Myocardial energy metabolism during mitral valve replacement

To elucidate the metabolic changes during a relatively short ischemic period, papillary muscle excisions were investigated in 38 patients operated for mitral valve replacement. The overall mean age was 62 years, in 27 women and 11 men. Two excisions were made during ischemia, the first after 13 minutes and the second after 48 minutes of aortic occlusion. These excisions were analyzed for adenine nucleotide, creatine phosphate, lactate and pyruvate contents. The results indicated an ongoing metabolism with an accumulation of lactate, and also influences on the energy charge. For example, although the content of ATP was unchanged between the excisions, the relation to creatine phosphate, as a source for ATP level maintenance, was altered. This is of clinical importance since cardioplegia and hypothermia (myocardial temperature below 20 degrees C) were employed and the interval between the excisions was only 35 minutes on average. Although no significant decrease in myocardial ATP took place, 31 of 38 patients needed inotropic support to wean them off bypass. On the basis of the present results further efforts seem necessary to improve myocardial preservation techniques.