Intramural Dyssynchrony from Acute Right Ventricular Apical Pacing in Human Subjects with Normal Left Ventricular Function

Ventricular pacing causes early myocardial shortening at the pacing site and pre-stretch at the opposing ventricular wall. This contraction pattern is energetically inefficient and may lead to decreased cardiac function. This study was designed to describe the acute effects of right ventricular apical (RVa) pacing on dyssynchrony and systolic function in human subjects with normal left ventricular (LV) function and compare these effects to pacing from alternate ventricular sites. Patients (n=26) undergoing an electrophysiology evaluation were studied during atrial pacing (AAI) and dual chamber pacing from the RVa, left ventricular free wall (LVfw), and the combination of RVa and LVfw (BiV). Tissue Doppler imaging was used to measure intramural dyssynchrony by utilizing an integrated cross-correlation synchrony index (CCSI) from the apical 4-chamber view. RVa and BiV pacing significantly reduced systolic function as measured by longitudinal systolic contraction amplitude (SCA(long)) (p<0.05) and LV velocity time integral (VTI) (p<0.05) compared to AAI and LVfw pacing. RVa (and to a lesser extent BiV) pacing resulted in septal and lateral intramural dyssynchrony as indicated by significantly (p<0.05) lower CCSI values as compared to AAI. CCSI was significantly (p<0.05) worse during RVa than LVfw pacing. In patients with normal LV function, acute ventricular pacing in the RVa alone, or in conjunction with LVfw pacing (BiV), results in impaired regional and global LV systolic function and intramural dyssynchrony as compared to LVfw pacing alone.