Effects of regional ischemia and ventricular pacing on LV dP/dtmax-end-diastolic volume relation.

We investigated the effects of coronary artery occlusion and pacing from ventricular sites on the relation of the maximum rate of rise of left ventricular pressure (dP/dtmax) to the end-diastolic volume (VED) in dogs previously instrumented to measure left ventricular pressure and to determine left ventricular volume from three ultrasonically measured dimensions. The dP/dtmax-VED relation was generated by vena caval occlusion and compared with the simultaneously produced end-systolic pressure-end-systolic volume (PES-VES) relation. The dP/dtmax-VED relation was described by a straight line during all conditions. Occlusion of the left circumflex coronary artery produced a rightward shift of the dP/dtmax-VED relation, increasing the volume intercept by 11.3 +/- 5.3 (SD) ml (P less than 0.05). Compared with atrial pacing, the dP/dtmax-VED relation was shifted to the right with the volume intercept increasing by 4.8 +/- 4.4 ml (P less than 0.05) during pacing from the right ventricular free wall, 3.7 +/- 5.0 ml (P less than 0.05) during pacing from the right ventricular apex, and 3.7 +/- 2.4 ml (P less than 0.05) during pacing from the left ventricular free wall. Similar increases were observed in the volume intercepts of the PES-VES relations during coronary occlusion or ventricular pacing. These results are consistent with the predictions of the time-varying elastance model and support its use as a conceptual framework to understand left ventricular performance during isovolumic contraction and at end systole, both in the normal ventricle and the ventricle with regional abnormalities of contraction.