ABSTRACT
INTRODUCTION Electrophysiological disturbances are common in the setting of chronic left ventricular dysfunction with or without heart failure. Approximately one-third of patients with systolic heart failure have a QRS duration greater than 120 msec, which is most commonly manifested as left bundle branch block (1,2). Such electrical disturbances result in left ventricular (i.e., intraventricular) dyssynchrony with paradoxical septal wall motion, which further impairs the pumping ability of an already struggling heart (3-6). In particular, left ventricular dyssynchrony causes suboptimal ventricular fi lling, a prolonged duration of mitral regurgitation, and a reduction in left ventricular dP/dt. Interventricular dyssynchrony also occurs in the setting of a bundle branch block, adversely affecting the timing of left and right ventricular ejection. Ventricular dyssynchrony, defi ned electrocardiographically by a prolonged QRS duration, has been associated with increased mortality in heart failure patients (7-10).
