Intraoperative regional myocardial acidosis and reduction in long-term survival after cardiac surgery

Intraoperative myocardial pH_37C recorded from electrodes placed in anterior (solid line) and posterior (dotted line) walls of left ventricle of 65-year-old man undergoing aortic valve replacement. Time points at which cumulative myocardial pH_37C data were obtained for this study are illustrated on figure. Integrated mean pH_37C values during AC were 7.30 in anterior wall and 6.25 in posterior wall. In this study, lower of anterior and posterior pH_37C values in each patient defined degree of regional acidosis; in this patient it was posterior wall pH for each time point.

Survival probability curves (adjusted for other variables in the Cox proportional hazards regression model: age, preoperative ejection fraction, diabetes, year of surgery, operation type, surgeon, cardioplegia type, duration of AC, and duration of CPB) of patients in whom pH_37C was above (top line) or below (bottom line) threshold determined by automatic interaction detection analysis to affect most significantly long-term mortality. Risk ratio (RR) and 95% confidence interval (CI) of group with lower pH_37C versus group with higher pH_37C are shown on figure. Vertical line at 50% survival probability defines median survival for each patient group. A, Survivals of patients in whom lower of anterior or posterior wall pH_37C before AC was above (top) or below (bottom) 6.63. B, Survivals of patients in whom lower of anterior or posterior wall integrated mean pH_37C during AC was above (top) or below (bottom) 6.34 . C, Survivals of patients in whom lower of anterior or posterior wall pH_37C at discontinuation of CPB was above (top) or below (bottom) 6.34.

Survival probability curves (adjusted for other variables in Cox proportional hazards regression model: age, preoperative ejection fraction, diabetes, year of surgery, operation type, surgeon, cardioplegia type, duration of AC, and duration of CPB) for three groups of patients. First group (top tracing) had lower of anterior or posterior pH_37C before AC and at end of CPB above thresholds respectively determined to affect long-term survival. Second group (bottom tracing) had both values below such thresholds. Third group (middle tracing) had lower of anterior or posterior pH_37C before AC below threshold determined to affect long-term survival, and that at end of CPB above threshold. Risk ratio (RR) and 95% confidence interval (CI) of second and third groups versus first group are shown on figure. Vertical line at 50% survival probability defines median survival for each patient group.