What is cardiac resynchronization therapy?

Cardiac resynchronization refers to pacing techniques that change the degre e of atrial and ventricular electromechanical asynchrony in patients with m ajor atrial and ventricular conduction disorders. Atrial and ventricular re synchronization is usually accomplished by pacing from more than one site i n an electrical chamber-atrium or ventricle-and occasionally by stimulation at a single unconventional site. Resynchronization produces beneficial hem odynamic and antiarrhythmic effects by providing a more physiologic pattern of depolarization. Atrial resynchronization may prevent atrial fibrillatio n in selected patients with underlying bradycardia or interatrial block. It s antiarrhythmic effect in the absence of bradycardia is unclear. Ventricul ar resynchronization is of far greater clinical value than atrial resynchro nization. Biventricular (or single-chamber left ventricular) pacing is bene ficial for patients with congestive heart failure, severe left ventricular systolic dysfunction, dilated cardiomyopathy (either ischemic or idiopathic ), and a major left-sided intraventricular conduction disorder, such as lef t bundle branch block. The chan-c in electrical activation from resynchroni zation, which has no positive inotropic effect as such, is translated into mechanical improvement with a more coordinated left ventricular contraction . Several recent randomized trials and a number of observational studies ha ve demonstrated the long-term effectiveness of ventricular resynchronizatio n in the above group of patients. The high incidence of sudden death among these patients has encouraged ongoing clinical trials to evaluate the benef it of a system that combines biventricular pacing and cardioversion-defibri llation into a single implantable device. (C) 2001 by Excerpta Medica, Inc.