Syncope is a common condition with an estimated lifetime prevalence of 35%.² Finding the underlying cause of syncope can be challenging and requires a detailed history and physical examination. The most useful information, however, may be difficult to obtain during patient encounters unless the patient has active symptomatic episodes.³

Ambulatory monitoring plays a key role in diagnosing underlying cardiac arrhythmias that may occur during symptomatic episodes. The selection of an ambulatory monitoring device depends primarily on the predicted duration of the monitoring period needed to capture a symptomatic event. Patients may be placed on a Holter monitor, an extended Holter monitor (EHM), or an event monitor. Inconclusive studies with recurrent episodes may warrant more long-term monitoring such as an implantable loop recorder. The advantages and disadvantages of the different monitoring methods are discussed later in the chapter.

Identifying underlying cardiac arrhythmias can have significant implications for patient outcomes. In elderly patients with unexplained falls, as many as 20% of patients with an implantable loop recorder can be found to have an arrhythmia as the etiology of their falls.⁴

Palpitations can be due to various arrhythmias that cause noticeable change, acceleration, or irregularity in heart rhythm noticed by patients. A common cause of palpitations is atrial fibrillation (AF) with a rapid ventricular rate. Ambulatory monitoring is often recommended, with the choice of modality dependent on the frequency of the symptomatic episodes when AF is suspected. Automated algorithms have improved detection of AF with a high degree of sensitivity and specificity.⁵

Initiation of antiarrhythmic drugs for patients may warrant a period of ambulatory monitoring to evaluate the efficacy of therapy. For example, in a patient with symptomatic premature ventricular complexes (PVCs), ambulatory monitoring can help quantify burden before and after initiation of antiarrhythmic medications to determine treatment effect. According to the American Heart Association/American College of Cardiology (AHA/ACC) guidelines, for a patient with an
underlying arrhythmia with confirmed reproducibility, initiating an antiarrhythmic medication would warrant ambulatory monitoring.⁶

Several congenital conditions, such as Brugada syndrome and congenital long-QT syndrome, may predispose an individual to developing ventricular arrhythmias (VAs). Ambulatory monitoring can help guide risk stratification and associated medical/interventional therapy for management of VAs.

In patients with Wolff-Parkinson-White syndrome, ambulatory monitoring may also play a role in risk stratification.⁷ Electrocardiographic (ECG) monitoring can identify the heart rate at which preexcitation is lost, generally correlating with the risk of developing life-threatening VA.⁸ Because the demographic of preexcitation pathways commonly affect younger patients, ambulatory monitoring may guide risk-benefit discussions regarding subsequent participation in sports and the need for further evaluation with an electrophysiology study and catheter ablation.

Patients with arrhythmias refractory to medical treatment may be candidates for ablation procedures. These include the spectrum of arrhythmias from supraventricular tachycardias (SVTs) to VAs. For these patients, ambulatory monitoring can provide an assessment of the characteristics of the specific arrhythmia, the arrhythmia burden, and elucidating morphology (P wave or QRS complex) suggestive of anatomic origin.

PVCs occur sporadically in most healthy individuals; however, with increased frequency, they may be associated with PVC-induced cardiomyopathy and poorer cardiovascular outcomes.⁹ Ambulatory monitoring helps assess the burden of PVCs in patients, and guides further management regarding medical therapy or potential ablative management. Furthermore, the morphologies of the PVCs help localize the site of origin for the ablation procedure.¹⁰

AF is the most common arrhythmia in the United States and Europe. Patient symptom profiles can vary, and may not accurately represent the amount of time a patient spends in AF. Ambulatory monitoring may help in distinguishing persistent (ie, occurs for longer than 7 days) versus paroxysmal (lasts <1 week) AF, and aid in discussions regarding risk, prognosis, and procedural outcomes.¹¹ Catheter ablation success rates for paroxysmal AF are estimated at 70% to 80%, whereas for persistent AF, ablation provides 30% to 60% success.¹²,¹³ Because AF has been shown to progress from paroxysmal to persistent to permanent in a subset of patients, ambulatory monitoring may also help monitor the AF burden in patients over time.

Inherited cardiomyopathies such as hypertrophic cardiomyopathy (HCM) or arrhythmogenic right ventricular cardiomyopathy (ARVC) place patients at high risk for sudden cardiac death (SCD). HCM is one of the most common inherited cardiac disorders worldwide, and is associated with increased risk of SCD in young adulthood. Approximately 20% of adults with HCM have non-sustained ventricular tachycardia (NSVT), which is associated with increased risk of SCD. Ambulatory monitoring is thus recommended as part of the initial evaluation of patients with HCM.¹⁴ Similarly, in patients with suspected ARVC, the presence of VA forms part of the diagnostic criteria, so ambulatory monitoring should be obtained in patients undergoing evaluation for ARVC.¹⁵ Furthermore, any symptoms such as palpitations, presyncope, or syncope would warrant additional monitoring of patients with high-risk cardiomyopathies. This data may then be used to risk stratify patients and assess the need for implantable cardioverter-defibrillator (ICD) placement.¹⁴,¹⁶,¹⁷