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LV Unloading During Extracorporeal Membrane Oxygenation
Study Questions:
What is the impact of left ventricular (LV) unloading on mortality in patients supported with veno-arterial extracorporeal membrane oxygenation (VA-ECMO) for cardiogenic shock?
Methods:
The authors performed a systematic search of all studies in Medline, EMBASE, and Cochrane library from date of inception to August 2018. Included studies examined use of VA-ECMO for cardiogenic shock in adults and provided mortality data in patients with versus without LV unloading strategy. The primary outcome of interest was all-cause mortality. Additional analyses assessed impact of device used for LV unloading on mortality (intra-aortic balloon pump [IABP] vs. Impella vs. left atrial or pulmonary vein cannulation).
Results:
A total of 17 studies were included, with 3,997 cardiogenic shock patients on VA-ECMO: 1,696 (42%) with and 2,301 (58%) without LV unloading. All studies were retrospective, observational, and deemed of good or fair quality and two were published only as conference abstracts. No significant publication bias was noted. Mean age was 57 years with mean LV ejection fraction (LVEF) of 29.8% and baseline lactate of 7.2 µmol/L. The most common unloading strategy used was an IABP in 91.7%, followed by Impella in 5.5% and left atrial/pulmonary vein cannulation in 2.8% of patients. Patients receiving LV unloading devices were more likely to be men, and to have diabetes, chronic kidney disease, and cardiogenic shock due to acute ischemia.
Overall mortality was 60% during index hospitalization. LV unloading was associated with a significant reduction in mortality (relative risk [RR], 0.79; 95% confidence interval [CI], 0.72-0.87). There was no association between type of device (IABP vs. Impella) used for LV unloading and mortality (p = 0.83). There was no heterogeneity between LV unloading and reduced mortality in relation to etiology of cardiogenic shock. While rate of hemolysis was higher in patients with an LV unloading device (RR, 2.15; 95% CI, 1.49-3.11), rates of other complications such as bleeding, limb ischemia, stroke/transient ischemic attack, and multiorgan failure were similar between VA-ECMO patients treated with versus without LV unloading.
Conclusions:
In a systematic review of retrospective observational studies, use of LV unloading during VA-ECMO support for cardiogenic shock was associated with improved survival during index hospitalization. Apart from higher rates of hemolysis in patients receiving an LV unloading device, rates of other complications were similar.
Perspective:
VA-ECMO is the most widely used temporary mechanical circulatory support device and relies on retrograde aortic flow to improve organ perfusion, which results in increased LV afterload. In the setting of cardiogenic shock, increased afterload has deleterious consequences. High-quality evidence on the impact of LV unloading strategies in VA-ECMO patients with cardiogenic shock is lacking.
In this study, the authors conducted a meta-analysis of the best available literature in the form of retrospective observational studies to examine the association between mortality and LV unloading in VA-ECMO patients. Use of an LV unloading strategy in VA-ECMO patients was associated with a reduced mortality risk, irrespective of the type of device used for unloading and cause of cardiogenic shock. Furthermore, while rates of hemolysis were higher in patients receiving LV unloading devices, the incidence of other device-related complications was similar between the two groups.
Major limitations of this study are related to limitations of the studies included in the systematic review (i.e., selection bias in those who received LV unloading devices, presence of unmeasured confounders, and possible immortal time bias as patients received LV unloading devices after variable time lengths of being placed on VA-ECMO). In the absence of prospective randomized data, systematic review of existing retrospective studies suggests a mortality benefit of LV unloading strategy in VA-ECMO patients with cardiogenic shock without a concomitant increase in device-related complications.
Clinical Topics: Acute Coronary Syndromes, Arrhythmias and Clinical EP, Cardiac Surgery, Heart Failure and Cardiomyopathies, Atrial Fibrillation/Supraventricular Arrhythmias, Cardiac Surgery and Arrhythmias, Cardiac Surgery and Heart Failure, Acute Heart Failure, Mechanical Circulatory Support
Keywords: Acute Coronary Syndrome, Atrial Fibrillation, Diabetes Mellitus, Extracorporeal Membrane Oxygenation, Heart-Assist Devices, Heart Failure, Hemolysis, Intra-Aortic Balloon Pumping, Myocardial Ischemia, Renal Insufficiency, Chronic, Resuscitation, Shock, Cardiogenic, Stroke, Stroke Volume
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