Providing information regarding the onset and resolution of tachyarrhythmias and bradyarrhythmias. Providing information on a variety of arrhythmia characteristics such as coupling interval, rate dependence, and changes in QT interval. Ambulatory monitoring, typically with 24 to 48 hours of continuous ambulatory ECG, is useful for the evaluation of rate control of atrial fibrillation (AF) during daily activities or with exercise in patients who have permanent AF. Ambulatory monitoring may be used to assess AF burden (frequency or episodes and duration of episodes) in patients with paroxysmal or intermittent AF. (See "Control of ventricular rate in patients with atrial fibrillation who do not have heart failure: Pharmacologic therapy", section on 'Evaluation and goal ventricular rate'.) FOLLOW-UP AFTER AMBULATORY ECG MONITORING After the diagnostic monitoring period, the following scenarios of patient symptoms and ECG findings might be encountered: The patient had symptoms with corresponding ECG abnormalities (ie, arrhythmia or conduction abnormality) Such patients should be treated appropriately and, in most https://www.uptodate.com/contents/ambulatory-ecg-monitoring/print 13/26 7/6/23, 10:40 AM Ambulatory ECG monitoring - UpToDate instances, do not require additional ambulatory ECG monitoring for diagnostic purposes (although additional monitoring to assess the efficacy of therapy might be indicated). The patient had symptoms without corresponding ECG abnormalities (ie, arrhythmia or conduction abnormality) In such instances, assuming that the monitor was functioning properly and the available ECG data are interpretable, the diagnosis is likely non-cardiac and there is generally no need for additional ambulatory ECG monitoring. The patient had no symptoms and no ECG abnormalities during the monitoring period The decision to pursue additional testing following a period of ambulatory ECG monitoring depends on the potential severity of the clinical conditions. As examples: A patient who experiences only infrequent and mild palpitations who had an unremarkable four-week event monitor can usually be managed conservatively. Conversely, a patient with more severe symptoms might require more prolonged ambulatory ECG monitoring to make a diagnosis (such as with an insertable cardiac monitor [ICM]). For a patient with history of cryptogenic stroke who had an unremarkable four-week event monitor for whom a diagnosis of atrial fibrillation would prompt the need for stroke prevention therapy (ie, initiation of oral anticoagulation), prolonged ambulatory ECG monitoring should be instituted (such as with an ICM). A patient who has suffered syncope (particularly abrupt syncope without warning symptoms that resulted in injury) but who did not have recurrent symptoms or ECG abnormalities during the initial monitoring should usually proceed with prolonged ambulatory ECG monitoring (such as with an ICM). SOCIETY GUIDELINE LINKS Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Arrhythmias in adults" and "Society guideline links: Ventricular arrhythmias" and "Society guideline links: Atrial fibrillation" and "Society guideline links: Supraventricular arrhythmias".) SUMMARY AND RECOMMENDATIONS Background In contrast to the standard electrocardiogram (ECG), which provides a brief sample of cardiac electrical activity over 10 seconds, ambulatory ECG monitoring provides a https://www.uptodate.com/contents/ambulatory-ecg-monitoring/print 14/26 7/6/23, 10:40 AM Ambulatory ECG monitoring - UpToDate view of ECG data over an extended period of time, thereby permitting evaluation of dynamic and transient cardiac electrical phenomena. (See 'Introduction' above.) Indications Ambulatory ECG monitoring is the most widely employed technology to evaluate a patient with symptoms suggestive of a cardiac arrhythmia or a conduction abnormality (ie, unexplained syncope/near syncope or unexplained palpitations), but it is also used for a variety of other diagnostic and prognostic indications. (See 'Indications' above.) Types of monitors Ambulatory ECG monitoring is available in many forms ( table 2), including continuous (Holter) monitoring for 24 to 48 hours ( figure 1), event (loop) monitoring for several weeks, or insertable cardiac monitoring ( picture 2) for months to years. (See 'Types of ambulatory ECG monitoring' above.) The approach to choosing an ambulatory ECG monitoring strategy depends on the indication for the test along with the frequency and duration of symptoms ( table 1). If an ambulatory ECG monitor is being used for diagnostic purposes (ie, unexplained syncope or unexplained palpitations), extended duration monitoring might be required to increase the diagnostic yield. (See 'Diagnostic efficacy' above and 'Our approach to choosing an ambulatory ECG monitoring strategy' above.) Importance of symptom correlation The ECG rhythm recorded using any ambulatory ECG monitoring modality should be correlated with the simultaneous occurrence of suggestive symptoms. (See 'Diagnostic efficacy' above.) ACKNOWLEDGMENT The editorial staff at UpToDate acknowledge Philip Podrid, MD, who contributed to an earlier version of this topic review. Use of UpToDate is subject to the Terms of Use. REFERENCES 1. Boudoulas H, Schaal SF, Lewis RP, Robinson JL. Superiority of 24-hour outpatient monitoring over multi-stage exercise testing for the evaluation of syncope. J Electrocardiol 1979; 12:103. 2. Poblete PF, Kennedy HL, Caralis DG. Detection of ventricular ectopy in patients with coronary heart disease and normal subjects by exercise testing and ambulatory electrocardiography. Chest 1978; 74:402. https://www.uptodate.com/contents/ambulatory-ecg-monitoring/print 15/26 7/6/23, 10:40 AM Ambulatory ECG monitoring - UpToDate 3. Steinberg JS, Varma N, Cygankiewicz I, et al. 2017 ISHNE-HRS expert consensus statement on ambulatory ECG and external cardiac monitoring/telemetry. Heart Rhythm 2017; 14:e55. 4. Crawford MH, Bernstein SJ, Deedwania PC, et al. 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Topic 958 Version 40.0 https://www.uptodate.com/contents/ambulatory-ecg-monitoring/print 18/26 7/6/23, 10:40 AM Ambulatory ECG monitoring - UpToDate GRAPHICS Table ambulatory electrocardiographic monitoring clinical scenarios Ambulatory ECG monitor type Indications/patient selection Continuous ECG monitor (ie, Holter monitor) Daily or near daily symptoms (palpitations) Assessment for adequate rate control in atrial fibrillation Assessment of VPB or APB burden, NSVT in hypertrophic cardiomyopathy Heart rate assessment for inappropriate sinus tachycadia, postural orthostatic tachycardia syndrome, suspected chronotropic incompetence Event (loop) monitor Less frequent symptoms (weekly or biweekly) Assessment for arrhythmic source of palpitations Assessment for arrhythmic source of dizziness or pre- syncope/syncope Assessment for atrial fibrillation (though asymptomatic episodes could be missed unless an auto-triggered event monitor is used) Patch monitor Daily, near daily, or weekly frequency of symptoms Assess arrhythmia burden (eg, atrial fibrillation, VPBs) Assess for NSVT in hypertrophic cardiomyopathy Assessment for atrial fibrillation as a source of cryptogenic stroke (diagnosis limited by length of time the monitor is worn) Mobile cardiac outpatient telemetry (MCOT) Assess arrhythmia burden (eg, atrial fibrillation, VPBs) Assessment for arrhythmic source of palpitations Assessment for arrhythmic source of dizziness or pre- syncope/syncope Assessment for atrial fibrillation as a source of cryptogenic stroke (diagnosis limited by length of time the monitor is worn) Implantable loop recorder Infrequent (less than monthly) symptoms associated with syncope or other high risk features Assessment for atrial fibrillation as a source of cryptogenic stroke Assessment for recurrence of atrial fibrillation (eg, post- ablation) https://www.uptodate.com/contents/ambulatory-ecg-monitoring/print 19/26 7/6/23, 10:40 AM Ambulatory ECG monitoring - UpToDate Commercially available heart rate monitor (eg, wristbands, smartwatches) No approved indications Commercially available heart rhythm monitors (eg, smartwatches, hand held devices, smartphone based electrode cards, etc) No approved indications Can be considered for monitoring for arrhythmic source or palpitations Can be considered for monitoring for symptomatic atrial fibrillation recurrence Clinical monitoring scenarios Available monitoring options Symptoms (palpitations) daily or near daily Continuous ECG monitor (Holter) Patch monitor Symptoms (palpitations) weekly or biweekly Event (loop) monitor Patch monitor MCOT Symptoms infrequently (monthly or less) associated with syncope or high Implantable loop recorder risk features Assessment for occult atrial fibrillation* Event (loop) monitor, ideally an auto-triggered event monitor Patch monitor MCOT Implantable loop recorder Assessment for arrhythmia burden (eg, VPB burden) or average heart rate (eg, AF, inappropriate sinus tachycardia, etc) Continuous ECG monitor (Holter) Patch monitor MCOT ECG: electrocardiogram; VPB: ventricular premature beats; APB: atrial premature beats; NSVT: nonsustained ventricular tachycardia; AF: atrial fibrillation. Notably, the longer the monitoring duration, the higher the diagnostic yield. Adapted from: 1. 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. J Am Coll Cardiol 2017; 70:e39. 2. 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 2018. Graphic 120898 Version 3.0 https://www.uptodate.com/contents/ambulatory-ecg-monitoring/print 20/26 7/6/23, 10:40 AM Ambulatory ECG monitoring - UpToDate Table ambulatory electrocardiographic monitoring capabilities Ambulatory ECG Monitor capabilities monitor type Continuous ECG monitor (ie, Record all ECG data for 24 to 48 hours Holter monitor) Off-line analysis and review following completion of recording Typically 3 ECG leads but 12-lead options available Patient diary to record symptoms, with time correlation to ECG rhythm Event (loop) monitor Records one or two lead ECG data around time of arrhythmias May be triggered automatically in response to program settings or by patient following symptoms May be worn continuously or applied during symptoms May be worn for up to 30 days ECG data for triggered events can be sent wirelessly for real-time analysis to central monitoring station that can alert physicians and be made available for on-line review Patch monitor Records single-lead ECG data continuously (3, 7, 14, or 30 days) May be triggered automatically in response to program settings or by patient following symptoms Traditional off-line analysis at central monitoring station following completion of recording that is then available for on-line review by physicians Some models have capability to wirelessly transmit ECG data for triggered events for real-time analysis to central monitoring station that can alert physicians and be made available for on-line review Mobile cardiac outpatient telemetry (MCOT) Traditionally 3 leads but now also available in patch form (single lead) Can be worn for up to 30 days with continuous recording May be triggered automatically in response to program settings or by patient following symptoms Daily report is transmitted wirelessly to central monitoring station and is made available on-line for physician review ECG data for triggered events can be sent wirelessly for real-time analysis to central monitoring station that can alert physicians and be made available for on-line for review Implantable loop recorder Subcutaneously implanted, available for monitoring up to several years Triggered automatically or by patient/witness for symptomatic events https://www.uptodate.com/contents/ambulatory-ecg-monitoring/print 21/26 7/6/23, 10:40 AM Ambulatory ECG monitoring - UpToDate Commercially available heart Photoplethysmography technology records heart rate rate monitor (eg, wristbands, smartwatches) Data can be stored on smartphones, tablets/lap tops, or directly on devices Some devices have algorithms to detect rhythm/rate irregularities and alert for possible atrial fibrillation Commercially available heart rhythm monitors (eg, Single-lead ECG data that is recorded by patient during symptoms Some devices have algorithms to detect heart rhythm irregularities such as atrial fibrillation smartwatches, hand held devices, smartphone based electrode cards, etc) Rhythm strips can be stored on smart phones or directly on hand held devices and shared with physicians for review ECG: electrocardiogram Adapted from: 1. 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. J Am Coll Cardiol 2017; 70:e39. 2. 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 2018. Graphic 120899 Version 3.0 https://www.uptodate.com/contents/ambulatory-ecg-monitoring/print 22/26 7/6/23, 10:40 AM Ambulatory ECG monitoring - UpToDate Ambulatory (Holter) electrocardiography (ECG) monitor The ambulatory (Holter) monitor is a lightweight continuous electrocardiographic (ECG) monitoring system that uses three surface electrodes to continuously record all cardiac electrical activity, typically for 24 to 48 hours. Once the monitoring period is over, the patient returns the device, and all of the acquired data are analyzed (usually by a trained technician) and a summary report is generated for clinician review. Graphic 105244 Version 1.0 https://www.uptodate.com/contents/ambulatory-ecg-monitoring/print 23/26 7/6/23, 10:40 AM Ambulatory ECG monitoring - UpToDate Torso with Zio Reproduced with permission from: iRhythm Technologies, Inc. Copyright 2019. Available at: https://www.irhythmtech.com/products-services/zio-xt (Accessed on May 10, 2019). Graphic 121242 Version 1.0 https://www.uptodate.com/contents/ambulatory-ecg-monitoring/print 24/26 7/6/23, 10:40 AM Ambulatory ECG monitoring - UpToDate Insertable cardiac monitors (ICMs) for long- term electrocardiographic (ECG) monitoring Photograph showing two examples of insertable cardiac monitors used for long-term electrocardiographic (ECG) monitoring. The device is typically inserted under local anesthesia in the left anterior chest. Though not pictured, a third device from a different manufacturer (Biotronik) is available for clinical use. Graphic 104724 Version 4.0 https://www.uptodate.com/contents/ambulatory-ecg-monitoring/print 25/26 7/6/23, 10:40 AM Ambulatory ECG monitoring - UpToDate Contributor Disclosures Christopher Madias, MD No relevant financial relationship(s) with ineligible companies to disclose. Peter J Zimetbaum, MD Consultant/Advisory Boards: Abbott Medical [Lead extraction]. All of the relevant financial relationships listed have been mitigated. Nisha Parikh, MD, MPH No relevant financial relationship(s) with ineligible companies to disclose. Contributor disclosures are reviewed for conflicts of interest by the editorial group. When found, these are addressed by vetting through a multi-level review process, and through requirements for references to be provided to support the content. Appropriately referenced content is required of all authors and must conform to UpToDate standards of evidence. Conflict of interest policy https://www.uptodate.com/contents/ambulatory-ecg-monitoring/print 26/26