Editorial Comment: Acute myocardial infarction and refractory cardiogenic shock: the simpler, the better?

Abstract

The excellent report by the Mount Sinai Medical Center Group [1] supports the concept of an immediate primary implantation of a long-term ventricular assist device (VAD), in patients in refractory cardiogenic shock because of an acute myocardial infarction (AMI). This primary implantation is probably preferable to more complex strategies, including the ‘bridge-to-bridge’ approach. It may be quite surprising that, after more than 30 years of experience, we are still wondering about the best option in these patients. The probable reason is that few papers focus on the specific issues of these AMI patients. There is actually still a wide variety of options. The most appealing option is the use of very small intraventricular devices (Tamdem, Impella ... ). They may be implanted with a non-invasive technique, under local anaesthesia, and even by the cardiologists who see the patients first and who try to apply some effective treatment such as percutaneous interventions. The device, ideally, should achieve full left ventricular decompression and deliver a pump output meeting the patient’s needs, so as to allow the recovery of peripheral organ function. The return to an adequate arterial pressure improves the coronary circulation, permitting some improvement of left ventricular function. Good left ventricular decompression enables the limitation of the acute myocardial infarct, by recovery of the borderline ischaemic myocardium. However, we currently lack this tiny pump that permits full left ventricular decompression and a return to normal aortic pressure. The available systems do not meet the requirements, in terms of ventricular decompression and pump flow. Moreover, they are also beset by other problems: difficulty in inserting the pump head into the left ventricle either from a peripheral artery, which is often atherosclerotic, or from a peripheral vein, since trans-septal catheterization may be hazardous in these unstable patients. Few papers have reported good results of this elegant approach. However, good results are usually seen in patients with less severe disease [2]. Finally, until now, we may say that great expectations have not been met. A second approach, totally different in its concept, is the use of extracorporeal membrane oxygenation (ECMO). The main advantages of this option are well known: it may be used almost everywhere, even outside a specialized centre, quite rapidly, without any surgical intervention, and is inexpensive. ECMO can therefore be instituted very early in the course of severe AMI. However, experience has shown that ECMO in AMI patients in cardiogenic shock does not fulfil the objectives as well as expected: the death rate during ECMO is quite high, whereas a low rate is quite seen in patients who can be stabilized or improved and receive a long-term VAD. The cost of ECMO also rises rapidly as the time spent in the intensive care unit increases. These less than satisfactory results are actually not that surprising: during ECMO, left ventricular unloading is less than optimal, making pulmonary recovery very unlikely, and right ventricular unloading is most often less than optimal, leading to persistent high venous pressure, which is unfavourable for the recovery of hepatic and renal function. In addition, activation of the inflammatory cascade, which is already stimulated by AMI, does not facilitate the recovery of pulmonary function. Finally, the lack of pulsatility does not help to improve renal and peripheral function. It is interesting to emphasize that the best results using ECMO support in irreversible cardiogenic shock are obtained in patients in whom cardiogenic shock is linked to reversible myocardial damage related, for example, to a toxic aetiology or acute myocarditis [3]. Results in AMI patients are less favourable: 5 of 16 AMI patients receiving urgent ECMO are discharged from the hospital, compared with a 56% overall success rate. Because of its simplicity and apparent low cost, ECMO is nevertheless still performed routinely, almost as a routine first treatment in patients in cardiogenic shock. However, in AMI patients, ECMO actually minimizes the chances of the patients getting a long-term VAD or a transplant. Our personal findings even show that replacement of ECMO by a pulsatile bi-VAD may reverse a situation, which is deteriorating on ECMO. A third approach is the use of pulsatile, paracorporeal VADs. The advantages of this technique are the quality of ventricular decompression, which is almost always complete and the rapid return to normal pulsatile perfusion. The versatility of the system permits either a left VAD or, in the case of additional right ventricular dysfunction, which is frequent in major AMI, temporary right ventricular support. This right ventricular support may be as short as a few days, permitting the recovery of right ventricular function and, in the meantime, avoiding the pulmonary embolic complications of long-term use. The limitation of this approach is obviously the discomfort of a long-term period of