MYOCARDIAL OXYGENATION AND TRANSMURAL LACTATE METABOLISM DURING EXPERIMENTAL ACUTE CORONARY STENOSIS IN PIGS

Measurement of surface tissue pO2(ptO2) with surface electrodes is increasingly applied in experimental medicine. Its use on the beating heart may seem to be problematic because transmural gradients of tissue pO2 would reduce the validity of pO2 determinations in the epicardial layers. This study attempted to determine whether ptO2 may be a valid and sensitive indicator of transmural myocardial oxygenation. In order to measure ptO2, two eight-channel Clark-type electrodes were placed on a beating porcine left ventricle (n = 13). Measurements were made at different degrees of acute stenosis of the left anterior descending artery (LAD). A 24-F cannula was inserted into the great cardiac vein, draining the poststenotic myocardium to obtain coronary venous blood samples. Transmural metabolic changes were detected simultaneously by coronary venous blood gas parameters and lactate levels. Epicardial tissue pO2 was 49 +/- 2 mm Hg (mean +/- SEM) before stenosis and decreased to a mean value of 25 +/- 2 mm Hg during stenosis. Different degrees of LAD stenosis (ptO2 range: 12-35 mm Hg) were substantial enough to alter arterio-coronary venous lactate difference (avd lactate) from +0.31 +/- 0.07 mmol/l (control) to -0.62 +/- 0.15 mmol/l (stenosis). A significant linear correlation between changes of ptO2 (DELTA-ptO2) and changes of avd lactate (DELTA-avd lactate) resulted (y = 0.59 + 0.62x; r = 0.86; p less-than-or-equal-to 0.001). However, linear regression analysis between DELTA-ptO2 correlated with the corresponding data from coronary venous pO2 (DELTA-pO2cv) oxygen content (DELTA-O2cont(cv), and oxygen saturation (DELTA-O2sat(cv)) showed no significant correlations. We conclude that measurement of ptO2 is a sensitive and valuable indicator of transmural oxygenation in ischemic myocardium, whereas pO2(cv), O2cont(cv) and O2sat(cv) do not seem to be valid predictors of ischemia in myocardial oxygenation.