ABSTRACT
Over the past decade, cardiac resynchronization therapy (CRT) has evolved as an important treatment option for many patients with chronic heart failure who have remained symptomatic despite optimization of pharmacologic therapy. More than 10 years ago, observational studies provided the feasibility and acute hemodynamic data necessary to support proof of concept for CRT (Table 5.1). Over the past 5 years, more than 4000 patients have participated in randomized clinical trials that have validated the effectiveness of CRT in present-day clinical practice. These trials have evolved from relatively small studies utilizing a crossover design to assess various measures of functional status to larger trials with parallel control groups and composite endpoints including outcomes such as cardiac mortality, all-cause mortality, and heart failure hospitalizations. Completed clinical trials to date have provided convincing data supporting the efficacy of CRT in patients meeting a relatively narrow set of inclusion criteria including optimal medical therapy for heart failure, New York Heart Association (NYHA) classes III and IV, decreased left ventricular ejection fraction (LVEF) 35%, increased QRS duration, sinus rhythm, and biventricular pacing configuration. When patients have met these criteria, randomized clinical trials have consistently shown that CRT improves such functional endpoints as the 6-minute walk test (6MWT), NYHA class,
and quality-of-life (QOL) scores assessed with the Minnesota Living With Heart Failure Questionnaire (MLHFQ).10,11 Importantly, a recently reported large clinical trial has shown that CRT, when combined with evidence-based medical therapies, not only improves clinical symptoms, exercise tolerance, and the frequency of hospitalizations, but also reduces mortality.12
