Ambulatory ECG monitoring in the age of smartphones

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Release date: July 1, 2019
Expiration date: June 30, 2020
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Ambulatory electrocardiography (ECG) allows for extended monitoring of arrhythmias in a real-world setting. This article reviews the currently available ambulatory ECG devices and their differences in design, function, indications, efficacy, cost, and optimal use in clinical practice.


  • Ambulatory ECG monitoring is commonly used to correlate symptoms with arrhythmia, confirm occult atrial fibrillation, and assess the efficacy of antiarrhythmic therapy.
  • Devices have features such as access to the full monitoring time (“full disclosure”), extended monitoring, and telemetry, each with advantages and limitations.
  • Consumer-oriented wearable devices are aimed at arrhythmia monitoring, which could lead to increased arrhythmia detection, but at the risk of more false-positive results and excessive use of healthcare resources.



A mbulatory electrocardiography (ECG) began in 1949 when Norman “Jeff” Holter developed a monitor that could wirelessly transmit electrophysiologic data.1 His original device used vacuum tubes, weighed 85 pounds, and had to be carried in a backpack. Furthermore, it could send a signal a distance of only 1 block.2

At the time, it was uncertain if this technology would have any clinical utility. However, in 1952, Holter published the first tracing of abnormal cardiac electrical activity in a patient who had suffered a posterior myocardial infarction.3 By the 1960s, Holter monitoring systems were in full production and use.4

Since then, advances in technology have led to small, lightweight devices that enable clinicians to evaluate patients for arrhythmias in a real-world context for extended times, often with the ability to respond in real time.

Many ambulatory devices are available, and choosing the optimal one requires an understanding of which features they have and which are the most appropriate for the specific clinical context. This article reviews the features, indications, advantages, and disadvantages of current devices, and their best use in clinical practice.


Table 1. Indications for ambulatory electrocardiography devices
Several guidelines have been published to help practitioners understand the available ambulatory ECG devices and their uses in clinical practice.5,6 The latest, published in 2017 by the International Society for Holter and Noninvasive Electrocardiology and Heart Rhythm Society,6 divided indications for ambulatory cardiac monitoring into 3 broad categories: diagnosis, prognosis, and arrhythmia assessment (Table 1).


The most common diagnostic role of monitoring is to correlate unexplained symptoms, including palpitations, presyncope, and syncope, with a transient cardiac arrhythmia. Monitoring can be considered successful if findings on ECG identify risks for serious arrhythmia and either correlate symptoms with those findings or demonstrate no arrhythmia when symptoms occur.

A range of arrhythmias can cause symptoms. Some, such as premature atrial contractions and premature ventricular contractions, may be benign in many clinical contexts. Others, such as atrial fibrillation, are more serious, and some, such as third-degree heart block and ventricular tachycardia, can be lethal.

Arrhythmia symptoms can vary in frequency and cause differing degrees of debility. The patient’s symptoms, family history, and baseline ECG findings can suggest a more serious or a less serious underlying rhythm. These factors are important when determining which device is most appropriate.

Ambulatory ECG can also be useful in looking for a cause of cryptogenic stroke, ie, an ischemic stroke with an unexplained cause, even after a thorough initial workup. Paroxysmal atrial fibrillation is a frequent cause of cryptogenic stroke, and because it is transient, short-term inpatient telemetry may not be sufficient to detect it. Extended cardiac monitoring, lasting weeks or even months, is often needed for clinicians to make this diagnosis and initiate appropriate secondary prevention.

Prognosis: Identifying patients at risk

In a patient with known structural or electrical heart disease, ambulatory ECG can be used to stratify risk. This is particularly true in evaluating conditions associated with sudden cardiac death.

For example, hypertrophic cardiomyopathy and arrhythmogenic right ventricular dysplasia or cardiomyopathy are 2 cardiomyopathies that can manifest clinically with ventricular arrhythmias and sudden cardiac death. Ambulatory ECG can detect premature ventricular contractions and ventricular tachycardia and identify their frequency, duration, and anatomic origin. This information is useful in assessing risk of sudden cardiac death and determining the need for an implantable cardioverter-defibrillator.

Similarly, Wolff-Parkinson-White syndrome, involving rapid conduction through an accessory pathway, is associated with increased risk of ventricular fibrillation and sudden cardiac death. Ambulatory ECG monitoring can identify patients who have electrical features that portend the development of ventricular fibrillation.

Also associated with sudden cardiac death are the inherited channelopathies, a heterogeneous group of primary arrhythmic disorders without accompanying structural pathology. Ambulatory ECG monitoring can detect transient electrical changes and nonsustained ventricular arrhythmias that would indicate the patient is at high risk of these disorders.

Assessing arrhythmia treatment

Arrhythmia monitoring using an ambulatory ECG device can also provide data to assess the efficacy of treatment under several circumstances.

The “pill-in-the-pocket” approach to treating atrial fibrillation, for example, involves self-administering a single dose of an antiarrhythmic drug when symptoms occur. Patients with infrequent but bothersome episodes can use an ambulatory ECG device to detect when they are having atrial fibrillation, take their prescribed drug, and see whether it terminates the arrhythmia, all without going to the hospital.

Ambulatory ECG also is useful for assessing pharmacologic or ablative therapy in patients with atrial fibrillation or ventricular tachycardia. Monitoring for several weeks can help clinicians assess the burden of atrial fibrillation when using a rhythm-control strategy; assessing the ventricular rate in real-world situations is useful to determine the success of a rate-control strategy. Shortly after ablation of either atrial fibrillation or ventricular tachycardia, ECG home monitoring for 24 to 48 hours can detect asymptomatic recurrence and treatment failure.

Some antiarrhythmic drugs can prolong the QT interval. Ambulatory ECG devices that feature real-time monitoring can be used during drug initiation, enabling the clinician to monitor the QT interval without admitting the patient to the hospital.

Ultimately, ambulatory ECG monitoring is most commonly used to evaluate symptoms. Because arrhythmias and specific symptoms are unpredictable and transient, extended monitoring in a real-world setting allows for a more comprehensive evaluation than a standard 10-second ECG recording.


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