Letter by Delmas et al Regarding Article, “Impella Support for Acute Myocardial Infarction Complicated by Cardiogenic Shock: Matched-Pair IABP-SHOCK II Trial 30-Day Mortality Analysis”
Authors: Clement Delmas, Marc Laine, Laurent Bonello
Journal: Circulation (2019)

We congratulate Schrage et al 1 for their comparison of Impella CP and intra-aortic balloon pump (IABP) in cardiogenic shock complicating acute myocardial infarction.In fact, cardiogenic shock remains a major challenge with a high mortality rate, and the current guidelines are based on a low level of evidence or on experts' opinions.At present, the main pitfall of the therapeutic strategy is to provide a sustained hemodynamic support to prevent or reverse organs dysfunction.For years, IABP use was based on limited evidence because it was the only device available.The results of the IABP-Shock 2 trial demonstrated that IABP was not beneficial, probably because of limited hemodynamic properties. 2 On the contrary, the Impella CP exhibited strong hemodynamic benefits and in observational studies was associated with an improved outcome. 3,4In our opinion, the present study has limitations that should be discussed because they may impair its ability to accurately evaluate the device.First, from a methodological and statistical point of view, this is a retrospective study that compares 2 unrelated cohorts: a registry and a group taken from a randomized trial.In addition to the limited level of evidence provided by such a design, in the statistical analysis, the matching procedures were not fully described, and critical differences between groups were not included in the matching without adjusted analysis, thus limiting the validity of the results.It must also be emphasized that the Kaplan-Meier and log-rank test presented do not account for matching of patients.Furthermore, although the authors provide subgroups analysis, their results are at most explanatory and do not substitute for accurate selection of patients and matching.Second, we believe that the selection criteria do not match the current consensus on the optimal care of cardiogenic shock complicating acute myocardial infarction, which could skew the results.Overall, up-to date consensus does not promote a device but rather a standardized therapeutic strategy with early mechanical circulatory support in very selected patients. 5Evidence suggests that door-to-support time and pre-percutaneous coronary intervention implantation of mechanical circulatory support are critical for success.In the present analysis, pre-percutaneous coronary intervention implantation of Impella was used in a limited number of patients, and door-to-support time was not taken into account.Furthermore, mechanical circulatory support should be restricted to selected patients, mostly those without a lengthy cardiac arrest and with a recovery potential or those who could benefit from a long-term project, unlike in the present analysis.Overall, propensity matching within a retrospective study as performed by the authors is unable to accurately evaluate such a standardized protocol of care with early mechanical circulatory support implantation for selected patients even with adjusted analysis.Therefore, in our opinion, the present analysis does not represent an accurate assessment of the standardized therapeutic strategy promoted by recent evidence.As acknowledged by the authors, a prospective randomized trial with accurate