Left ventricular volume reduction surgery for heart failure: A physiologicperspective

Background: Ventricular volume reduction surgery for idiopathic cardiomyopa thy 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 outcom es are not clear. Methods and Results: The hemodynamic effect of the major forms of volume re duction surgery were predicted by using a composite model of the left ventr icle 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 determin ed numerically for each simulated operation. Any volume reduction procedure reduced chamber size, shifting end-systolic and end-diastolic pressure-vol ume relationships leftward. With resection of weak but contracting muscle, the leftward shift was greater for the end-diastolic than for the end-systo lic pressure-volume relationship. Conversely, with resection of dyskinetic scar, the leftward shift was greater for end-systolic than for end-diastoli c pressure-volume relationships. In contrast, resection of stiff scar shift ed the 2 relationships equally. The effect on overall pump function was ind exed by the relationship between total ventricular mechanical work and end- diastolic pressure. There was a beneficial effect on this relationship of r esecting 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-sy stolic and end-diastolic properties, which in turn are determined by the ma terial properties of the region being removed.