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Kusumoto et al 2018 Bradycardia Clinical Practice Guidelines

August 20, 2019 Circulation. 2019;140:e382–e482. DOI: 10.1161/CIR.0000000000000628 e388

CLINICAL STATEMENTS AND GUIDELINES 1.6 Abbreviations

Abbreviation Meaning/Phrase ACHD adult congenital heart disease AF atrial fibrillation CIED cardiovascular implantable electronic devices CRT cardiac resynchronization therapy HV His-ventricular ICD implantable cardioverter defibrillator ICM implantable cardiac monitor ECG electrocardiogram EPS electrophysiology study LBBB left bundle branch block LVEF left ventricular ejection fraction MI myocardial infarction MRI magnetic resonance imaging PPM permanent pacemaker QOL quality of life RBBB right bundle branch block RCT randomized controlled trial RV right ventricle SACT sinoatrial conduction time SND sinus node dysfunction SNRT sinus node recovery time TAVR transcatheter aortic valve replacement

2 EPIDEMIOLOGY AND DEFINITIONS

2.1 Bradycardia and Conduction

Disorders

Because slower heart rates and changes in intercellular conduction can be observed as both part of normal aging and disease progression, bradycardia and conduction abnormalities are more commonly identified in the elderly. Abnormalities of the sinus node, atrial tissue, atrioventricular nodal tissue, and the specialized conduction system can all contribute to bradycardia, discordant timing of atrial and ventricular depolarization, and abnormal ventricular depolarization. Sinus node dysfunction (SND), historically referred to as sick sinus syndrome, is most often related to age-dependent, progressive, degenerative fibrosis of the sinus nodal tissue and surrounding atrial myocardium.S2.1-1– S2.1-3 This can result in abnormalities of sinus node and atrial impulse formation and propagation and can be associated with various bradycardia or pause-related syndromes. In addition, the same milieu of degenerative fibrosis is also responsible for the development of atrial arrhythmias, which can coexist with sinus node disease and the combination often called “tachy-brady syndrome.” There is evidence that heart block occurs in a portion of patients who have required permanent atrial pacing for SND, suggesting that, in some patients, a similar fibrotic process likely involves the specialized atrioventricular conduction system.S2.1-3,S2.1-4 Data gathered from permanent pacemaker (PPM) studies and the large cohort studies of ARIC (Atherosclerosis Risk In Communities) and CHS (Cardiovascular Health Study) suggest that SND is most common in individuals who are in their 70s or 80s.S2.1-5–S2.1-7 SND appears to mirror the incidence of pacemaker implantation for atrioventricular nodal disease because both are age related.S2.1-7 In these analyses, ischemic heart disease, heart failure, valvular heart disease, cerebrovascular disease, and atrial fibrillation (AF) were found to be common concurrent issues in this subgroup of patients who require treatment for their atrioventricular nodal disease.S2.1-5–S2.1-7 The intrinsic sinus and atrioventricular nodal diseases present in a similar clinical manner to extrinsic/secondary processes that can injure the sinus node, atrioventricular node or conduction system tissues. Multiple pathophysiologic processes (eg, myocardial ischemia or infarction, infiltrative diseases, collagen vascular disease, surgical trauma, endocrine abnormalities, autonomic effects, neuromuscular disorders,S2.1-2,S2.1-8–S2.1-10 individually or in combination, can compromise impulse initiation and propagation. Whether intrinsic or extrinsic, the clinical manifestations of these pathologies can be identical.

2.2 Definitions

The National Institutes of Health defines bradycardia as a heart rate <60 bpm in adults other than well trained athletes.S2.2-1 However, population studies frequently use a lower cutoff of 50 bpm.S2.2-2,S2.2-3 In an analysis of 4 population studies from the Netherlands, in adults from 20 to 90 years of age, the lowest second percentile for heart rate ranged from 40 to 55 bpm depending on sex and age.S2.2-3 Sinus pauses of 2 seconds and 3 seconds have been described during 24-hour ambulatory electrocardiographic monitoring in healthy elderly patients and long-distance runners, respectively.S2.2-4,S2.2-5 On the basis of the available evidence, for the purposes of this document, we have chosen a sinus rate <50 bpm and/ or a sinus pause >3 seconds as potential components of the definitions of SND. However, the presence of sinus bradycardia or a pause >3 seconds alone should not be used for the diagnosis of SND; multiple factors should be recognized and be taken into consideration for the individual patient (Table 3). With rare exceptions, the sole reason for considering any treatment for SND is the presence of symptoms. Chronotropic incompetence represents failure to reach a target heart rate with exertion relative to expected for age that is inadequate to meet metabolic demand. Because the incremental heart rate achieved with exercise will be dependent on resting heart rate,

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