Effect of site of synchronous unipolar ventricular stimulation and volume loading on cardiac function

Abstract

Multilead atrioventricular synchronous unipolar pacemakers were implanted in dogs with complete heart block. After recovery from pentobarbital anesthesia, ventricular stimulation site was varied by magnetically opening and closing lead switches through the intact skin of the resting dog. Electrocardiogram, cardiac output, and central arterial and venous pressures were monitored for 16–72 hr. Each stimulation site gave a characteristic ECG but pulse rate was not affected. When compared with the other sites studied, left ventricular apical stimulation increased cardiac output ( P < 0.001) and systemic pressure ( P = 0.01) and decreased central venous pressure ( P < 0.05). While less effective than the left ventricle apex, stimulation of either the base or the apex of the right ventricle gave better cardiac output than stimulation of the base of the left ventricle ( P < 0.01 and < 0.05). After volume loading cardiac output increased. Left ventricular apical stimulation remained optimal and the significance of the pressure changes increased ( P < 0.001). For maximum cardiac performance after complete heart block, pacemaker electrodes should be implanted at the left ventricular apex. Lead implantation at the left ventricular base is practiced to decrease lead stress but should be avoided as this site consistently limits cardiac function.