Clinical impact of intra-aortic balloon pump during extracorporeal life support in patients with acute myocardial infarction complicated by cardiogenic shock

The mortality rate for acute myocardial infarction (AMI) complicated by cardiogenic shock appears to be unchanged at about 40-50% after the introduction of primary percutaneous coronary intervention (PCI) and an intra-aortic balloon pump (IABP) [1‐3]. Accordingly, new mechanical-assist devices are being developed to maintain hemodynamic support in cardiogenic shock. Extracorporeal life support (ECLS) can be placed percutaneously and initiated quickly, making it helpful in emergencies [4]. ECLS, however, has an essential limitation: it is only able to partially unload the left ventricle (LV), and LV afterload may be high [5]. IABP may be an option to optimize hemodynamic status during ECLS and to reduce afterload and increase diastolic augmentation with an improvement in coronary perfusion [6]. There is limited data, however, about clinical outcomes of simultaneous IABP support and ECLS in AMI patients complicated by cardiogenic shock. Here, we report outcomes of this combination therapy.

We investigated whether additional IABP is associated with improved in-hospital survival in patients with AMI and complicating cardiogenic shock who underwent ECLS. The combined use of ECLS and IABP did not improve in-hospital survival or tissue hypoperfusion. The additional IABP insertion did not increase vascular complications or bleeding.

An IABP improves coronary and peripheral perfusion via diastolic balloon inflation and augments LV performance via systolic balloon deflation, with an acute decrease in afterload [10]. The effects of IABP during ECLS, however, have not been evaluated sufficiently. An experimental study suggested that IABP-induced pulsatility improves coronary bypass graft flows during nonpulsatile ECLS [11]. Another study proposed that adjunctive IABP improves the myocardial oxygen supply–demand balance in peripheral extracorporeal life support [12]. These benefits of IABP might increase coronary flow during diastole and compensate for limitations of ECLS, such as myocardial oxygen consumption associated with increased LV afterload. Consequently, the concomitant use of IABP might improve in-hospital survival during ECLS management. In our study of patients with AMI and complicating cardiogenic shock, however, combined IABP support during ECLS did not reduce in-hospital mortality. A recent study in Korea also showed that the concomitant use of IABP did not reduce hospital mortality despite an improved success rate in weaning from ECLS [13]. The most likely explanation about different successful weaning rate involves patient selection. Our patients had a higher incidence of cardiac arrest compared to that in the previous study (63.5% vs. 31.6%). A large proportion of patients in their study (46.6%) were enrolled for low cardiac output after cardiac surgery, and it is therefore difficult to compare their results directly to ours.

To the best of our knowledge, there have been no well-designed trials to explain why there are no significant differences between mortality in the two groups. We considered the possibility that coronary blood flow might not increase enough to cause haemodynamic changes after using IABP under continuous flow from ECLS into the human circulating system. There were no significant differences in haemodynamic variables, such as cardiac output, between the patients supported by IABP and the patients treated with medical therapy in a recent randomized trial, although that study was conducted without ECLS management [14]. Furthermore, the IABP balloon may cause intermittent aortic occlusion, which may diminish the blood flow from ECLS to the aortic root and coronary arteries. An experimental study demonstrated that, in the setting of cardiac arrest, the addition of IABP to ECLS might worsen coronary blood flow [15].

Because lactate clearance early in hospital care may indicate a resolution of global tissue hypoxia [16], we compared the lactate clearance for 48 hours between the ECLS/IABP group and the ECLS alone group to evaluate the effectiveness of IABP for aiding recovery from tissue hypoperfusion during cardiogenic shock. Lactate clearance for 48 hours, however, was similar regardless of the combined use of IABP. This finding suggests that additional IABP support is unlikely to be useful in the early recovery from severe cardiogenic shock.

Our study had several limitations. First, it was a retrospective, observational study; therefore, confounding factors may have significantly affected our results. Hidden biases for the initiation of mechanical-assist devices might exist because the attending physician in charge decided whether to use ECLS alone or with IABP. Furthermore, the ECLS/IABP group included patients who were initially supported by IABP alone and later also received ECLS. Our hypothesis was that the effect of LV unloading by IABP during ECLS might improve survival. Therefore, patients were placed in the ECLS/IABP group if they were supported by the IABP during ECLS, regardless of the implantation order. Second, our registry did not include pulmonary capillary wedge pressure measured by pulmonary arterial catheter, LV size, or E/e’ measured by echocardiography. This haemodynamic information might support the hypothesis of IABP’s effect on LV unloading. Third, performance of CPR, which has been reported as an important predictor of mortality in patients with severe cardiogenic shock [17, 18], was significantly different between the two groups. In addition, a larger number of patients treated with only medical therapy without revascularization were included in the ECLS alone group, and a larger number of patients who had undergone bypass surgery were included in the ECLS/IABP group. Efforts were made to compensate for these differences in the multivariable analysis, but we may not have been able to overcome the differences. Fourth, our data included a large number of patients who underwent CPR and thus showed a higher mortality than in another recent randomized trial and a registry of cardiogenic shock [3, 19]. Even if there are minor benefits of IABP support, additional effects might not be evident in patients with very severe cardiogenic shock. As there have been no other clinical studies regarding the use of IABP during ECLS, our study provides the first information about modalities of AMI shock treatment. A large registry study or randomized trial, however, is needed for a more complete assessment of the role of IABP during ECLS.

Additional use of IABP during ECLS did not improve in-hospital survival or tissue perfusion in patients with AMI complicated by cardiogenic shock.