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Ann Thorac Surg 1986;42:31-36
© 1986 The Society of Thoracic Surgeons

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Articles

Continuous Measurement of Intramyocardial pH: Correlation to Functional Recovery Following Normothermic and Hypothermic Global Ischemia

From the Surgery Branch, National Heart, Lung, and Blood Institute, Bethesda, MD

Accepted for publication October 9, 1985.

^* Address reprint requests to Dr. Takach, Surgery Branch, NHLBI, Bldg 10, Room 2N242, Bethesda, MD 20892

The continuous measurement of intramyocardial pH was used to follow the progression of ischemia and was correlated to the recovery of left ventricular function following normothermic (38°C) and hypothermic (25°C) global ischemia. New miniature myocardial transducers, which incorporate fiberoptic technology and dual pH- and temperature-sensing capability, were placed into the left ventricular free wall and septum of 52 sheep undergoing cardiopulmonary bypass. Left ventricular stroke work as a function of mean left atrial pressure curves were generated before and after cardiopulmonary bypass by volume loading with whole blood. Functional recovery was determined by the ratio of the integrals of the preischemic and postischemic function curves. Control sheep (N = 11) did not undergo ischemia. Three groups (N = 41) underwent aortic cross-clamping until pH reached 7.0, 6.8, or 6.6. The preischemic myocardial pH averaged 7.42 ± 0.01. Following both normothermic and hypothermic global ischemia, no significant difference was demonstrated in recovery of function between control (pH 7.4) and pH 7.0 groups at either temperature. However, recovery of function of the pH 6.8 and pH 6.6 groups was significantly decreased (p < 0.01) versus control and pH 7.0 groups at both temperatures. No significant difference in recovery of function was demonstrated at any pH level when normothermic versus hypothermic groups were compared. However, hypothermia provided increased time (p < 0.001) before each level of function was reached with a slower rate of change of pH (p < 0.01) compared with the corresponding same pH group in sheep undergoing normothermic (38°C) cardiopulmonary bypass. An interstitial myocardial pH lower than 7.0 at the termination of ischemia resulted in a marked decrease in left ventricular function following both normothermic and hypothermic global ischemia and reperfusion. The terminal ischemic pH value correlated to similar left ventricular functional levels of recovery at 38°C and 25°C, and rate of change of myocardial pH predicted the interval of ischemia required to achieve a given functional level of recovery.

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