The effects of retrograde cardioplegia technique on myocardial perfusion and energy metabolism: A magnetic resonance imaging and localized phosphorus31 spectroscopy study in isolated pig hearts

Objective: The present work was designed to study the myocardial perfusion and energy metabolism during retrograde cardioplegia performed with differe nt methods, including deep coronary sinus cardioplegia, coronary sinus orif ice cardioplegia, and right atrial cardioplegia. Methods: Isolated pig hearts were subjected to antegrade cardioplegia, righ t atrial cardioplegia, deep coronary sinus cardioplegia, and coronary sinus orifice cardioplegia in a random order. Cardioplegic distribution was asse ssed by T1-weighted magnetic resonance imaging in 1 group of hearts (n = 8) . The flow dynamics of cardioplegia were assessed by T2*-weighted imaging i n a second group of hearts (n = 8). Results: T1-weighted images revealed an apparent perfusion defect in the po sterior wall of the left ventricle, the posterior portion of the interventr icular septum, and the right ventricular free wall during deep coronary sin us cardioplegia. The perfusion defect observed in the first 2. regions with deep coronary sinus cardioplegia resolved with coronary sinus orifice card ioplegia. Right atrial cardioplegia provided the most homogeneous perfusion to all regions of the myocardium relative to the other 2 retrograde cardio plegia modalities. T2*-weighted images showed that the 3 retrograde cardiop legia modalities provided similar cardioplegic flow velocities. Localized p hosphorus 31 spectroscopy showed that the levels of adenosine triphosphate and phosphocreatine were significantly lower in the posterior wall (adenosi ne triphosphate, 42.86% +/- 5.91% of its initial value; phosphocreatine, 11 .43% +/- 11.3%) than the anterior wall (adenosine triphosphate, 89.19% +/- 8.83%; phosphocreatine, 59.54% +/- 12.58%) of the left ventricle during 70 minutes of normothermic deep coronary sinus cardioplegia, Conclusions: Deep coronary sinus cardioplegia results in myocardial ischemi a in the posterior wall of the left ventricle and the posterior portion of the interventricular septum, as well as in the right ventricular free wall. Coronary sinus orifice cardioplegia improves cardioplegic distribution in these regions. Relative to deep coronary sinus cardioplegia and coronary si nus orifice cardioplegia, right atrial cardioplegia provides the most homog eneous perfusion.