Assessment of left ventricular function by a power index: an intraoperative study

Abstract

To investigate whether left ventricular performance can be described independent of loading conditions, twelve patients underwent intraoperatively two cineangiographies of the left ventricle with simultaneous pressure recordings. The first ventriculography was performed with ejecting left ventricle without assistance by the extracorporeal circulation. The second one was performed with ejecting left ventricle partially unloaded by the extracorporeal circulation. Myocardial perfusion pressure (mean aortic pressure) was held constant. Due to this procedure marked decreases in preload (end-diastolic wall stress: -54%) and modest changes in afterload (mean systolic wall stress: -23%) were achieved. End-diastolic volume index was reduced from 84 ml/m2 to 57 ml/m2, whereas end-systolic volume index decreased slightly from 33 ml/m2 to 29 ml/m2. Left ventricular end-diastolic pressure decreased from 12 mm Hg to 7 mm Hg, while peak pressure remained nearly unchanged. Usual parameters of ejection phase (EF, Vmw) as well as power per wall volume (PW) were markedly affected by unloading. In contrast to these parameters, the power index (PI), i.e., the ratio of power per wall volume and end-diastolic wall stress, remained unchanged when left ventricular preload was reduced: PI under control: 5.2 +/- 1.8 sec-1; PI under unloading: 5.2 +/- 1.5 sec-1. This power index can easily be determined from routine angiographies. It may provide a new approach to the assessment of left ventricular function in man.

Ventricular pressure-volume relations as the primary basis for evaluation of cardiac mechanics Return to Frank's diagram

“…The latter relation can easily be obtained, whereas determination of the area below the stress-velocity curve (which has the dimension of power) is more problematic (44). Relating the P-V area to the duration of systole should be restricted to the individual P-V loop (96), considering the fact that mechanical determinants influence the time-course of contraction. In addition, "contractility reserve" can be tested by inotropic interventions in animal experiments.…”

Evaluation of contractile state by maximal ventricular power divided by the square of end-diastolic volume.

“…Last, another study normalized mean power (versus PWRma) to estimated diastolic wall stress. 12 Incorporation of wall mass and geometry considerations via a stress formula may be useful for contrasting absolute values of power between subjects with markedly different heart sizes or thicknesses; however, this requires modeling assumptions. The present data were obtained in normal canine hearts with a fairly narrow range of cardiac masses, but in clinical disease states, particularly those with substantially increased chamber volume or mass, heart geometry could be important.…”

Ventricular systolic assessment in patients with dilated cardiomyopathy by preload-adjusted maximal power. Validation and noninvasive application.

“…In the 1970s, indexes based on PWRmX and maximal rate of change of PWRmX were proposed as improved methods to assess ventricular systolic performance. [23][24][25][26] However, these earlier studies did not or could not systematically evaluate loading influences on PWRmx or compare its inotropic response with independent meaningful standards. Furthermore, because PWRmx measurement required invasive data, it offered no particular advantage over other approaches.…”