Abstract
Comparative mitochondrial ultrastructural changes during myocardial ischaemic periods have been assessed when using four different solutions: Bretschneider's solution (BS) (K+ = 10 mEq/l) at 4°C; St Thomas's hospital solution (STS) (K+ = 20 mEq/l) at 4°C; standard Ringer's solution (SRS) (K+ = 2.7 mEq/l) at 4°C; blood potassium cardioplegic solution (BPS) (K+ = 21 mEq/l) at 15°C.
BS (n = 8), STS (n = 10), SRS (n = 8) and BPS (n = 8) were infused in 34 patients undergoing aortic valve replacement (n = 17) or aortocoronary bypass grafting (n = 17), after aortic crossclamping, either in the aorta or in both coronary ostia, until the septal myocardial temperature reached 10-13°C for crystalloid solutions or 15°C for blood cardioplegia. Myocardial biopsies were taken from the left ventricular apex, on a beating heart, at the beginning and end of bypass.
To assess the degree of ischaemic injury, an ultrastructural evaluation of the mitochondria was done and four histological classes have been defined: class I- dense matrix and cristae; class II — occasional mitochondrial swelling; class III — decrease in matrix density with extensive swelling; class IV — severe swelling and/or rupture of matrix.
This study showed that: (1) only the St Thomas's and Bretschneider's solutions provide a rapid electromechanical asystole; (2) isolated hypothermic crystalloid solution with low potassium concentration (standard Ringer) is not sufficient either to induce cardiac arrest or to prevent detrimental mitochondrial changes; (3) Bretschneider's solution appears to provide the best ultrastructural mitochondrial preservation during myocardial ischaemia.
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