Ischemic Preconditioning, Cardioplegia or Both?

With the continuing search for superior methods of myocardial protection, we compared the protective efficacy of ischemic preconditioning with that of St Thomasʹ cardioplegia, alone and in combination, against vascular and myocyte injury during ischemia and reperfusion. Rat hearts were perfused with blood for 20 min, subjected to zero flow global ischemia for 35 min (37°C) and reperfused for 40 min. Left ventricular developed pressure (LVDP) was assessed with an intraventricular balloon. Coronary flow was measured at a constant perfusion pressure. Study groups (n=8 hearts/groups) were: (i) controls (unprotected ischemia), (ii) preconditioning (PC, 3 min ischemia + 3 min reperfusion), (iii) cardioplegia (CP, infused for 1 min before ischemia) and (iv) PC+CP. The post-ischemia recoveries of LVDP were 26±6, 44±2, 53±3 and 54±4% respectively (P<0.05 all others v control). Post-ischemic coronary vascular resistance increased in controls by 167±60% from its pre-ischemic baseline value but was well protected with PC, CP and PC+CP (changing by only + 11±7, + 27±10 and —2±6% respectively). Conclusions: Preconditioning and cardioplegia alone afford similar and substantial protection of post-ischemic contractile and vascular function. The combination of the two affords no significant additional protection.