The Biochemical Study on Myocardial Protection during Cardiopulmonary Bypass

Abstract

The technique of a selective continuous coronary perfusion with cold oxygenated blood of low flow rate for protecting the ischemic myocardium under the aortic cross-clamping dur ing open-heart surgery had been applied in our department since November,1973. The effe ct of this technique was searched experimentally and clinically in this study.
Experimentally, the effect of 2-hour period of the selective continuous coronary perfusion with cold blood during the aortic cross-clamping was compared with those of the selective continu ous coronary perfusion with cold Ringer-lactate solution and of the topical cooling with cold physiological saline solution, using normal adult dogs as well as dogs with experimentally produced left ventricular hypertrophy. Twenty adult mongrel dogs, weighing 12 to 15 kilograms, and 10mongrel dogs with left ventricular hypertrophy produced by banding of the ascending aort a were subjected to total body perfusion.
In the group of cold blood coronary perfusion, oxygen amount extracted from myocardium was 0.006 to 0.01ml/min/gm of myocardial weight even at 15°C of myocardial tempe rature and an anaerobic metabolism was not demonstrated during the myocardial hypothermia, which indicated that the metabolic process contnued 15°C of the myocardial temperature. After release of the aortic cross-clamping or after weaning from the cardiopulmonary byass, the myocardial metabolism and the cardiac function were satisfactorily maintained. These findings we re essentially similar to those in the group with left ventricular hypertrophy of cold blood coronary perfusion. Moreover, the findings at 2-hour period of the aortic cross-clamping and at the period after release of it and after weaning from the cardiopulmorary bypass in the group of cold Ringerlactate coronary perfusion without oxygenated blood were almost same as those in the g roup of cold blood coronary perfusion, so far as myocardial temperature was maintained below 15°C.
On the contrary, in the group of topical cooling, an anaerobic metabolism remained during the period after release of the aortic cross-clamping and also after weaning from the cardiopu lmonary bypass. Moreover, in this group, the rate of weaning from the cardiopulmonary bypass was significantly lower than those in both groups of coronary perfusion, although as to the cardiac functions after weaning from the bypass, they differed little. The degree and the duration of anaerobic metabolism in the myocardium after release of the aortic cross-clamping in the group with hypertrophied left ventricle of topical cooling were more severe than those in the group with non-hypertrophied heart of topical cooling. These results showed that topical cooling could not provide a protection for ischemic myocardium in both normal dogs and dogs with left ventricular hypertrophy.
Clinically,25 patien ts with significant myocardial hypertrophy (15 patients with right ventricular hypertrophy and 10, with left or both ventricular hypertrophy) were selected from patientsgroups who underwent the technique of cold blood coronary perfusion from November,1973 to December,1977, in whom the duration of the aortic cross-clamping during open-heart surgery was over 60 minutes (60 to 214 minutes, average 94 minutes). In this series, the myocardial metabolism during and after cold blood coronary perfusion was examined. Furthermore, a serial creatine phosphokinase MB isoenzyme (CPK-MB) activity after weaning from the extracorporeal circulation was measured in other 13 patients who underwent cold blood coronary perfusion and was compared with the data of another group of patients who did not undergo this technique. At 15°C of myocardial temperature,2.5 to 3.0ml/min of oxygen were extracted from the myocardium during hypothermic coronary perfusion. The myocardial metabolism during cold blood coronary perfusion or during rewarming period after release of the aortic cross-clamping were satisfactorily