Does secondary cardioplegia provide long-term recovery from ischemic injury?

Short-term experimental studies have indicated that initial reperfusion with blood cardioplegia may decrease ischemic injury after aortic occlusion; however, no long-term studies have been performed. We evaluated cardioplegic reperfusion in fifteen dogs, divided into three groups of five each. Group I underwent 2 hours of cardiopulmonary bypass at 37 degrees C. Group II underwent 2 hours of cardiopulmonary bypass, including 1 hour of ischemic arrest, at 25 degrees C. Group III was identical to Group II, but the hearts of the animals were initially reperfused with 500 ml of blood cardioplegia at 25 degrees C (K+ = 30 mEq/L). Stroke work index (SWI), left ventricular end-diastolic pressure (LVEDP), dp/dt max and maximal contractile element velocity (Vpm) were measured preoperatively, immediately after operation, 21 days postoperatively, immediately after operation, 21 days postoperatively and 120 days postoperatively. Compliance curves were evaluated using an intraventricular balloon at 120 days. Groups II and III had significant (p less than 0.05) elevations of LVEDP at all three postoperative measurements. The hearts of the Group III animals (cardioplegic reperfusion group) demonstrated significantly (p less than 0.05 to 0.01) better recovery of SWI immediately after operation (62% versus 39%), at 21 days (85% versus 69%), and at 120 days (81% versus 66%) than did those in Group II. However, groups II and III had decreased compliance at 120 days, compared with that of Group I, and also showed both gross and microscopic evidence of subendocardial necrosis and fibrosis. It is concluded that while initial reperfusion with blood cardioplegia appears to provide better preservation of ventricular function early after ischemic cardiac arrest, this technique does not prevent later deterioration of ventricular compliance. Moreover, it produces myocardial fibrosis.