ELR monitoring for 30 days. The study involved 300 participants within 6 months of ischemic stroke and without known AF across three centers. Participants were randomized 1:1 to receive either an ILR (Reveal LINQ; Medtronic, Inc., Minneapolis, MN) plus remote monitoring for 12 months or monitoring with an ELR (SpiderFlash-t; Sorin Group Italia S.R.L, Burnaby, British Columbia) for 30 days with follow-up visits at 30 days, 6 months, and 12 months. The primary outcome was the development of definite AF or highly probable AF (adjudicated new AF lasting ≥ 2 minutes within 12 months of randomization). At baseline, it was determined that 66.3% of participants had an index stroke of undetermined etiology using the Trial of ORG in Acute Stroke Treatment (TOAST) classification. Of the 300 randomized participants, a total of 273 (91%) completed cardiac monitoring lasting 24 hours or longer and 259 (86.3%) completed both the assigned monitoring and 12-month follow-up visit. The primary outcome of development of definite or highly probable AF within 12 months was observed in 15.3% (23/150) of participants in the ILR group and 4.7% (7/150) of participants in the  ELR group (between-group difference, 10.7% [95% CI, 4% to 17.3%]; risk ratio, 3.29 [95% CI, 1.45 to 7.42]; p=0.003). This indicates that approximately 1 additional person was diagnosed with AF for every 10 persons monitored with an ILR . In the first 30 days from randomization there were 7 (4.7%) new AF diagnoses in the ILR group and 5 (3.3%) in the ELR group (between-group difference, 1.3% [95% CI, -3.1% to 5.8%]; p=0.77). Between 30 days and 12 months there were significantly (p=0.001) more cases of AF diagnosed in the ILR group (n=16) compared with the ELR group (n=2). All AF diagnoses resulted in new prescriptions for anticoagulant therapy. The only significant features associated with AF detection were older age (p=0.002) and device group (p=0.004). There were no significant between group differences for secondary outcomes of TIA, recurrent ischemic attack, intracerebral hemorrhage, or death. In this study, although the use of an ILR over the period of 12 months led to the higher detection of AF compared to monitoring with an ELR over 30 days, it remains unclear whether this results in a lower incidence of strokes or other patient-centered outcomes.

The CRYSTAL-AF trial (Sanna, 2014) was a large, multicenter, prospective, manufacturer-sponsored randomized controlled study that assigned 441 individuals with recent cryptogenic stroke or TIA and no prior AF to either usual care (n=220) or continuous long-term rhythm surveillance with an ICM (n=221) to determine whether extended monitoring improved AF detection. The trial demonstrated substantially higher AF detection in the ICM group at 6 months (8.9% vs. 1.4%), 12 months (12.4% vs. 2.0%), and up to 36 months (30.0% vs. 3.0%), with most detected episodes being asymptomatic and paroxysmal. Strengths of the study include its randomized design, adjudicated endpoints, long follow-up, and consistent subgroup effects. Limitations include its modest sample size for long-term follow-up and the absence of evidence that increased AF detection translated into reductions in recurrent stroke.

Similar results were noted from another open-label, multi-center, randomized controlled trial, the 30-Day Cardiac Event Monitor Belt for Recording Atrial Fibrillation after a Cerebral Ischemic Event (EMBRACE) trial that enrolled 572 participants with cryptogenic stroke or TIA of undetermined cause within the previous 6 months and no history of AF (Gladstone, 2014). Trial participants were randomized to receive noninvasive ambulatory ECG monitoring with either a 30-day event-triggered loop recorder (intervention group) or a conventional 24-hour HM (control group). The primary outcome was newly detected AF lasting 30 seconds or longer within 90 days after randomization. Secondary outcomes included episodes of AF lasting 2.5 minutes or longer and anticoagulation status at 90 days. At 30 days, results indicated that AF lasting 30 seconds or longer was detected in 45 of 280 participants (16.1%) in the intervention group, as compared with 9 of 277 (3.2%) in the control group (absolute difference, 12.9 percentage points; 95% CI, 8.0 to 17.6; p<0.001; number needed to screen, 8). Episodes of AF lasting 2.5 minutes or longer were present in 28 of 284 participants (9.9%) in the intervention group, as compared with 7 of 277 (2.5%) in the control group (absolute difference, 7.4 percentage points; 95% CI, 3.4 to 11.3; p<0.001). By 90 days, oral anticoagulant therapy had been prescribed for more individuals in the intervention group than in the control group (52 of 280 [18.6%] vs. 31 of 279 [11.1%]; absolute difference, 7.5 percentage points; 95% CI, 1.6 to 13.3; p=0.01). This trial’s results demonstrated that noninvasive ambulatory ECG monitoring for 30 days is superior to short-term 24 hour monitoring for the detection of AF in individuals with a history of stroke or TIA labeled as cryptogenic but the trial did not demonstrate therapeutic benefit from anticoagulation therapy in this population.

Additional published evidence includes a systematic review and meta-analysis conducted by Kishore in 2014 to determine the frequency of newly detected AF using noninvasive or invasive cardiac monitoring after ischemic stroke or TIA. Prospective observational studies or randomized controlled trials of individuals with ischemic stroke, TIA, or both, who underwent any cardiac monitoring for a minimum of 12 hours, were included after electronic searches of multiple databases. The primary outcome was detection of any new AF during the monitoring period. A total of 32 studies were analyzed. The overall detection rate of any AF was 11.5% (95% CI, 8.9%-4.3%), although the timing, duration, method of monitoring, and reporting of diagnostic criteria used for paroxysmal AF varied. Results showed that detection rates were higher in selected participants (13.4%; 95% CI, 9.0%-18.4%), as compared to unselected participants (6.2%; 95% CI, 4.4%-8.3%). The authors noted the presence of substantial heterogeneity even within specified subgroups and concluded that detection of AF was highly variable. This review was limited by small sample sizes and marked heterogeneity.

In 2019, the AHA/ACC/HRS update the guidelines for AF and includes a Class IIa recommendation for device detection of AF and atrial flutter (January 2019):

• In patients with cryptogenic stroke (for example, stroke of unknown cause) in whom external ambulatory monitoring is inconclusive, implantation of a cardiac monitor (loop recorder) is reasonable to optimize detection of silent AF.

In 2021, the AHA and American Stroke Association (ASA) (Kleindorfer, 2021) updated the guidelines for the prevention of stroke in individuals with a history of stroke and TIA. The guidelines include a Class IIa recommendation for the use of long-term rhythm monitoring to detect intermittent AF:

• In patients with cryptogenic stroke who do not have a contraindication to anticoagulation, long-term rhythm monitoring with mobile cardiac outpatient telemetry, implantable loop recorder, or other approach is reasonable to detect intermittent AF.

In 2022, the Guideline Development Subcommittee of the AAN issued updated guidelines on the prevention of stroke in patients with NVAF. This update to the former 1998 AAN practice parameter on stroke prevention in NVAF focuses on medical strategies to reduce risk of ischemic stroke but also provided the following regarding identification of individuals with occult NVAF:

• Clinicians might obtain outpatient cardiac rhythm studies in patients with cryptogenic stroke without known NVAF to identify patients with occult NVAF (Level C***);
• Clinicians might obtain cardiac rhythm studies for prolonged periods (for example, for 1 or more weeks) instead of shorter periods (for example, 24 hours) in patients with cryptogenic stroke without known NVAF, to increase the yield of identification of patients with occult NVAF (Level of evidence: C***);
• Clinicians should routinely offer anticoagulation to patients with NVAF and a history of TIA or stroke to reduce these patients’ subsequent risk of ischemic stroke ( (Level B**);
• To inform their judgments as to which patients with NVAF might benefit more from anticoagulation, clinicians should use a risk stratification scheme to help identify patients with NVAF who are at higher risk for stroke or at no clinically significant risk. However, clinicians should not rigidly interpret anticoagulation thresholds suggested by these tools as being definitive indicators of which patients require anticoagulation (Level B**);
• Specific patient considerations will inform anticoagulant selection in patients with NVAF judged to need anticoagulation (Culebras, 2022).             

Levels of Evidence are provided as follows for the AAN guideline recommendations above:
**B:   Data derived from a single randomized trial or nonrandomized studies;
***C:  Low confidence in evidence, small benefit relative to harm (AAN, 2014).

Monitoring for AF in the post-ablation setting:

Ablation is an option for treatment of AF in individuals with symptomatic AF who are refractory or intolerant to pharmacologic management and in selected individuals with heart failure (HF) or reduced left ventricular ejection fraction (LVEF).

The ACC/AHA/ESC Guidelines on the Management of AF address the role of ablation techniques, and note:

The long term efficacy of catheter ablation to prevent recurrent AF requires further study. Available data demonstrate 1 year or more free from recurrent AF in most (albeit, carefully selected) patients. It is important to bear in mind, however, that AF can recur without symptoms and be unrecognized by the patient or the physician. Therefore, it remains uncertain whether apparent cures represent elimination of AF or transformation into an asymptomatic form of paroxysmal AF. The distinction has important implications for the duration of anticoagulation treatment (Fuster, 2006).

A 2011, the ACCF/AHA/HRS focused update to the ACC/AHA/ESC Guidelines on the Management of AF includes HM and longer term event recording in its recommendations for initial clinical evaluation if the diagnosis or type of arrhythmia is in question and also in subsequent treatment monitoring as a means of evaluating rate control and individual risk for thromboembolic events (Fuster, 2011). This document reviews the major clinical trials of various treatment strategies for AF and notes, “The optimum method for monitoring antiarrhythmic drug treatment varies with the agent involved, as well as with patient factors.” The following is excerpted:

Ambulatory ECG recordings and device-based monitoring have revealed that an individual may experience periods of both symptomatic and asymptomatic AF…Prolonged or frequent monitoring may be necessary to reveal episodes of asymptomatic AF, which may be a cause of cryptogenic stroke.

In 2014, the AHA/ACC/HRS updated its Guidelines on the Management of Patients with Atrial Fibrillation which referred to ILR, pacemakers and defibrillators as, “Offer the possibility to report the frequency, rate, and duration of abnormal atrial rhythms including AF” (January, 2014). No additional information or recommendations for use of ILRs were provided in this document.

Based on available published evidence, there is inadequate data to support the use of AEMs in post-ablation therapy to determine the need for continued anticoagulation therapy (Chao, 2011).

Monitoring in other study populations:

Ha and colleagues (2021) published the results of an open-label, multicenter, RCT aimed at determining whether continuous cardiac rhythm monitoring enhances the detection of postoperative AF (POAF) among individuals undergoing cardiac surgery during the first 30 days following hospital discharge compared with usual care. The study involved individuals with CHA₂DS₂-VASc (a point-based tool used to stratify risk of stroke in individuals with AF) scores greater ≥ 4 or ≥ 2 with at least 1 additional risk factor for POAF, no history of preoperative AF, and POAF lasting less than 24 hours during hospitalization. The intervention group underwent continuous cardiac rhythm monitoring with a wearable, patch-based monitor for 30 days after randomization. Monitoring was not mandated in the usual care group. The primary outcome was cumulative AF and/or atrial flutter lasting 6 minutes or longer detected by continuous cardiac rhythm monitoring or 12-lead ECG within 30 days of randomization. A total of 336 individuals were randomized (163 individuals in the intervention group and 173 individuals in the usual care group), though 307 (91.4%) completed the trial. In the intent-to-treat analysis, the primary endpoint occurred in 32 participants (19.6%) in the intervention group compared to 3 participants (1.7%) in the usual care group (absolute difference, 17.9%; 95% CI, 11.5% to 24.3%; p<0.001). The majority of cumulative AF or atrial flutter in the intervention group occurred within the first 2 weeks of monitoring (n=35) compared to the last 2 weeks (n=6). In this study population, continuous monitoring detected significantly more POAF after discharge compared to usual care. However, the study was not designed to assess differences in major adverse cardiovascular outcomes, stroke rates in the presence of POAF, or the effects of anticoagulant therapy for this population.

The CARISMA study (Cardiac Arrhythmias and Risk Stratification After MyoCardial Infarction) investigated the incidence and prognostic significance of arrhythmias, documented by use of an ILR, in individuals following acute myocardial infarction (MI) with left ventricular systolic dysfunction. After exclusions, 297 participants (21%) (mean ± SD age 64.0 ± 11.0 years; LVEF 31 ± 7%) received an ILR within 11 ± 5 days of the acute MI and were followed every 3 months for an average of 1.9 ± 0.5 years. Predefined bradyarrhythmias and tachyarrhythmias were recorded in 137 participants (46%); 86% of these were asymptomatic. The ILR documented a 28% incidence of new-onset AF with fast ventricular response (≥ 125 bpm), a 13% incidence of nonsustained ventricular tachycardia (≥ 16 beats), a 10% incidence of high-degree atrioventricular block (≤ 30 bpm lasting ≥ 8 seconds), a 7% incidence of sinus bradycardia (≤ 30 bpm lasting ≥ 8 seconds), a 5% incidence of sinus arrest (≥ 5 seconds), a 3% incidence of sustained ventricular tachycardia, and a 3% incidence of ventricular fibrillation. Cox regression analysis with time-dependent covariates revealed that high-degree atrioventricular block was the most powerful predictor of cardiac death (hazard ratio [HR], 6.75; 95% CI, 2.55 to 17.84; p<0.001). In this first study to report on long-term cardiac arrhythmias, recorded by an ILR in individuals with an LVEF ≤ 40% after MI, the authors concluded that clinically significant bradyarrhythmias and tachyarrhythmias were documented in a substantial proportion of study participants with depressed LVEF after acute MI and that intermittent high-degree atrioventricular block was associated with a very high risk of cardiac death (Bloch, 2010).

A substudy of the CARISMA investigated the incidence and risk associated with new-onset AF occurring after discharge in participants following an acute MI (Jons, 2011). This study included 271 post-MI participants with an LVEF ≤ 40% and no history of previous AF. All trial participants were implanted with an ILR and followed up every 3 months for 2 years. Major cardiovascular events were defined as reinfarction, stroke, hospitalization for HF, or death. Results showed the risk of new-onset AF is highest during the first 2 months after the acute MI (16% event rate) and decreases until month 12 post-MI, after which the risk for new-onset AF is stable. The risk of major cardiovascular events was increased in participants with AF events lasting ≥ 30 seconds (HR [95% CI], 2.73 [1.35 to 5.50], p=0.005), but not in participants with AF events lasting < 30 seconds (HR [95% CI], 1.17 [0.35 to 3.92], p=0.80). More than 90% of all recorded AF events were asymptomatic. The authors concluded that, through use of an ILR, the incidence of new-onset AF was found to be 4-fold higher than earlier reported. In the study population in which treatment with beta-blockers was optimized, the vast majority of AF events were asymptomatic, and a duration of 30 seconds or more identified clinically important AF episodes.

Up to 30% of individuals who undergo coronary artery bypass grafting (CABG) experience new-onset AF in the postoperative period. A prospective cohort study of 198 participants undergoing isolated CABG with preserved ejection fraction and no prior arrhythmias used intraoperative insertion of an implantable cardiac monitor to provide continuous rhythm surveillance for 12 months (Herrmann, 2025). This study found that, although the cumulative incidence of new-onset AF approached 48%, AF episodes were overwhelmingly brief, occurred almost entirely within the first 7-30 postoperative days, and resulted in a median annual AF burden of just 0.07%, with virtually no sustained episodes after day 30. No strokes occurred in participants with new-onset AF during follow-up, and episodes lasting ≥24 hours were rare and predominantly confined to the index hospitalization. These findings suggest that while AF after CABG is more common than previously appreciated, its burden beyond 30 days is extremely low, supporting a recommendation that if oral anticoagulation is initiated for new-onset postoperative AF, the need for continuation should be reassessed at 30 days based on rhythm profile and patient-specific thromboembolic risk. This study did not assess the value of anticoagulation for individuals experiencing AF after CABG.

Additional considerations:

Devices are becoming available with enhanced recording capability, such as the Zio^®Patch (iRhythm Technologies, Inc., San Francisco, CA) which obtained FDA clearance in 2012 for, “Prescription only single patient use, continuous recording EGG monitor that can be worn for up to 14 days. It is indicated for use on patients who experience transient symptoms, such as syncope, palpitations, shortness of breath, or chest pains” (FDA, 2012). To date, the published evidence regarding these newer devices is limited regarding safety/efficacy and impact on clinical outcomes.

*The CHADS2 (cardiac failure, hypertension, age, diabetes, stroke) score is a risk assessment tool that is based on a point system, in which 2 points are assigned for a history of stroke or TIA, and 1 point each is assigned for age over 75 and a history of hypertension, diabetes or recent HF. The adjusted stroke rate can be assessed based on the CHADS2 score. For example, a CHADS2 score of 2 is associated with an adjusted stroke rate of 4% per year (Fuster, 2006).

Arrhythmia: Abnormal heart rhythms which may be classified as either atrial or ventricular, depending on the origin in the heart. Individuals with arrhythmias may experience a wide variety of symptoms ranging from palpitations to fainting.

Atrial fibrillation: A quivering or irregular heartbeat (arrhythmia) that can lead to blood clots, stroke, heart failure and other heart-related complications.

CHADS₂ score: a 5-factor, point-based clinical tool developed to estimate stroke risk in individuals with nonvalvular atrial fibrillation. While historically important and easy to use, it underestimates risk in many individuals because it omits several validated stroke predictors. The CHA₂DS₂-VASc score supplanted CHADS₂ because it improves identification of truly low-risk individuals, provides better discrimination among intermediate-risk patients, incorporates additional validated risk factors, and is endorsed by contemporary U.S. cardiology guidelines. As a result, CHA₂DS₂-VASc is now the standard tool for stroke risk stratification and anticoagulation decision-making in atrial fibrillation.

CHA₂DS₂-VASc Score: A validated clinical risk stratification tool used to estimate the likelihood of stroke in individuals with atrial fibrillation (Lip, 2011). The acronym reflects the weighted components of the score:

*Note: The gender descriptions used in this document, ‘biological male and ‘biological female’ refer to sex assignment at birth and are used to clarify the cardiovascular risk of the individual, regardless of gender identity or expression.

CHA₂DS₂-VASc scores range from 0 to 9 and are used to estimate relative thromboembolic risk and inform decisions regarding antithrombotic therapy in individuals with atrial fibrillation. Current guidelines divide individuals at risk for ischemic stroke with a CHA2DS2-VASc scores into 3 categories:

• low-risk = 0
• intermediate = 1-2
• high risk ≥ 3

A CHA₂DS₂-VASc score of 1 based on female sex alone is not considered sufficient to warrant anticoagulation. Anticoagulation recommendations typically begin at a CHA₂DS₂-VASc score ≥ 2 for men and ≥ 3 for women (Joglar, 2023).

Cryptogenic stroke: Cerebral infarction that despite evaluation is not attributable to other well-established singular etiologies including cardioembolism, large artery atherosclerosis, thromboembolism, or small vessel occlusion.

Left atrial diameter index: An echocardiographic measure of left atrial size adjusted for body surface area. Enlargement of the left atrial diameter index may reflect structural atrial remodeling and is one of the echocardiographic biomarkers used in defining atrial cardiopathy in clinical trials assessing risk of stroke and atrial fibrillation.

Myopotential: The electric signal originating from skeletal muscle (usually the pectoralis major), close to a pacemaker, which may be sensed by the pacemaker during activity and falsely interpreted as a depolarization.

NT-proBNP levels: A circulating biomarker released by cardiac myocytes in response to myocardial wall stress. Elevated N-terminal pro-B-type natriuretic peptide (NT-proBNP) levels may indicate structural or functional atrial abnormalities and have been used in clinical research as one component of atrial cardiopathy in studies evaluating stroke mechanisms and atrial fibrillation detection.

Physiological pacing: A dual chamber or atrium-based pacing device used to maintain atrioventricular synchrony.

P-wave terminal force in V1: An electrocardiographic biometric measure reflecting left atrial electrical activity, defined as the product of the depth and duration of the terminal negative portion of the P wave in lead V1. Increased P-wave terminal force in V1 is associated with abnormal atrial conduction and has been used as a marker of atrial cardiopathy in stroke-related research.

Rate-responsive pacing: A pacemaker that can vary the pacing rate, depending on the immediate needs of the individual using sensors of body motion or respiratory rate.

Stroke: A neurological deficit attributed to an acute focal injury of the central nervous system caused by a vascular event. Stroke includes infarction of the brain, spinal cord, or retina as demonstrated by neuropathological, neuroimaging, or clinical evidence of permanent injury. The 2 major types of stroke are embolic and ischemic stroke:

Embolic stroke: A cerebral infarction caused by an embolus originating outside the intracranial circulation, most commonly from the heart, that travels through the bloodstream and acutely occludes a cerebral artery, leading to interruption of cerebral blood flow and resulting neurological deficits.

Ischemic Stroke: A cerebral infarction caused by obstruction of blood flow to brain tissue, most commonly due to thrombosis or embolism, resulting in acute neurological deficits and loss of viable brain tissue.

Syncope: An episode where the individual experiences loss of consciousness lasting at least several seconds. If extreme dizziness is experienced without actual loss of consciousness, this is termed "pre- syncope."

Tachycardia: An abnormally rapid heartbeat.

Transient ischemic attack (TIA): A transient episode of neurological dysfunction lasting less than 24 hours, caused by focal brain, spinal cord, or retinal ischemia without evidence of acute infarction on imaging.

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30. Tung CE, Su D, Turakhia MP, et al. Diagnostic yield of extended cardiac patch monitoring in patients with stroke or TIA. Front Neurol. 2014; 5:266.
31. Ziegler PD, Glotzer TV, Daoud EG, et al. Detection of previously undiagnosed atrial fibrillation in patients with stroke risk factors and usefulness of continuous monitoring in primary stroke prevention. Am J Cardiol. 2012; 110(9):1309-1314.

Government Agency, Medical Society, and Other Authoritative Publications:

1. Agency for Healthcare Research and Quality (AHRQ). Remote cardiac monitoring. Technology Assessment. ECRI Evidence-based Practice Center (EPC). Contract No. 290-02-0019. Rockville, MD: AHRQ; February  14, 2008. Available at: http://www.cms.hhs.gov/determinationprocess/downloads/id51TA.pdf. Accessed on November 18, 2025.
2. Al-Khatib SM, Stevenson WG, Ackerman MJ, et al. 2017 AHA/ACC/HRS guideline for management of patients with ventricular arrhythmias and the prevention of sudden cardiac death: a report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines and the Heart Rhythm Society. J Am Coll Cardiol. 2018; 72(14):e91-e220.
3. Amsterdam EA, Wenger NK, Brindis RG, et al. American College of Cardiology; American Heart Association Task Force on Practice Guidelines; Society for Cardiovascular Angiography and Interventions; Society of Thoracic Surgeons; American Association for Clinical Chemistry. 2014 AHA/ACC guideline for the management of patients with non-ST-elevation acute coronary syndromes: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines. J Am Coll Cardiol. 2014; 64(24):e139-e228.
4. Blomstrom-Lundqvist C, Scheinman MM, Aliot EM, et al. European Society of Cardiology Committee, NASPE-Heart Rhythm Society. ACC/AHA/ESC guidelines for the management of patients with supraventricular arrhythmias--executive summary. A report of the American College of Cardiology/American Heart Association Task Force on practice guidelines and the European Society of Cardiology Committee for practice guidelines (writing committee to develop guidelines for the management of patients with supraventricular arrhythmias) developed in collaboration with NASPE-Heart Rhythm Society. J Am Coll Cardiol. 2003; 42(8):1493-1531.
5. Brignole M, Moya A, de Lange FJ, et al. 2018 ESC Guidelines for the diagnosis and management of syncope. Eur Heart J. 2018; 39(21):1883-1948.
6. Brignole M, Vardas P, Hoffman E, et al. European Society of Cardiology (EHRA). Position Paper: indications for the use of diagnostic implantable and external ECG loop recorders. Europace. 2009; 11(5):671-687.
7. Calkins H, Hindricks G, Cappato R, et al. 2017 HRS/EHRA/ECAS/APHRS/SOLAECE expert consensus statement on catheter and surgical ablation of atrial fibrillation. Heart Rhythm. 2017; 14(10):e275-e444.
8. Centers for Medicare and Medicaid Services. National Coverage Determination for Electrocardiographic (EKG) Services. NCD #20.15. Effective date: August 26, 2004. Available at https://www.cms.gov/medicare-coverage-database/details/ncd-details.aspx?NCDId=179&ncdver=2&bc=AgAAgAAAAAAA&

Accessed on November 18, 2025.

9. Crawford MH, Bernstein SJ, Deedwania PC, et al. ACC/AHA guidelines for ambulatory electrocardiography: executive summary and recommendations. A report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Committee to revise the Guidelines for Ambulatory Electrocardiography). Circulation. 1999; 100(8):886-893.
10. Culebras A, Messe SR, Chaturvedi S, et al. Summary of evidence-based guideline update: prevention of stroke in nonvalvular atrial fibrillation: report of the Guideline Development Subcommittee of the American Academy of Neurology. Reaffirmed October 22, 2022. Neurology. 2014; 82(8):716-724.
11. Erickson CC, Salerno JC, Berger S, et al. Section On Cardiology and Cardiac Surgery, Pediatric and Congenital Electrophysiology Society (PACES) Task Force on Prevention of Sudden Death in the Young. Sudden death in the young: information for the primary care provider. Pediatrics. 2021; 148(1):e2021052044.
12. Fuster V, Rydén LE, Cannom DS, et al. ACC/AHA/ESC 2006 guidelines for the management of patients with atrial fibrillation: executive summary: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines and the European Society of Cardiology Committee for Practice Guidelines and Policy Conferences (Writing Committee to Revise the 2001 Guidelines for the Management of Patients With Atrial Fibrillation): developed in collaboration with the European Heart Association and the Heart Rhythm Society. Circulation. 2006; 114(7):e257-e354.
13. Fuster V, Ryden LE, Cannom DS, et al. 2011 ACCF/AHA/HRS focused updates incorporated into the ACC/AHA/ESC 2006 guidelines for the management of patients with atrial fibrillation: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines and the European Society of Cardiology Committee for Practice Guidelines. J Am Coll Cardiol. 2011; 57(11):101-198.
14. Gersh BJ, Maron BJ, Bonow RO, et al. American College of Cardiology/American Heart Association (ACCF/AHA) Task Force on Practice Guidelines. 2011 ACCF/AHA guideline for the diagnosis and treatment of hypertrophic cardiomyopathy: a report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines. Developed in collaboration with the American Association for Thoracic Surgery, American Society of Echocardiography, American Society of Nuclear Cardiology, Heart Failure Society of America, Heart Rhythm Society, Society for Cardiovascular Angiography and Interventions and Society of Thoracic Surgeons. J Am Coll Cardiol. 2011; 58(25):e212-e260.
15. Health Quality Ontario. Long-term continuous ambulatory ECG monitors and external cardiac loop recorders for cardiac arrhythmia: a Health Technology Assessment. Ont Health Technol Assess Ser. 2017; 17(1):1-56.
16. Hindricks G, Potpara T, Dagres N, et al. 2020 ESC Guidelines for the diagnosis and management of atrial fibrillation developed in collaboration with the EACTS. Eur Heart J. 2021; 42(5):373-498.
17. Joglar, J, Chung, M. et al. 2023 ACC/AHA/ACCP/HRS Guideline for the diagnosis and management of atrial fibrillation: a report of the American College of Cardiology/American Heart Association Joint Committee on clinical practice guidelines. J Am Coll Cardiol. 2024; 83 (1) 109-279.
18. January CT, Wann LS, Alpert JS, et al. 2014 AHA/ACC/HRS Guideline for the management of patients with atrial fibrillation: executive summary. Circulation. 2014; 130(23):2071-2104.
19. January CT, Wann LS, Calkins H, et al. 2019 AHA/ACC/HRS focused update of the 2014 AHA/ACC/HRS Guideline for the management of patients with atrial fibrillation: a report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines and the Heart Rhythm Society. J Am Coll Cardiol. 2019; 74(1):104-132.
20. Kadish AH, Buxton AE, Kennedy HL, et al. American College of Cardiology/American Heart Association/American College of Physicians-American Society of Internal Medicine Task Force; International Society for Holter and Noninvasive Electrocardiology. ACC/AHA clinical competence statement on electrocardiography and ambulatory electrocardiography: a report of the ACC/AHA/ACP-ASIM task force on clinical competence (ACC/AHA Committee to develop a clinical competence statement on electrocardiography and ambulatory electrocardiography) endorsed by the International Society for Holter and Noninvasive Electrocardiology. Circulation. 2001; 104(25):3169-3178.
21. Kahwati L, MD, MPH; Asher G, MD, MPH; Kadro Z, ND. Evidence summary: Atrial fibrillation: screening, recommendations made by the USPSTF. JAMA. 2022; 327(4):368-383.
22. Kernan WN, Ovbiagele B, Black HR, et al. American Heart Association Stroke Council, Council on Cardiovascular and Stroke Nursing, Council on Clinical Cardiology, and Council on Peripheral Vascular Disease. Guidelines for the prevention of stroke in patients with stroke and transient ischemic attack: a guideline for healthcare professionals from the American Heart Association/American Stroke Association. Stroke. 2014; 45(7):2160-2236.
23. Khairy P, Van Hare GF, Balaji S, et al. PACES/HRS Expert Consensus Statement on the Recognition and management of arrhythmias in adult congenital heart disease. Heart Rhythm. 2014; 11(10):e102-165.
24. Kleindorfer DO, Towfighi A, Chaturvedi S, et al. 2021 guideline for the prevention of stroke in patients with stroke and transient ischemic attack: a guideline from the American Heart Association/American Stroke Association. Stroke. 2021; 52(7):e364-e467.
25. Kusumoto FM, Schoenfeld MH, Barrett C, et al. 2018 ACC/AHA/HRS guideline on the evaluation and management of patients with bradycardia and cardiac conduction delay: a report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines and the Heart Rhythm Society. J Am Coll Cardiol. 2019; 74(7):e51-e156.
26. Medtronic Bakken Research Center. CARISMA: Cardiac Arrhythmias and Risk Stratification After MyoCardial Infarction. NCT00145119. Last updated November 26, 2018. Available at: http://www.clinicaltrials.gov/ct2/show/NCT00145119?term=NCT00145119.&rank=1. Accessed on November 18, 2025.
27. Medtronic Cardiac Rhythm Disease Management/Medtronic Bakken Research Center. Study of Continuous Cardiac Monitoring to Assess Atrial Fibrillation After Cryptogenic Stroke (CRYSTAL-AF). NCT 00924638. Last updated July 28, 2014. Available at: http://clinicaltrials.gov/show/NCT00924638. Accessed on November 18, 2025.
28. Murphy R, Waters R, Murphy A, et al. Risk-based screening for the evaluation of atrial fibrillation in general practice (R-BEAT): a randomized cross-over trial. QJM. 2025; 118(3):166-173.
29. Moya A, Sutton R, Ammirati F, et al.; European Society of Cardiology (ESC); European Heart Rhythm Association (EHRA); Heart Failure Association (HFA); Heart Rhythm Society (HRS), Task Force for the Diagnosis and Management of Syncope. Guidelines for the diagnosis and management of syncope. Updated 2009. Eur Heart J. 2009; 30(21):2631-2671.
30. Ommen SR, Mital S, Burke MA, et al. 2020 AHA/ACC Guideline for the diagnosis and treatment of patients with hypertrophic cardiomyopathy: executive summary: a report of the American College of Cardiology/American Heart Association Joint Committee on clinical practice guidelines. J Am Coll Cardiol. 2020; 76(25):3022-3055.
31. Page RL, Joglar JA, Caldwell MA, et al. 2015 ACC/AHA/HRS guideline for the management of adult patients with supraventricular tachycardia: a report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines and the Heart Rhythm Society. J Am Coll Cardiol. 2016; 67(13):e27-e115.
32. Pedersen CT, Kay GN, Kalman J, et al. EP-Europace, UK. EHRA/HRS/APHRS expert consensus on ventricular arrhythmias. Heart Rhythm. 2014; 11(10):e166-e196.
33. Powers WJ, Rabinstein AA, Ackerson T, et al.; American Heart Association Stroke Council. 2018 guidelines for the early management of patients with acute ischemic stroke: a guideline for healthcare professionals from the American Heart Association/American Stroke Association. Stroke. 2018; 49(3):e46-e110.
34. Raviele A, Giada F, Bergfeldt F, et al. Management of patients with palpitations: a position paper from the European Heart Rhythm Association. Europace. 2011; 13(7):920-934.
35. Shen WK, Sheldon RS, Benditt DG, et al. 2017 ACC/AHA/HRS guideline for the evaluation and management of patients with syncope: a report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines, and the Heart Rhythm Society. Heart Rhythm. 2017; 14(8):e218-e254.
36. Spooner MT, Messé SR, Chaturvedi S, et al. 2024 ACC Expert consensus decision pathway on practical approaches for arrhythmia monitoring after stroke: a report of the American College of Cardiology Solution Set Oversight Committee. J Am Coll Cardiol. 2025; 85(6):657-681.
37. Steinberg JS, Varma N, Cygankiewicz I, et al. 2017 International Society for Holter and Noninvasive Electrocardiology and the Heart Rhythm Society (ISHNE-HRS) expert consensus statement on ambulatory ECG and external cardiac monitoring/telemetry. Heart Rhythm. 2017; 14(7):e55-e96.
38. U.S. Food and Drug Administration (FDA). Center for Devices and Radiologic Health. Zio^® Patch. No. K113862. Rockville, MD: FDA. February 6, 2012. Available at: http://www.accessdata.fda.gov/cdrh_docs/pdf11/K113862.pdf. Accessed on November 18, 2025.
39. U.S. Food and Drug Administration (FDA). Center for Devices and Radiologic Health. SimplECG. No. K161431. Rockville, MD: FDA. November 30, 2016. Available at: https://www.accessdata.fda.gov/cdrh_docs/pdf16/K161431.pdf. Accessed on November 18, 2025.

1. American Heart Association. Holter Monitor. Last reviewed February 25, 2025. Available at: https://www.heart.org/en/health-topics/heart-attack/diagnosing-a-heart-attack/holter-monitor. Accessed on November 18, 2025.
2. MedlinePlus. Holter monitor (24h). Reviewed May 27, 2024. Available at: http://www.nlm.nih.gov/medlineplus/ency/article/003877.htm. Accessed on November 18, 2025.

Ambulatory Event Monitors
BodyGuardian Remote Monitoring System^™
Cardiac Arrhythmias
Cardiac Event Monitors/Loop Recorders
Continuous Cardiac Recorder
Holter Monitor
iRhythm Zio Patch
SimplECG Nanowear

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