Novel Role for Cardiolipin as a Target of Therapy to Mitigate Myocardial Injury Caused by Venoarterial Extracorporeal Membrane Oxygenation

BACKGROUND

Cardiolipin is a mitochondrial-specific phospholipid that maintains integrity of the electron transport chain (ETC) and plays a central role in myocardial ischemia/reperfusion injury. Tafazzin is an enzyme that is required for cardiolipin maturation. Venoarterial extracorporeal membrane oxygenation (VA-ECMO) use to provide hemodynamic support for acute myocardial infarction has grown exponentially, is associated with poor outcomes, and is under active clinical investigation, yet the mechanistic effect of VA-ECMO on myocardial damage in acute myocardial infarction remains poorly understood. We hypothesized that VA-ECMO acutely depletes myocardial cardiolipin and exacerbates myocardial injury in acute myocardial infarction.

METHODS

We examined cardiolipin and tafazzin levels in human subjects with heart failure and healthy swine exposed to VA-ECMO and used a swine model of closed-chest myocardial ischemia/reperfusion injury to evaluate the effect of VA-ECMO on cardiolipin expression, myocardial injury, and mitochondrial function.

RESULTS

Cardiolipin and tafazzin levels are significantly reduced in the left ventricles of individuals requiring VA-ECMO compared with individuals without VA-ECMO before heart transplantation. Six hours of exposure to VA-ECMO also decreased left ventricular levels of cardiolipin and tafazzin in healthy swine compared with sham controls. To explore whether cardiolipin depletion by VA-ECMO increases infarct size, we performed left anterior descending artery occlusion for a total of 120 minutes followed by 180 minutes of reperfusion in adult swine in the presence and absence of MTP-131, an amphipathic molecule that interacts with cardiolipin to stabilize the inner mitochondrial membrane. Compared with reperfusion alone, VA-ECMO activation beginning after 90 minutes of left anterior descending artery occlusion increased infarct size (36±8% versus 48±7%; P<0.001). VA-ECMO also decreased cardiolipin and tafazzin levels, disrupted mitochondrial integrity, reduced electron transport chain function, and promoted oxidative stress. Compared with reperfusion alone or VA-ECMO before reperfusion, delivery of MTP-131 before VA-ECMO activation reduced infarct size (22±8%; P=0.03 versus reperfusion alone and P<0.001 versus VA-ECMO alone). MTP-131 restored cardiolipin and tafazzin levels, stabilized mitochondrial function, and reduced oxidative stress in the left ventricle.

CONCLUSIONS

We identified a novel mechanism by which VA-ECMO promotes myocardial injury and further identify cardiolipin as an important target of therapy to reduce infarct size and to preserve mitochondrial function in the setting of VA-ECMO for acute myocardial infarction.

The Case Number Changes in Adult Heart Transplantation and Waitlist Addition Due to COVID-19

Purpose

To understand the long term effect of COVID-19 on 1) heart transplant waitlist trends and on 2) heart transplant case numbers in the United States.

Methods

The number of new adult heart transplant waitlist additions and transplant procedures were obtained from the UNOS database. Our time frame includes the 52 weeks between September 3, 2019 and September 4, 2020. Temporal changes in waitlist additions and heart transplants were analyzed using interrupted time series analyses with two transition periods. The first transition from the pre-COVID to the post-COVID era was determined as the week of March 11, 2020, when the first state imposed stay-at-home orders. The second transition period was determined as the first state re-opening during the week of April 22, 2020.

Results

Weekly waitlist additions were decreasing at -0.19 additions per week (95% CI: -0.35 to -0.03, p=0.018) prior to the COVID-19 era, defined as before the week of March 11, 2020, with a significant decrease in weekly waitlist additions of -2.09 (95% CI: -2.44 to -1.73, p< 0.001) during the post-COVID-19 era and prior to the first state re-opening the week of April 22, 2020 (Figure A). Weekly waitlist additions increased at 2.16 additions per week (95% CI: 1.81 to 2.51, p<0.001) following the first state announcing re-opening the week of April 22, 2020.

Weekly transplants were relatively unstable, although decreasing at -0.003 transplants per week (95% CI: -0.279 to 0.273, p=0.984) in the pre-COVID era, and were trending downward at -0.18 transplants per week (95% CI: -0.3702 to 0.0036, p=0.054) thereafter (Figure B). The number of transplants rebounded and increased significantly at 0.49 transplants per week (95% CI: 0.26 to 0.72, p<0.001) after April 22, 2020.

Conclusion

The number of heart transplants and waitlist additions decreased significantly due to COVID-19 and rebounded following the first US state reopening the week of April 22, 2020. Waitlist additions continue to rise past levels observed during the pre-COVID era.