[Phonomechanocardiographic analysis in patients with artifical pacemaker]

Eighteen patients with artificial pacemakers have been studied by phonomecanocardiographic means. All had complete atrio-ventricular block. Ten had an endocardial electrode in the right ventricle and 10 an epicardial in the free wall of the left ventricle. Two patients were studied, first with a temporal endocardial pacemaker and then with a permanent one. The studies were divided in 3 groups: Group I. In six cases comparison was made between the systolic tunes of the normally conducted cycles, and the ones produced by direct ventricular stimulations. The beats produced by direct ventricular stimulation showed a statistically significant diminution of the function of the left ventricle. This was reflected by a shorter relative ejection period. This diminution can possibly be explained by one of two mechanisms: absence of the "atrial kick", or alteration in the sequence of depolarization and ventricular contraction, producing an asynchrony in the contraction. This would lead us to suppose that the best site for contact of the electrode would be the middle third of the left aspect of the ventricular septum, where the activation starts normally. Group II. Ventricular function was compared in 20 cases, depending on the site of electrical stimulation: endocardium of right ventricle or epicardium of the left ventricle: there were no statistically significant differences. Group III. On 14 cases we studied cycles in which an effective contribution of the atrial kick could be expected, because the interval between the P wave and the electrical artifact was less than 300 msec. These were compared with others with a larger, statistically significant, improvement of the left ventricular function it was observed as a longer ejection period in the cases with a P wave-electrical artifact pause shorter than 300 msec.