Early left ventricular unloading via active transseptal left atrial venting in case of cardiogenic shock under veno‐arterial extracorporeal membrane oxygenation: A meta‐analysis
Authors: Aurore Ughetto, Safa Aouinti, Nicolas Molinari, François Roubille, Clément Delmas
Journal: European Journal of Heart Failure (2024)

While veno-arterial extracorporeal membrane oxygenation (VA-ECMO) is increasingly used as mechanical circulatory support for cardiogenic shock (CS) refractory to medical treatment, recent randomized controlled trials have all failed to demonstrate any benefit in terms of 30-day survival compared with optimal medical treatment in CS related to myocardial infarction.1 These disappointing results may partly be attributed to the substantial drawbacks of VA-ECMO support, including the retrograde continuous flow in the aorta leading to left ventricular (LV) overload and distension, increased myocardial workload and pulmonary oedema. To address these side effects and to facilitate VA-ECMO weaning, experts recommend early consideration of LV unloading after VA-ECMO initiation (class II, level C), without specifying the ideal strategy or optimal timing for implementation.2 One of the main strategies consists in left atrial (LA) venting either passive via an atrioseptostomy, or active via a cannula inserted through the interatrial septum and connected in 'y' to the venous line of the ECMO. In CS patients under VA-ECMO, two recent randomized trials3, 4 compared both an early routine active LA venting and a conventional approach with a rescue active LA venting in case of pulmonary oedema. However, these trials were probably underpowered to adequately assess their primary endpoint. That's why, we performed a pooled data meta-analysis to reassess the benefit of early LA venting. Pooled odds ratios and their 95% confidence intervals were used for categorical outcomes. Heterogeneity, assessed by Higging's I2-index, deemed acceptable at I2 < 50%, led to a fixed-effects model application. Analyses were two-tailed, with statistical significance at p < 0.05. Statistical analysis employed R software with the 'meta' (v. 6.5-0) package. A total of 176 patients were randomized to either early LV unloading (n = 88) or conventional approach (n = 88) (online supplementary Table Appendix S1). As reported in Figure 1, there was no difference in in-hospital mortality, weaning from VA-ECMO and bridge to durable ventricular assist device or heart transplantation. In addition, there were no significant differences in adverse events between early LV unloading and conventional approach including stroke (16% vs. 10%), limb ischaemia (8% vs. 9%), tamponade (3% vs. 1%), bleeding (16% vs. 20%) (online supplementary Figure Appendix S1). Given identical inclusion criteria, comparable LA venting techniques, and a similar randomization process, our results confirm that early active LA venting does not offer prognostic advantages for VA-ECMO-supported CS patients compared to the conventional approach using LA venting in case of pulmonary oedema. Considering our findings, specific points deserve careful consideration. First, the efficacy of LA venting for effective LV unloading remains debatable, especially in situations without significant mitral regurgitation. This technique only focusing on LV preload neglects the intricate contributions of venous return through Thebesian veins, bronchial veins, and retro-aortic circulation—factors that become prominent in cases involving aortic regurgitation, which is often favoured by ECMO. LA venting is associated with a risk of inadequate drainage and an increased risk of LV or aortic root thrombus formation in the absence of aortic valve opening. Furthermore, the benefit–risk ratios of active or passive LA venting are probably different. The atrioseptostomy seems to be a cost-effective and available alternative, potentially reducing complications without introducing artificial components, but with an unpredictable transseptal shunt flow and uncertain durability. Additionally, a further limitation of this approach arises from the fact that the LA cannula is naturally explanted during VA-ECMO removal, potentially posing challenges for providing assistance during the crucial weaning period. Thus, LA venting could make sense for patients with LV thrombus, to avoid a second femoral arterial access or for patients on VA-ECMO with mitral regurgitation. Secondly, the optimal timing and device choice seem to be key factors. To date, retrospective data suggest that early initiation of LV unloading by percutaneous left ventricular assist devices (pLVAD) (<2 h) may reduce short-term mortality.5 Conversely, our finding failed to validate these advantages with early LA venting despite a very quick device placement (median: 2.4 h). This contradictory result underscores that device choice could influence outcomes. As a compelling alternative, intra-aortic balloon pump or pLVAD are increasingly used to LV unloading in combination with VA-ECMO. The distinct pathophysiological mechanisms of these strategies highlight the importance of further research comparing these different approaches. Lastly, we have to acknowledge some limitations. Given the low merged power, the likelihood of achieving statistical significance in survival improvement would have necessitated a more than 45% reduction in mortality, a biologically unlikely scenario given the actual mortality in the two studies. In conclusion, although lack of power might still be an issue despite merging data from two randomized controlled trials, current evidence does not support an early and routine use of LA venting in patients on VA-ECMO. Future studies are needed to determine whether this is because the chosen method or the application of unloading in general are futile treatment strategies for these patients. Conflict of interest: F.R. reports honoraria for lectures from AstraZeneca, Servier, Boehringer Ingelheim, AstraZeneca, Vifor, Bayer, Pfizer, Novartis, Servier, NovoNordisk, Air Liquide, Abbott, QuidelOrtho. C.D. report lectures fees from Abiomed and Abbott. All other authors have nothing to disclose. Appendix S1. Supporting Information. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.