Left ventricular volume reduction surgery for heart failure: A physiologic perspective

Background: Ventricular volume reduction surgery for idiopathic cardiomyopathy fails to improve cardiac output and is associated with a high incidence of recurrent heart failure. Volume reduction surgery achieved by removing akinetic or dyskinetic myocardium after myocardial infarction appears to be associated with better outcomes. The reasons for the differences in outcomes are not clear. Methods and Results: The hemodynamic effect of the major forms of volume reduction surgery were predicted by using a composite model of the left ventricle in which 20% of the myocardium was given properties of either weak but contracting muscle, an akinetic scar, or a dyskinetic scar (aneurysm). The end-systolic and end-diastolic pressure-volume relationships were determined numerically for each simulated operation. Any volume reduction procedure reduced chamber size, shifting end-systolic and end-diastolic pressure-volume relationships leftward. With resection of weak but contracting muscle, the leftward shift was greater for the end-diastolic than for the end-systolic pressure-volume relationship. Conversely, with resection of dyskinetic scar, the leftward shift was greater for end-systolic than for end-diastolic pressure-volume relationships. In contrast, resection of stiff scar shifted the 2 relationships equally. The effect on overall pump function was indexed by the relationship between total ventricular mechanical work and end-diastolic pressure. There was a beneficial effect on this relationship of resecting dyskinetic tissue, an equivocal effect of akinetic scar resection, and a negative effect of removing contracting myocardium. Conclusions: The effect of volume reduction surgery on overall ventricular pumping characteristics is determined by the differential effects on end-systolic and end-diastolic properties, which in turn are determined by the material properties of the region being removed.