Abstract

Recent landmark trials provided the impetus to update the recommendations for cardiac resynchronization therapy (CRT). This article pro- vides guidance on the prescription of CRT within the confines of published data. A future article will explore the implementation of these guidelines. These guidelines are intended to serve as a framework for the prescription of CRT within the Canadian health care system and beyond. They were developed through a critical evaluation of the existing literature, and expert consensus. The panel unanimously adopted each recommendation. The 8 recommendations relate to ensuring the adequacy of medical therapy before the initiation of CRT, the use of symptom severity to select candidates for CRT, differing recommendations based on the presence or absence of sinus rhythm, the presence of left bundle branch block vs other conduction patterns, and QRS duration. The use of CRT in the setting of chronic right ventricular pacing, left ventricular lead placement, and the routine assessment of dyssynchrony to guide the prescription of CRT are also included. The strength of evidence was weighed, taking full consideration of any risks of bias, as well as any imprecision, inconsistency, and indirectness of the available data. The strength of each recommendation and the quality of evidence were adjudicated. Trade- offs between desirable and undesirable consequences of alternative management strategies were considered, as were values, preferences, and resource availability. These guidelines were externally reviewed by experts, modified based on those reviews, and will be updated as new knowledge is acquired.

Introduction

Rationale for cardiac resynchronization therapy:

Heart failure affects more than 485,000 Canadians and results in significant morbidity and mortality.1 Despite advances in medical therapy, patients with heart failure remain at high risk for death and hospitalization.1 Dyssynchronous ventricular contraction affects 1 in 4 patients with systolic heart failure. Cardiac resynchronization therapy (CRT) is designed to synchronize the mechanical activity of the ventricles, and the timing of the atria and ventricles among those in sinus rhythm. QRS duration, along with functional class and left ventricular ejection fraction (LVEF), are used to select candidates for CRT. Among selected patients, CRT has been shown to improve left ventricular (LV) function (reverse remodelling), reduce mitral regurgitation, enhance cardiac output, and reduce heart failure symptoms without increasing myocardial energy consumption. Improved cardiac mechanical synchrony is thought to be central to the benefit of CRT. Improved survival and reduced morbidity have been demonstrated among selected patients with systolic heart failure enrolled in large randomized trials of CRT.