Changes in passive but not active mechanical properties predict recovery of function of stunned myocardium

The time course of alterations in active and passive mechanical properties of stunned myocardium during ischemia and throughout reperfusion has not been thoroughly quantified. This investigation tested the hypothesis that the amount of injury as well as the rate and extent of recovery of contractile function in postischemic, reperfused myocardium are directly correlated to changes in regional active and passive elastance and viscosity. A modified viscoelastic Voigt model was employed to quantify myocardial mechanical properties. Left ventricular pressure and segment length (in both ischemic and normal regions) were fit to the model consisting of an active elastic spring in parallel with a viscous damper and a passive elastic spring. The mechanical properties of myocardium from dogs which recovered (> or = 50%) baseline regional contractile function as determined by percent segment shortening (n=7) were compared to those from dogs that did not recover function (n=7). Both groups displayed decreased active elastance in the ischemic region during coronary artery occlusion, and this decrease was maintained in the nonrecovery group. Increases in viscosity of ischemic myocardium were observed in both groups during coronary occlusion but returned to control only in the recovery group. The nonrecovery group demonstrated increased passive elastance in the ischemic region during coronary occlusion and throughout the reperfusion period whereas the recovery group remained unchanged. We conclude that functional recovery of stunned myocardium is directly related to alterations in mechanical properties caused by ischemia and that changes in passive elastance during occlusion may predict the ability of ischemic myocardium to recover contractile function.