Optimal timing for application of ventricular assist devices in patients who cannot be weaned from cardiopulmonary bypass. An experimental study.

Missing the moment for application of ventricular assist devices (VAD) may be one of the major causes of multiple organ failure in patients who are to be weaned from cardiopulmonary bypass (CPB) with the aid of VAD. To determine the optimal timing for application of VAD in such patients, we examined the effect of a CPB assist on cardiac functional recovery from severe global ischemia using an experimental canine system. In the present study we created myocardial ischemia by clamping the aorta for 20 minutes (Group I; N = 7) or 45 minutes (Group II; N = 11) under normothermic CPB. The reliability of the method in creating severe cardiac failure was confirmed by testing the levels of adenosine triphosphate (ATP), creatine phosphate (CP), and lactate. After reperfusion of the myocardium, the heart was assisted by a totally vented CPB. The left ventricular end-systolic pressure-volume relationship (Emax), which is a load-independent index of contractility, was obtained every 15 minutes for up to 120 minutes of reperfusion. The Emax revealed that the function of the damaged heart recovers exponentially with time after reperfusion. From curves of the functional recovery of the heart, CPB support appeared to be beneficial for the first 60 minutes after reperfusion, and aided in the recovery of cardiac function in hearts damaged by global myocardial ischemia. However, CPB assist thereafter may not be effective in further improving cardiac function. We therefore concluded that the decision to use VAD should be determined by cardiac function by 60 minutes of reperfusion to avoid prolonging CPB time.