Current status of diastolic augmentation for circulatory support

Abstract The hemodynamic effects of alteration of the aortic pressure pulse by diastolic augmentation in experimental acute myocardial infarction and clinical experience with these techniques are described. Both counterpulsation of blood in the aorta or femoral arteries and phased inflation of a thoracic aortic balloon achieve with reasonable predictability the physical aims of the procedure, i.e., diminution of the aortic systolic pressure and increment of the aortic diastolic pressure. However, varying hemodynamic consequences of these effects have been reported in experimental acute myocardial infarction with shock. Despite theoretical considerations, significant increase of the diminished coronary flow has not been found uniformly, particularly when the initial aortic pressure is quite low. Oxygen consumption of the myocardium usually, but not invariably, has been lowered by this technique and variable effects have been reported in reversing the anaerobic myocardial metabolic alterations of acute myocardial infarction. Analysis of the results indicates that the technique achieves optimal physiologic efficacy when it operates with a substrate of adequate central aortic pressure. This is accomplished more readily with balloon pumping than with central aortic counter-pulsation of blood alone, probably because of some circulatory compartmentalization produced by the balloon as well as by its central aortic pumping effects. In addition, balloon pumping as compared to counter-pulsation of blood affords the advantage of easier peripheral arterial cannulation and less destruction of the formed elements of the blood, thus allowing it to be used for longer periods. When the arterial pressure is quite low, additional efficacy can be obtained by utilizing the technique with a method to raise central aortic pressure by means of circulatory compartmentalization with a distal aortic balloon. The clinical results have been too sparse to form valid conclusions concerning the indications for and the ultimate hazerds and benefits of the techniques in acute myocardial infarction with shock. Most of the available experience has been with phasic inflation and deflation of a helium-filled thoracic aortic balloon. This has indicated a variable survival rate (about 30 per cent in the largest series) in patients refractory to conventional medical management. It is stressed that it is necessary to obtain more precise prognostic indications in acute myocardial infarction in the future so that optimum and reasonably early selection of patients who will not respond to other forms of therapy may be accomplished. This may permit initiation of circulatory support before irreversible cardiovascular deterioration has occurred.