Abstract
The continuous measurement of intramyocardial pH was used to follow the progression of ischemia and permit correlation to functional recovery. Adequacy of myocardial preservation following 38°C or 25°C global ischemia alone or with the administration of one or two doses of 38°C, 25°C, or 1°C crystalloid cardioplegia at aortic root perfusion pressures of 90 mm Hg or 130 mm Hg was assessed. A new miniature myocardial transducer incorporating fiberoptic technology and dual pH and temperature-sensing capability was placed into the left ventricular free wall and septum of 44 sheep undergoing ischemic arrest during cardiopulmonary bypass. All groups underwent global ischemia until myocardial pH was 6.8. An intramyocardial pH level of 6.8 reliably correlated to similar levels of functional recovery in each group. Aortic root perfusion pressure of 130 mm Hg provided enhanced myocardial protection by increasing the total ischemic time (5 to 10 minutes) with one ( p < 0.01) or two ( p < 0.001) doses of cardioplegic solution until a given functional level of recovery was attained. Aortic root perfusion pressure of 90 mm Hg provided no added benefit in total ischemic time, rate of change of pH, or degree of recovery of function. Hypothermic (25°C) global ischemia alone enhanced myocardial protection by providing increased time ( p < 0.01) until a given functional level of recovery was attained with a slower rate of change of pH ( p < 0.01) compared with normothermic (38°C) global ischemia alone. Very cold (1°C) cardioplegia during hypothermic (25°C) global ischemia greatly enhanced myocardial protection by providing increased time (92 minutes) until a myocardial pH value of 6.8 was attained. It is concluded that continuous measurement of interstitial myocardial pH and temperature is a practical and useful method for assessment of the adequacy of myocardial protective methods and solutions.
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