Normothermic blood cardioplegia reperfusion plus nifedipine after cardioplegic arrest: experimental study with a new delivery set

Abstract

During the aortic crossclamping and the early period of reperfusion, the calcium metabolism plays an important role in myocardial ischaemic damage. In this study, we test the use of a calcium entry blocker (nifedipine) during the early reperfusion period after cardioplegic arrest. The experimental protocol was tested on 20 large white pigs weighing 28 ± 1 kg. All animals underwent hypothermic (28°C) cardiopulmonary bypass (CPB) and St Thomas II cold (4°C) cardioplegia was infused in a single dose (40 ml/kg of body weight) through the aortic root after aortic crossclamping (90 minutes). The animals were divided into four groups (five animals for each group): Group I-standard reperfusion after clamping the aorta; Group II-the same as Group I plus nifedipine 100 mg bolus in aortic root just prior to unclamping the aorta; Group III-reperfusion was done with warm (37°C) oxygenated blood cardioplegia via aortic root (flow rate 70 ml/min/100 gm of heart weight, St Thomas I I solution with haematocrit of 1 5% for five minutes); Group IV-the same as Group III, plus nifedipine in bolus (100 nmg) injected in aortic root prior to the cardioplegic blood reperfusion. In Groups III and IV reperfusion was performed with a new delivery set (Dideco D51 5) which allows cold crystallaoid cardioplegia to be poured into warm blood cardioplegia. Full thickness myocardial biopsies were taken before, during (90') and after (3', 5', 10' of reperfusion) the aortic crossclamping and the level of high energy phosphate (H EP) of ATP, CP, lactate and myocardial water content were measured. Global left ventricular function was evaluated measuring left atrial pressure (LAP) at constant cardiac output with a right heart preparation before cardioplegic arrest and after 30 minutes of reperfusion. The results show significant differences during reperfusion between the four groups as follows: (a) higher ATP recovery in Groups III and IV than in Groups I and II; (b) CP levels increased more significantly in Group IV than in the other groups; (c) lactate was lower in Groups I I I and IV; (d) myocardial water content increased significantly in Group I; (e) global left ventricular function showed that the heart of the animals of Groups III and IV could pump from 3-3.5 I/min. with a left atrial pressure of less than 20 mmHg in respect to the other two groups. We conclude that after prolonged aortic crossclamping, the reperfusion with warm oxygenated cardioplegic blood plus nifedipine provides better myocardial protection.