Cardiac Resynchronization for Heart Failure: Present Status

Ventricular dysfunction is a hallmark of heart failure, and is often linked to ventricular dilatation and ventricular conduction delays. Recent studies have demonstrated that systolic function can be improved in patients with left bundle branch block by pre-exciting the site of late activation, usually the left ventricular free wall. Furthermore, it has been recently reported that this improvement is associated with a decrease in myocardial oxygen consumption. We hypothesize that the pre-excitation of the region covered by the blocked bundle acts as an "electrical bypass," resynchronizing the contraction of the septum and the left ventricular free wall. In addition, optimization of the electronic atrioventricular delay allows the simultaneous resynchronization of the atrioventricular contractions, and minimization of diastolic mitral regurgitation. Systolic mitral regurgitation may also be reduced by removing the geometric distortion introduced by the left bundle branch block. The recently reported positive outcome of the PATH-CHF I controlled trial reinforces that the positive acute and chronic results that have been reported up to now may translate into long-term clinical benefit for patients with heart failure and conduction defects. Larger studies are needed to confirm these initial results and to establish the impact of this new therapeutic modality on morbidity and mortality.