COMPARISON OF RIGHT ATRIAL AND RIGHT VENTRICULAR SINGLE AND PAIRED PACING IN CANINE HEART

Sixteen mongrel dogs were previously prepared by destruction of the sinus node at right thoracotomy to obliterate significant atrial contraction and pacemakers were implanted to the right atrium and right ventricle. After surgical recovery, the dogs were anesthetized with pentobarbitone. Aortic pressure, left ventricular pressure plus its first derivative were measured. Cardiac output was sequentially determined using a Waters densitometer and Sanborn computer via a femoral artery sampling of indocyanine green injected into the right atrium. Stroke volume and work were calculated during single pacing of the right atrium and right ventricle and during paired pacing of the right ventricle, all at constant rates. The 3 types of pacing were measured at rest and during infusion of angiotensin to increase the afterload. Results show that single RA pacing is hemodynamically superior to single RV pacing in all instances as greater stroke volume and work is achieved, and the difference is due to loss of atrial contraction. During increased afterload within the limits of physiological compensation no further difference was found. Paired pacing of the right ventricle lowers the LVED pressure and increases dp dt of the left ventricular pulse but stroke work is the same as seen with RA pacing. The inotropic stimulus of paired pacing compensates for the acute loss of atrial contraction as seen with RVsp but even with increased afterload no further improvement is detected in the normal myocardium. © 1969.