Temporary left ventricular assistance in acute myocardial infarction and cardiogenic shock. Rationale and criteria for utilization

Left ventricular bypass may offer significantly better salvage of left ventricular myocardium in patients who remain hemodynamically unstable in spite of aggressive medical therapy and intra-aortic balloon support. Indeed, those 25 percent of patients refractory to intraaortic balloon pumping may be salvageable with the prompt institution of left ventricular pumping assistance; however, just as early initiation of intra-aortic balloon pumping is critical, the early identification of balloon pumping failures and the institution of left ventricular bypass pumping may lead to a lower incidence of patients dependent on circulatory assistance and a higher rate of primary weaning. The results of left ventricular pumping assistance may indeed be totally different than those achieved with the intra-aortic balloon pump under these same conditions, because of the marked left ventricular unloading and hence the greater reduction in myocardial consumption of oxygen. The self-perpetuating cycle of progressive irreversible cardiac damage and shock may be broken, resulting in salvage of critical myocardial mass. Thus, cases of pumping dependence may be uncommon. There is also reason to believe that the heart without anatomically correctable lesions might function satisfactorily, but with a low cardiac reserve. Successful clinical application of left ventricular pumping assistance and subsequent analysis of therapeutic results demand a carefully devised protocol. This must be based on knowledge of the natural history of the disease and the results of previous sound clinical and experimental studies.