Comparison of myocardial preservation techniques for aortocoronary bypass surgery

Abstract

The myocardial properties of three different techniques for cardiac arrest during aortocoronary bypass surgery were analyzed. Ventricular fibrillation and moderate total body hypothermia (30–33°C) (Group I) was found to be an insecure method of preservation. It produced a high incidence of focal irreversible ultrastructural changes (7 of 10 patients), high post-bypass CK-MB levels (mean 85.54 U/liter) indicative of myocardial damage, and impaired clinical and physiologic recovery courses. Six out of ten patients needed inotropic support, three had prolonged stay in ICU, and three patients showed Type III (unacceptable) recovery trajectories, one of whom died of myocardial decompensation four weeks after surgery. This method, which was the most common one used in our institution, was completely abandoned as a result of these studies. Potassium induced cardioplegia combined with methylprednisolone sodium succinate, hypertonic glucose and intermittent moderate topical cooling (25–27°C) of the heart (Group III) offered a generally acceptable form of myocardial protection, as only one patient showed irreversible ultrastructural changes. The mean post-bypass CK-MB level was only moderately elevated (mean 22.32 U/liter), but seven of ten patients needed inotropic support. There were no Type III recovery trajectories and two patients showed an optimal Type I recovery. Only one patient had a prolonged stay in ICU, and another patient exhibited electrocardiographic evidence of a perioperative myocardial injury pattern. Selective intracavitary profound hypothermic arrest (15–18°C) (SIPHA) offered the best myocardial protection as evidenced by remarkably well preserved ultrastructure and significantly ( P< 0.005) lower post-bypass CK-MB levels (mean 7.85 U/L). All SIPHA patients had acceptable physiologic recovery trajectories of the Type I or Type II with minimal need for inotropic support (one patient), and none had a Type III recovery. These data also suggest that the major determinant of a successful myocardial preservation is the level of myocardial layer temperature, being best at the lowest temperature (15–18°C), worst at the highest temperature (30–33°C) and intermediate at 25–27°C. Additional injury may also be induced by ventricular fibrillation which by itself increases myocardial metabolic demands.