Controlled sequential pacing in isolated perfused auxiliary rat hearts

An important question after clinical auxiliary heart transplantation is whether controlled pacing of both hearts is desirable in order to protect the diseased recipient heart. A comparison of the effects of spontaneous beating with three types of pacing (random, simultaneous and sequential) was undertaken in an isolated perfused working double rat heart. The two hearts were attached to each other by the atria, in a way comparable to the clinical situation. During controlled sequential pacing of both normal hearts, the peak systolic pressure fell and diastolic pressure rose, but the combined cardiac output did not changes. In contrast, during simultaneous pacing, systolic pressure rose, diastolic pressure fell and coronary flow was less than with sequential pacing, but the oxygen uptake was higher. Hence the effects of sequential pacing could be expected to be beneficial when function of one of the hearts was depressed by left main coronary artery ligation. During sequential pacing the cardiac output was significantly improved from 10 to 30 ml/min (P less than 0.001) and coronary flow rose. Myocardial oxygen consumption increased from 80 to 110 microliters/g/min (P less than 0.05). Thus sequential pacing could improve the severely depressed hemodynamics of the coronary-ligated heart in the presence of an auxiliary heart. The increased myocardial oxygen consumption is viewed as a beneficial effect of increased diastolic perfusion pressure and was not associated with increased enzyme release. It is concluded that the effects of sequential pacing warrant assessment in clinical auxiliary heart transplantation.