Interpreting National Databases on Mechanical Circulatory Support

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We read with great interest the article published in a recent issue of Critical Care Medicine by Aso et al (1) discussing the use of intra-aortic balloon pump (IABP) on patients with cardiogenic shock receiving venoarterial extracorporeal membrane oxygenation (VA-ECMO) support. They concluded that patients with cardiogenic shock who received IABP support during VA-ECMO had lower overall 28-day and in-hospital mortality and a higher probability of successful weaning from VA-ECMO, using a propensity match to correct for patient group differences. We commend them on their efforts of utilizing a national database to evaluate the utility of dual mechanical circulatory support (MCS) in these complex patients.
In order to apply these findings in clinical practice, we would be interested in further data regarding illness severity to demonstrate whether patients receiving an IABP differed from those who did not in terms of shock or multiple organ failure severity. To better interpret these results, we hope the authors can provide severity of illness scores (i.e., cardiovascular Sequential Organ Failure Assessment score) or inotrope dosing scores (i.e., Inotrope Score) in both groups, since hemodynamics at the time of instituting ECMO can predict overall outcomes (2, 3). Likewise, it would be important to know prevalence of predictors of survival in patients with cardiogenic shock, such as end-organ hypoperfusion (serum lactate levels and urine output), anoxic brain injury, stroke work, and location of myocardial infarction (4). Using clinical variables, Schmidt et al (5) proposed a Survival After VA-ECMO (SAVE) score that predict survival in patients undergoing VA-ECMO. It would be interesting to compare SAVE scores between the two cohorts and evaluate their addition to the current propensity-matching algorithm to determine whether the IABP remains independently associated with mortality. The presented data leave uncertainty as to whether the non-IABP cohort was sicker at baseline, which would potentially influence the differences in outcomes.
Certain nonmortality clinical outcomes merit inclusion in a study involving MCS in cardiogenic shock. In those patients without myocardial recovery, it would be worthwhile to know rates of durable MCS implantation or cardiac transplant. Rates of ECMO weaning were reported, yet the use of these exit strategies will be important to know to understand these results. In addition, no data are presented regarding rates of device-related complications and whether these were influenced by addition of the IABP. Without these additional data, our understanding of the outcomes of combination MCS in cardiogenic shock is incomplete necessitating further deliberation.
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