Performance of pig heart after 30 or 120 minutes hypothermic arrest

The effect of the duration of hypothermic (T = 15°C) potassium cardioplegic arrest and ischemia on the heart was determined by measuring the response of the isolated in situ pig heart to 180 min of perfusion (n = 12) to provide appropriate control values for the study of 30 (n = 25) or 120 (n = 27) min of ischemia, followed by 60 min of reperfusion. In some of these animals, myocardial tissue samples were obtained for measurement of adenosine triphosphate (ATP) and creatine phosphate (CP), (6 in the perfusion group, 7 in the 30 min of ischemia and 60 min of reperfusion group and 15 in the 120 min of ischemia and 60 min of reperfusion group). In the remaining animals, measurements of either left ventricular performance (LVP), myocardial oxygen metabolism (MV?O₂) or plasma creatine kinase (CK) were obtained (6 in the prolonged perfusion group, 12 in the 120 min of ischemia and 60 min of reperfusion group, 6 LVP and MV?O₂ and 6 CK] and 18 in the 30 min of ischemia and 60 min of reperfusion group 13 LVP, 17 MV?O₂ and 6 CK]). During prolonged perfusion, left ventricular performance, expressed as developed pressure, ΔP, fell from an initial value of 175 ± 36 to 128 ± 19 mm Hg at 30 min of perfusion, followed by a more gradual decline to a final value of 113 ± 8 mm Hg at 180 min of perfusion. These decreases were not significantly lower than the initial value. The percentage of myocardial extraction declined in a similar manner, but coronary blood flow was constant over this interval. The primary effect of 30 or 120 min of ischemia was to reduce left ventricular developed pressure, ΔP, during reperfusion to more than 70% of the corresponding value in the control group (these differences were statistically significant) which suggests that prolonging the period of ischemia did not cause further deterioration of cardiac performance. The plasma concentration of CK rose in the control group of hearts subjected to prolonged perfusion from an initial value of 35 ± 6 to a final value of 59 ± 8 IU/liter (P < 0.05). While plasma CK increased during reperfusion in both ischemia/ reperfusion groups, these values were not significantly higher from prearrest values. Thus hypothermic cardioplegic ischemia of this duration did not appear to result in tissue necrosis, but there was a significant reduction in left ventricular performance which was independent of the duration of ischemia between the limits of 30 and 120 min.