Cardioplegia and vascular injury: Dissociation of the effects of ischemia from those of the cardioplegic solution

Abstract Although cardioplegic solutions successfully protect myocardial contractile cells against ischemic injury, their effect on the vasculature remains controversial. To address this we used a vascular bed preparation (isolated rat mesentery) that permits the study of vascular function without the coincident changes in contractile status that affect vascular tone (and hence the assessment of vascular function in isolated hearts). Smooth muscle cell contraction was assessed by measurement of the vasoconstrictor response to phenylephrine, and relaxation was assessed by measurement of the vasodilator responses to sodium nitroprusside and the endothelium-dependent relaxant adenosine triphosphate. After characterization of basal vascular function, mesenteries were subjected to normothermic ischemia for 60, 90, 120, 150, and 180 minutes ( n = 12 for each time period; 6 preparations were subjected to ischemia alone and 6 to ischemia preceded by a 3-minute infusion of the St. Thomas' Hospital cardioplegic solution). The tissue was then reperfused for 20 minutes and vascular function reassessed. Ischemia alone caused progressive time-dependent deterioration in vasoconstrictor responses (99% ± 13%, 90% ± 10%, 63% ± 6%, 51% ± 10%, and 27% ± 4%), endothelium-independent vasodilation (93% ± 3%, 86% ± 2%, 78% ± 5%, 61% ± 5%, and 38% ± 9%), and endothelium-dependent vasodilation (93% ± 3%, 96% ± 2%, 94% ± 2%, 87% ± 7%, and 62% ± 11%). There were similar time-dependent deteriorations in mesenteries subjected to ischemia coupled with cardioplegic solution that were not significantly different from any of the ischemia-alone groups when matched for ischemic times. Thus, for example, after 180 minutes of ischemia alone, the vasoconstrictor response was 18% ± 3%, endothelium-independent vasodilation was 44% ± 7%, and endothelium-dependent vasodilation was 40% ± 9%. The results demonstrate that under the conditions of this experiment, the St. Thomas' Hospital cardioplegic solution neither protects nor injures the vasculature during an episode of ischemia and reperfusion. However, in studies with 150 minutes of normothermic ischemia, multiple infusions of cardioplegic solution (given every 30 minutes during ischemia) resulted in protection of smooth muscle and endothelial function. Thus, after multiple infusions, vasoconstriction to phenylephrine was 74% ± 4%, vasodilation to nitroprusside was 81% ± 6%, and vasodilation to adenosine triphosphate was 89% ± 5%. In conclusion, when the St. Thomas' Hospital cardioplegic solution is used as a single infusion and coupled with ischemia, the solution fails to protect smooth muscle and endothelial function against ischemic injury, but some protection is obtained when the solution is infused intermittently throughout the ischemic period. (J T HORAC C ARDIOVASC S URG 1994;108:279-90)