Effects of Varying Pacemaker Sites on Left Ventricular Performance

Abstract

The hemodynamic effects of the site of the artificial cardiac stimulation were studied in 17 open chest dogs. The right atrium and 5 ventricular sites (the inflow and outflow tracts and apex of the right ventricle, apex and lateral wall of the left ventricle) were stimulated electronically at a given rate, ranging from 130-190/min. When cardiac performance during ventricular pacing was compared with those during right atrial pacing, the former uniformly caused a diminution of cardiac output and systemic blood pressure, without reduction of left ventricular end-diastolic pressure. Ventricular function curves, in which left ventricular stroke work was related to left ventricular end-diastolic pressure, shifted downwards and to the right during ventricular pacing. Stimulation frequency did not alter these variables. The left ventricular dysfunction in ventricular pacing resulted from the absence of atrial contribution to ventricular filling, mitral regurgitation present and asynchronous ventricular contraction. No significant difference of cardiac performance was demonstrated by changing the site of ventricular pacing, suggesting that the mode of ventricular depolarization itself was not relevant to a decrease in cardiac performance.