INTRODUCTION

Medical therapies, such as angiotensin converting enzyme inhibitors, beta blockers, and spironolactone, have led to marked improvements in both symptom control and overall survival in patients with heart failure (HF). (See "Overview of the therapy of heart failure due to systolic dysfunction".)

Implanted devices, such as cardioverter-defibrillators (ICDs) and pacemakers, can also be beneficial. ICDs are recommended for primary and secondary prevention of sudden cardiac death in selected patients with ischemic and nonischemic cardiomyopathy. (See "Secondary and primary prevention of sudden cardiac death in heart failure and cardiomyopathy", section on 'Primary prevention of SCD'.)

In addition, some patients with HF benefit from simultaneous pacing of both ventricles (biventricular or BiV pacing) or of one ventricle in patients with bundle branch block. This approach is referred to as cardiac resynchronization therapy (CRT) [1-6]. CRT can be achieved with a device designed only for pacing or can be incorporated into a combination device with an ICD (figure 1).

CRT is recommended in patients with HF (NYHA class II to IV), severe systolic dysfunction (eg, left ventricular ejection fraction (LVEF) ≤30 to 35 percent) and intraventricular conduction delay (eg, QRS ≥120 ms). The rationale for CRT is that ventricular dyssynchrony can further impair the pump function of a failing ventricle. Resynchronization may improve pump performance and reverse the deleterious process of ventricular remodeling. (See "Rationale for and mechanisms of benefit of cardiac resynchronization therapy".)

The clinical trials and indications for cardiac resynchronization therapy (CRT) in the management of patients with HF will be reviewed here. Implantation and other considerations for CRT therapy, studies evaluating standard dual-chamber pacing in HF and the possible role of CRT in patients with atrial fibrillation are discussed separately. (See "Cardiac resynchronization therapy in heart failure: Implantation and other considerations" and "Overview of cardiac pacing in heart failure" and "Cardiac resynchronization therapy in atrial fibrillation".)