Optimization of cardiac resynchronization therapy: technical aspects

Biventricular pacing results in significant haemodynamic improvements in most patients with chronic heart failure and intra-ventricular conduction delay, especially those with left bundle branch block. A growing body of experience indicates that the pacing site and the choice of atrioventricular/intraventricular delay are crucial to short-term improvement in left ventricular (LV) function. In patients with left bundle branch block, the mid-lateral and mid-postero-lateral wall of the left ventricle have been identified as the regions at which the latest activation occurs. Thus, they present the most effective pacing sites on the left ventricle. The importance of an appropriately timed atrial contraction for ventricular loading is well established, because prolongation of the atrioventricular interval (common in patients with chronic heart failure) provokes a reduction in the LV active filling phase, a shortening in passive diastolic filling and onset of a ventriculo-atrial gradient, thus initiating diastolic mitral regurgitation. Atrioventricular delay optimization can limit these deleterious haemodynamic effects, although the influence of atrioventricular delay appears to be less important than proper choice of LV pacing site. The latest generation of biventricular pacing devices are equipped with two separate channels for the right ventricular and LV leads, thus allowing the interventricular timing of pacing to be varied, obtaining haemodynamic benefits even from a non-optimal LV site.