The influence of left ventricular filling on postextrasystolic potentiation in the dog heart.

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Abstract
The role of left ventricular filling on postextrasystolic potentiation (PESP) was studied in the intact dog heart by calculating changes in end-systolic and end-diastolic volumes on a beat-to-beat basis from electromagnetic measurements of phasic mitral inflow and aortic outflow. In 13 dogs 161 extrasystolic sequences with compensatory pauses were analyzed. The 1st postextrasystolic cycle showed an increased end-diastolic volume (EDV) in 94%, a decreased end-systolic volume (ESV) in 50% and an estimated increased ejection fraction in 85% of the sequences. In 91 sequences with a coupling index .ltoreq. 0.7, despite a 76% increase in filling time, there was during the compensatory pause only a 6% increase in filling volume when compared to control. The net filling volume, stroke volume and diastolic filling period for the sum of the extra- and postextrasystolic cycles were, respectively, 78%, 80% and 116% of the sum of 2 control cycles. The retarded filling rate is due to a lower left atrial pressure, a reduced left ventricular relaxation rate and a relaxation to a higher pressure minimum; all decrease the amplitude of the atrioventricular pressure gradient. In 98% of the postextrasystolic cycles stroke volume was augmented when compared to control (ratio, 1.49 .+-. 0.26; mean .+-. SD), due in part to intrinsic mechanisms, to increased preload (EDV) and to decreased afterload. As a 1st approximation, the effects of increases in preload were separated from intrinsic increases in contractility after an extrasystole by defining potentiation in terms of decreased ESV and/or increased ejection fraction. With the former criterion, 50% of the sequences showed PESP; with the latter, PESP occurred in 85% of the sequences.