Reduction in myocardial acidosis using blood cardioplegia

Abstract

The composition of the ideal cardioplegic solution is controversial. Blood cardioplegia is an attractive alternative to standard crystalloid solutions, though its superiority in preserving myocardial metabolism has not been demonstrated. Using a new pH electrode system, this study contrasts the effects of blood and crystalloid solutions upon the generation of myocardial acidosis during global ischemia. Thirty-eight mongrel dogs underwent a 120-min period of aortic cross clamping using systemic hypothermia. To maintain myocardial temperature below 15°C, 19 dogs received multiple doses of a bicarbonate containing crystalloid cardioplegic solution (Group I), while 19 dogs received multiple doses of blood cardioplegia (Group II). Myocardial pH and temperature were continuously monitored in the subendocardial region of the left ventricle. There was no difference in baseline pH between Group I (7.13 ± 0.05) and Group II (7.17 ± 0.05, P:NS). With systemic cooling and the initial bolus of cardioplegia, myocardial pH rose to 7.42 ± 0.04 in Group I and 7.42 ± 0.06 in Group II ( P:NS). After 120 min of global ischemia, myocardial pH decreased to 6.61 ± 0.05 in Group I and 7.07 ± 0.05 in Group II ( P < 0.001). Blood cardioplegia was most effective during the first hour of aortic cross clamp when myocardial pH rose by 0.13 ± 0.04 pH units. In contrast, myocardial pH in Group I during the first hour of global ischemia fell −0.35 ± 0.08 pH units ( P < 0.001 compared to Group II). During the second hour of cross clamp, myocardial pH declined both in Group I (0.26 ± 0.03 pH units) and in Group II (0.24 ± 0.05 pH units, P:NS). However, the accumulation of hydrogen ion during the second hour was significantly greater in Group I (+128.0 ± 21.4 nm/liter) than in Group II (+36.6 ± 9.0 nm/liter, P < 0.001). Thus, myocardial acidosis was reduced during the administration of blood cardioplegia when compared to a bicarbonate-buffered crystalloid solution. The salutary effects of blood cardioplegia on myocardial metabolism stem from blood's significant buffering capacity and its ability to deliver oxygen.