Dynamic function of atrial contraction in regulation of cardiac performance

Abstract

Evidence has been obtained which demonstrates that atrial contraction consists of a peristaltic or wavelike contraction which propagates a pressure front toward the ventricle. When the pressure front reaches the ventricle, two events occur: 1) There is an atrial-induced rise in ventricular pressure along with an asynchrony in atrial and ventricular pressure which causes a negative difference in A-V pressure and closure of the A-V valve. 2) There is an atrial-induced rise in initial ventricular tension (end-diastolic pressure) and fiber length resulting in a marked augmentation of the ventricular response. By using the complete heart block preparation the atrial contribution to ventricular performance could be compared at an AS-VS interval in which it was maximum with an AS-VS interval in which there was no atrial contribution. The maximum increases in left ventricular performance were as follows: 12.2 cm H₂O in end-diastolic pressure; 40% in fiber length; 25 mm Hg in aortic pressure; 27 ml in stroke volume; and 33 g-m in stroke work.