Variability in triggers for mechanical left ventricular unloading in VA-ECMO: A literature search

Background: Venoarterial Extracorporeal Membrane Oxygenation (VA-ECMO) is a means of supporting the lungs or the heart and lungs in patients with hemodynamic compromise that is refractory to conventional measures. VA-ECMO is most commonly deployed in a percutaneous fashion with femoral arterial and venous access. While VA-ECMO, particularly in a femoral-femoral configuration, provides both hemodynamic and ventilatory support, it also causes increased afterload on the left ventricle (LV) which in turn may result in LV distension (LVD). LV thrombus formation, ventricular arrhythmias, pulmonary edema, and pulmonary hemorrhage are clinical manifestations of LVD. LV unloading is a means of preventing LVD and its sequelae. If less invasive methods fail to achieve adequate LV unloading, invasive mechanical methods are pursued such as intra-aortic balloon pump counter-pulsation, atrial septostomy, surgical venting, left atrial cannulation, and percutaneous transvalvular micro-axial pump placement. Methods: We sought to review indicators of LVD, thresholds, and options for mechanical venting strategies. A Pubmed search was performed to identify current literature about LV unloading for VA ECMO. This was categorized and summarized to determine commonly reported thresholds for mechanical LV unloading. Results: Multiple physiologic and radiographic indicators were reported without uniformity. Common indicators included increased pulmonary artery catheter pressures, decreased Aortic Line Pulse Pressure, as well as multiple Echocardiographic, and radiographic indicators. Conclusion: Although there has been significant interest in the topic, there is currently limited uniformity in thresholds for when to initiate and escalate mechanical LV unloading. While the method of LV unloading is an active area of investigation, the threshold for which to initiate invasive venting strategies is largely unexplored.