Ischemic tolerance of the arrested heart during warm cardioplegia

Normothermic blood cardioplegia has recently generated interest as an alternative method of myocardial protection during cardiopulmonary bypass (CPB) surgery. One disadvantage is the obligatory interruption of coronary flow during the distal coronary anastomosis. This study was designed to determine the safe normothermic ischemic time of the arrested and decompressed heart. Under normothermic CPB (37 degrees C), initial cardioplegic arrest was induced with 750 cc of warm (37 degrees C) hyperkalemic blood cardioplegia in 21 adult dogs. The heart then received warm blood cardioplegia either continuously (50 cc/min), every 5 min (250 cc each) or every 10 min (350 cc each) for a total equivalent ischemic time of 30 min (n = 7 in each group). Left ventricular pressure-volume (PV) loops were measured by micromanometer and conductance (volume) catheters before, at 60 and 90 min after aortic cross-clamping. Systolic function was measured as the preload recruitable stroke work area derived from the stroke work-end diastolic volume relationship, and the diastolic stiffness constant (k) was derived from the exponential diastolic PV relationship. The q5 min group sustained minor deterioration in diastolic function while its systolic function was well maintained during recovery. There were significant reductions in both the diastolic and systolic functions in the q10 min group. The maximum drops in the septal wall pH during aortic cross-clamping were 0.05 +/- 0.02 (not significant), 0.19 +/- 0.06 (P0.05), and 0.40 +/- 0.09 (P0.01) for the continuous, q5 min and q10 min groups, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)