Electromechanical Resynchronization with High Energy Septal Pacing

Abstract

Background: Standard cardiac pacing in the right ventricular apex alters electrical synchrony generating left bundle branch block that in some cases causes mechanical dyssynchrony. Pacing taking into account the anatomy (septal pacing) and with enough energy to narrow the QRS complex could have a beneficial effect, improving electrical and mechanical synchrony,and consequently myocardial function.Objective: The aim of this study was to evaluate acute electrical, mechanical and hemodynamic behavior in patients with severe intraventricular conduction disorders treated with high-energy septal pacing, and compare it with other pacing sites in the right ventricle (apex and outflow tract).Methods: Thirty patients whose average age was 65 years were continuously analyzed. They were divided into: Group I (n=15) with severe conduction disorders, complete left bundle branch block or complete right bundle branch block associated with left anterior hemiblock, all with dilated cardiomyopathy and ejection fraction (EF) <35%, and Group II (n=15) without conduction disorders and preserved EF.All patients underwent an electrophysiological study where the following parameters were evaluated in the acute phase: QRS duration in ms, time between the onset of surface QRS or spike and the most distal sites of the basal left ventricular (LV) wall, measured in the coronary sinus (R-LV), isovolumic contraction time (ICT) and ejection fraction measured by tissue Doppler echocardiography (performed off-line by an echocardiography specialist) and LV dP/dtmax assessed with an intracardiac Millar catheter (only in 18 cases). All these variables were evaluated at baseline (without pacing), with high energy septal pacing (7.5 V and 1 ms pulse width), and with right ventricular apical and outflow tract pacing. High energy pacing was used to evaluate the thresholds for QRS “narrowing”.Results: In Group I, QRS, R-LV and isovolumic contraction times improved with high energy septal pacing, but not with pacing in other sites, even with improved EF. Conversely, in Group II without conduction disorders, high energy septal pacing did not prolong QRS, R-LV or isovolumic contraction times, nor improved EF, but these parameters increased with pacing in other sites.Left ventricular dP/dtmax showed an average increase of 14% in 16 of the 18 patients evaluated in the acute phase.Conclusions: In patients with severe conduction disorders and low ejection fraction (EF), septal pacing allows electromechanical resynchronization with improved EF and dP/dtmax. In patients without conduction disturbances, this septal pacing does not modify electrical synchrony while pacing in other sites such as the right ventricular apex and outflow tract impairs it.