Effect of pacemaker site on cardiac output and ventricular activation in dogs with complete heart block

Abstract

The sequence of ventricular activation was recorded in dogs with complete heart block while the heart was paced from each of 11 ventricular sites; cardiac output was determined while the heart was paced from each of 8 ventricular sites at rates of 90, 120 and 150 per minute. The following conclusions were reached: 1. 1. Each ventricular pacemaker site results in a specific pattern of ventricular activation. 2. 2. Differences of over 100 per cent in cardiac output were recorded when the heart was paced from different ventricular sites at the same pacemaker rate. 3. 3. The optimal pacemaker rate is dependent upon the ventricular site selected for the implantation of the pacemaker electrode and the condition of the cardiovascular system. 4. 4. The hemodynamic effectiveness of the left ventricular pacemaker sites is inversely related to the muscle mass activated by muscle conduction. 5. 5. The hemodynamic effectiveness of right ventricular pacemakers is dependent upon the pattern of left ventricular depolarization. 6. 6. The hemodynamically more effective left ventricular pacemaker sites resulted in higher cardiac outputs than any of the right ventricular sites tested. 7. 7. The changes in cardiac performance when the heart is paced from various pacemaker sites is best explained by varying degrees of asynchrony during ventricular contraction and/or the position of the atrioventricular valves early in ventricular systole. 8. 8. The clinical implications of this study have been considered.