The variable functional effects of the pacing site in normal and scarred ventricles

BACKGROUND The pacing site has been shown to influence functional improvement with cardiac resynchronization therapy. We evaluated the effects of the pacing site on left ventricular (LV) function in an animal model. METHODS AND RESULTS Equilibrium radionuclide angiography was acquired in sinus rhythm (NSR) and with ventricular pacing, from three pacing sites in seven normal and eight infarcted dogs. QRS duration, electrical activation pattern, wall motion, LV ejection fraction (EF), synchrony of ventricular contraction, and mean arterial pressure (MAP), were related to the pacing site and infarct size, during each of 120 episodes. Little changed during pacing in normals. In infarcted dogs, LV wall motion, and synchrony worsened, LVEF and MAP often fell. These changes related to altered activation patterns which were influenced by the pacing site but were not related to infarct size. CONCLUSIONS Hemodynamic and functional LV changes after infarction were found to vary with the pacing site and associated conduction and synchrony.