Hemodynamic effects of atrial-ventricular sequential systole and physiological intra-ventricular contraction at various facing rates

The hemodynamic effects of atrial-ventricular sequential systole and physiological intraventricular contraction in normal conduction were evaluated by comparing left ventricular volume changes in atrial pacing (AP), A-V sequential pacing (AVP) and ventricular pacing (VP), using radioisotopic method. Eleven patients with sick sinus syndrome (SSS) received AP, 10 patients with SSS received AVP, and 8 patients with complete A-V block received VP. Three patients receiving AVP were studied again under VP. Using our new method, these patients were studied at pacing rates of 30 ppm to 130 ppm at ten ppm interval. Up to 70 ppm, left ventricular end-diastolic volume indices (LVEDVI) and stroke indices (SI) decreased slightly as pacing rate increased, while cardiac indices (CI) rose. No significant differences were noted between AP, AVP and VP. Over 70 ppm, LVEDVI and SI of AP and AVP decreased little, while CI increased more and more. However, LVEDVI and SI in VP decreased more than them in AP and AVP, while CI in VP increased little or decreased. Over 90 ppm, significant differences (p < 0.001) appeared between VP and the others. No significant differences were observed between AP and AVP. EF changed little between pacing rates. No significant differences were noted in EF between AP, AVP and VP. Conclusions were as follows: 1. Atrial-ventricular sequential systole was quite effective at pacing rates of over 70 ppm. 2. The presence or absence of physiological intra-ventricular contraction produced no significant hemodynamical difference. (author)