Mechanical Circulatory Support With ECPR

Extracorporeal membrane oxygenation (ECMO) is increasingly used in critical care in patients whose conditions are deteriorating. Recently, ECMO use has extended to patients with refractory cardiac arrest, and a growing yet limited body of research shows that extracorporeal cardiopulmonary resuscitation (ECPR) improves mortality and meaningful neurologic recovery.¹ However, deleterious effects of venoarterial (VA) ECMO therapy, including retrograde blood flow from the aorta, can lead to distension of the left ventricle (LV) and ultimately pulmonary edema, blood stasis with thrombus formation, and increased oxygen demand.

While mechanical circulatory support devices, including Impella CP or Impella 5.5, are sometimes used while a patient is on ECMO, it may be of benefit to provide this support shortly after starting ECMO. There have been no randomized controlled trials comparing the outcomes of patients started on ECMO alone with those started on ECMO with an Impella device during ECPR.

Thevathasan et al conducted a first-of-its-kind meta-analysis using observational data to compare outcomes of patients with refractory cardiac arrest receiving VA ECMO only and those receiving VA ECMO along with subsequent Impella for LV unloading.² Their study included data from 32 hospitals and 1014 patients across rural and urban centers in multiple countries. The primary outcome was mortality, expressed as in-hospital mortality rate. Two other outcomes were good neurologic recovery, defined by a score of 1 or 2 on the Cerebral Performance Category Scale, and reported ECMO complications as defined by the Extracorporeal Life Support Organization.

The study cohort consisted of patients who met criteria for ECPR based on current international guidelines including a reversible cause of cardiac arrest, average low-flow time of 54 minutes, and pre-ECPR pH less than 7.1. Presenting diagnoses included acute myocardial infarction (MI), pulmonary embolism (PE), and miscellaneous causes of cardiac arrest.

The meta-analysis revealed that ECPR with Impella placement decreased in-hospital mortality (P = 0.023) and increased the likelihood of a good neurologic outcome (P = 0.015). More complications occurred when Impella was placed after ECMO (not statistically significant). A higher percentage of patients in the ECPR with Impella group had acute MI as the principal cause of cardiac arrest, whereas a higher percentage of patients in the VA ECMO group presented with PE and other causes. Importantly, a subgroup analysis of those presenting with acute MI revealed that ECPR with Impella had a 41% lower mortality than VA ECMO-only patients.

This study had many limitations. There was a wide range of mortality across different sites for both VA ECMO and ECMO with Impella. This wide range seems to be related to the size of the center and the volume of patients who undergo ECMO at each center, illustrating the importance of highly trained staff in significantly reducing mortality. Further, the two groups differed significantly in the number of patients, with the ECMO with Impella group having a higher ratio of patients presenting with acute MI as well as those presenting with a shockable rhythm, both of which are associated with improved survival compared to other cardiac arrest presentations. Finally, the specific version of Impella used and the amount of time it took to place each device were not recorded in the data.

While the limitations are important, this meta-analysis is a valuable study that will guide and inspire future trials investigating optimal ECPR practices. Although the cohorts had differing percentage of patients with acute MI and PE, the subgroup analysis showing decreased mortality rates and increased good neurologic outcomes in the acute MI group, indicating that there may be a target population that would benefit from ECMO and Impella. This study is a major step forward in the development of evidence-based guidelines for the use of mechanical circulatory support in ECPR.

References

1. Yannopoulos D, Bartos J, Raveendran G, et al. Advanced reperfusion strategies for patients with out-of-hospital cardiac arrest and refractory ventricular fibrillation (ARREST): a phase 2, single centre, open-label, randomised controlled trial. Lancet. 2020 Dec 5;396(10265):1807-1816.
2. Thevathasan T, Füreder L, Fechtner M, et al. Left-ventricular unloading with Impella during refractory cardiac arrest treated with extracorporeal cardiopulmonary resuscitation: a systematic review and meta-analysis. Crit Care Med. 2024 Jan 5. Online ahead of print.