Cardiac Resynchronization Therapy for Heart Failure

Abstract

He weight of evidence supporting the routine use of cardiac resynchronization therapy, or atrial-synchronized biventricular pacing, as a treatment for patients with moderate-to-severe chronic systolic heart failure and ventric- ular dyssynchrony is now quite substantial. Results from mechanistic studies, observational evaluations, and random- ized, controlled trials have consistently demonstrated signif- icant improvement in quality of life, functional status, and exercise capacity in patients with New York Heart Associa- tion (NYHA) class III and IV heart failure who are assigned to active resynchronization therapy. 1-3 In these patients, cardiac resynchronization has also been shown to improve cardiac structure and function while significantly reducing the risk of worsening heart failure. 1,2 In 2001, the first resynchronization device became commercially available in the United States. The following year, 2 devices that combine biventricular pacing capability with implantable cardioverter defibrillators (ICDs) were approved for use by the US Food and Drug Administration. Recently updated ACC/AHA/ NASPE Pacemaker and ICD Guidelines included cardiac resynchronization therapy as a class IIA recommendation for pacing.4 Since that time, preliminary results from another large-scale trial have suggested a significant reduction in the combined end point of all-cause mortality and all-cause hospitalization with cardiac resynchronization therapy in an advanced heart failure population.5 The present article briefly reviews the rationale for and mechanisms of cardiac resyn- chronization therapy in heart failure as background to a more in-depth discussion of landmark clinical trials. Patient selec- tion and limitations/pitfalls of resynchronization therapy are also discussed. Rationale for Cardiac Resynchronization Therapy Approximately one third of patients with systolic heart failure have a QRS duration greater than 120 ms, which is most commonly seen as left bundle-branch block (LBBB).6,7 In LBBB, the left ventricle is activated belatedly through the septum from the right ventricle, resulting in a significant delay between the onset of left ventricular (LV) and right ventricular contraction. 8,9 Activation of the anterior septum