Ambulatory electrocardiogram (ECG) monitors are often used to detect, document, and characterize abnormal electrical activity during daily activities.¹ It should be emphasized that ambulatory ECG monitoring is noninvasive, easy to use, relatively inexpensive, and readily available compared to other medical devices. The latest achievements in ambulatory ECG are remarkable. What was considered impossible just 10 years ago has become possible now. Currently, ambulatory ECG recordings can be performed with 12-lead formats. This standard 12-lead format utilizes 10 electrodes to measure resting ECG and permits recording periods up to 4 consecutive weeks with loop function. Furthermore, continuous wearable recorders such as belts, vests, or patch ECG monitors and mobile cardiac telemetry (external real-time
cardiac telemonitoring system with wireless transmission) are available to detect symptomatic arrhythmias. Additionally, specific analyses using ambulatory ECG recordings have been performed to predict future arrhythmic events and/or sudden cardiac death (SCD). Thus, modern ambulatory ECG monitoring has numerous characteristics and advantages in clinical practice. In this chapter, current and future needs with respect to ambulatory ECG monitoring techniques and systems are introduced and discussed.

Ambulatory ECG is generally performed in the diagnosis and assessment of potential arrhythmias or conduction disturbances, but it is difficult to use as a diagnostic tool for cardiac disorders because the most common systems have only one to three channels. However, when the ambulatory (Holter) systems have 12 channels and are used for 24 to 48 hours, it could be useful as a diagnostic tool.² This tool could be particularly useful for diagnosing transient or silent myocardial ischemia and dynamic electrical disorders that occur quickly, such as Brugada syndrome. An ECG of myocardial ischemia would identify the location of ischemia or culprit coronary artery. In fact, it has been reported that continuous or ambulatory 12-lead ECG monitoring has potential utility in the diagnosis of postoperative peripheral vascular diseases and asymptomatic myocardial ischemia after peripheral vascular surgery³ and for the detection of a typical ECG pattern of patients in whom Brugada syndrome is suspected.⁴,⁵ The Holter 12-lead ECG system makes use of 10 electrodes (Figure 17.1), as do the standard 12-lead ECG systems. A double-blinded study has demonstrated that Holter 12-lead ECGs recorded in a controlled environment are not significantly different, but more variable, than those from the standard 12-lead ECG method.⁶ In the future, Holter 12-lead ECG monitoring systems will be used in the evaluation of interventional therapeutic procedures or the effect of cardiovascular medicines. In addition, its monitoring will be efficient to localize the origin of ventricular tachyarrhythmias.

Recently, ambulatory ECG monitoring has been utilized to identify individuals with undiagnosed atrial fibrillation (AF) who could benefit from treatment to reduce their risk of serious adverse events. It is well known that AF is a main cause of ischemic stroke (cerebral embolism). Patients diagnosed as having a cryptogenic stroke or embolic stroke of undetermined source (ESUS) sometimes appear normal on standard ECG tests, including 24-hour Holter ECG monitoring. Continuous ambulatory ECG monitoring, however, would increase the detection rate of transient (paroxysmal) AF. In fact, recent studies have reported that noninvasive ambulatory ECG monitoring (event-triggered recorder) with a 30-day recording period significantly improved the detection of AF in patients with ESUS.⁷ In these patients, oral anticoagulation therapy is strongly recommended; otherwise, it is contraindicated to prevent recurrent ischemic stroke. However, as shown in a recent study,⁸ long-term ECG monitoring with an insertable cardiac monitor would achieve higher detection rates of undiagnosed AF.