Interstitial pH value in the myocardium as indicator of ischemic stress of cardioplegically arrested hearts.

The influence of different cardioplegic methods (Bretschneider, Cardiac Surgery in Hamburg, Kirklin, St. Thomas' Hospital in London) on the progressive myocardial acidosis during global ischemia of up to 24 hours' duration was investigated in arrested, nonperfused canine hearts (n = 36). The increasing acidosis of the ischemic heart muscle was continuously measured and registered with the aid of interstitial pH measurement (pHi) using glass implant electrodes. With various buffered and unbuffered cardioplegic solutions there were relatively wide fluctuations of the pHi courses in the myocardial extracellular space. The "critical" interstitial pH values ("pHcrit") relative to a defined myocardial ATP concentration (4 mumol/g ww) vary between 6.10 (Bretschneider) and 5.6 (Kirklin) (p less than 0.001). These striking results cannot be attributed solely to different total myocardial lactate concentrations, but variations in a "cellular" and an "extracellular factor" must also be taken into account. Measurement of interstitial pH for intraoperative monitoring of myocardial ischemic stress can therefore be used only within limits and with knowledge of the specific protective procedure applied. The method continues an important tool in basic investigations of partial or global ischemia of organs, particularly as regards the spectrum of metabolic, morphological and functional parameters.