Effects of retrograde cardioplegia on myocardial perfusion and energy metabolism in immature porcine myocardium

Objectives: Retrograde cardioplegia has been widely used for the protection of adult hearts during cardiac operations. Its efficacy to protect immatur e myocardium is still unclear. This study was designed to assess the effect s of retrograde cardioplegia on myocardial perfusion and energy metabolism in immature hearts. Methods: Piglet hearts were divided into 3 groups. Hearts in group 1 were u sed to assess myocardial perfusion of retrograde cardioplegia by means of m agnetic resonance imaging. Hearts in groups 2 and 3 were used to assess the effects of retrograde cardioplegia on myocardial energy metabolism by use of phosphorus 31 magnetic resonance spectroscopy. Results: Magnetic resonance images showed that perfusion with retrograde ca rdioplegic solution was heterogeneous. A perfusion defect was noted during retrograde cardioplegia in the right ventricular wall and in a portion of t he posterior wall of the left ventricle in 4 of 6 hearts. Phosphorus 31 spe ctra showed that at the end of 45-minute retrograde cardioplegia, myocardia l intracellular pH was 6.83 +/- 0.17 and phosphocreatine was 53.5% +/- 27% of its prearrest value. The adenosine triphosphate level, however, remained normal throughout the retrograde cardioplegia period. Last, the hearts sub jected to retrograde cardioplegia or antegrade cardioplegia showed similar and complete metabolic and functional recovery during reperfusion. Conclusions: Retrograde cardioplegia provides heterogeneous perfusion. Its ability to protect the right ventricular myocardium is poor and varies betw een individuals. Myocardial perfusion provided by retrograde cardioplegia i s slightly less than that needed to sustain normal myocardial energy metabo lism under normothermic conditions.