Warm and cold blood cardioplegia. Comparison of myocardial function and metabolism using 31p magnetic resonance spectroscopy

Abstract

Background: Standard myocardial protection during cardiac surgery uses hypothermic arrest, but warm heart surgery, recently introduced, is now used in many centers. We hypothesized that warm continuous blood cardioplegia (WCBC) would provide better myocardial preservation than cold continuous blood cardioplegia (CCBC).

Methods and results: In isolated cross-perfused canine hearts, left ventricular (LV) function and myocardial O2 consumption (MVO2) were measured at constant LV volume, coronary perfusion pressure, and heart rate before and after 75 minutes of arrest at 37 degrees C or 10 degrees C. Metabolism was evaluated by 31P nuclear magnetic resonance spectroscopy. LV resting tone increased transiently after arrest by CCBC but not WCBC (38 +/- 3.9 versus 2.9 +/- 0.5 mm Hg, P < .0005). Myocardial ATP changed over time differently in the groups (P < .001), declining at the outset of CCBC and returning to control levels during the recovery period after CCBC or WCBC. Intracellular pH rose from 7.17 +/- 0.03 to 7.85 +/- 0.05 during CCBC (P < .0005 versus WCBC). MVO2 declined dramatically during arrest at either temperature but to a lower value during CCBC (P < .0005). LV pressure recovered to 86.1 +/- 5.1% of its prearrest value after CCBC and to 97.2 +/- 7.8% following WCBC (P = NS). After CCBC but not WCBC, there were small but significant increases in LV end-diastolic pressure (by 1.3 mm Hg, P < .05) and in the LV relaxation constant, tau (from 37.3 +/- 1.5 to 42.3 +/- 2.4 milliseconds, P < .05).

Conclusions: The increase in intracellular pH during CCBC is largely accounted for by physicochemical factors. Group differences in ATP over time may be related to rapid cooling contracture during CCBC. The data suggest that CCBC mildly impairs LV function but that WCBC preserves function and metabolism at or near prearrest levels.