Review ArticleLeft Ventricular Unloading During Extracorporeal Life Support: Current Practice
Section snippets
Indications for VA-ECLS in CS
Whereas VA-ECLS was originally intended to provide temporary mechanical support during cardiac surgery, its indications have expanded rapidly over the past decade.10,11 VA-ECLS has been successfully used to treat CS of various causes, including acute myocardial infarction, refractory ventricular tachycardia, acute decompensated heart failure, and fulminant myocarditis.2,5 In recent times, VA-ECLS has also been shown to improve outcomes in patients with refractory cardiac arrest (as
Hemodynamic Effects of VA-ECLS and the Usefulness of LV Venting
CS is defined by hypotension (unsupported systolic blood pressure of <90 mm Hg for ≥30 minutes), decreased cardiac index (<2.2 L/min/m2), and elevated left-sided pressures (pulmonary capillary wedge pressure [PCWP] of >15 mm Hg) in the presence of end-organ hypoperfusion.15 Fig. 1A shows a pressure–volume loop that illustrates the function of a normal heart.16 In CS, the pressure–volume loop shifts to the right as contractility decreases and filling volumes increase in an attempt by the heart
Timing and Patient Selection for LV Venting
Optimal patient selection and timing for LV venting remains uncertain because few robust prospective studies have evaluated this question.27,28 Commonly cited indications for LV venting include LV distension, an elevated PCWP, a low or absent pulse pressure, a lack of aortic valve opening, North–South syndrome, pulmonary edema, and lung injury.5, 6, 7,11 Computational modeling has identified low ejection fraction and elevated PCWP before ECLS initiation as important predictors of LV distension,
Optimization of LV Unloading
For maximal benefit, LV venting must provide optimal LV unloading. There is no clear consensus on what constitutes optimal LV unloading, Several modalities are available to measure LV unloading, including intracardiac pressures with a PAC, echocardiography, measuring biomarkers of LA distension such as brain natriuretic peptide, and assessing end-tidal CO2 in intubated patients. Simulation studies aim to better estimate the optimal parameters of LV unloading in ECLS.33
Although the value of a
Duration of LV Venting
Several questions remain about the optimal time to discontinue LV venting. Several centers that used a combination of extracorporeal membrane oxygenation and Impella P-VAD support (termed “ECMELLA”) as their venting modality describe a strategy of leaving the P-VAD in place to facilitate weaning completely off VA-ECLS, then slowly weaning the P-VAD support.19,25 One meta-analysis showed that the continued use of an LV vent throughout was associated with higher rates of successful weaning from
Effectiveness of Specific LV Venting Strategies
Multiple strategies have been used to offload the LV, including medical unloading (eg, with inotropes, vasodilators, or diuretics), decreasing arterial ECLS flows, IABP, ECMELLA, atrial septostomy, and surgical venting.6,20, 21, 22,24,41,42 As discussed elsewhere in this article, no one solution is ideal; medical unloading may be insufficient because the use of inotropes can further increase myocardial oxygen demand, especially in patients who may not tolerate a decrease in ECLS flow.9,11 Thus,
Challenges Associated With LV Venting
LV venting incurs certain risks, which vary with the type of LV vent used. A large meta-analysis of patients vented while on VA-ECLS (primarily with IABP, but ECMELLA was used in some cases) showed that vented patients had higher rates of hemolysis; there were no other differences in secondary outcomes, including bleeding. Similar findings were seen in a study of ECMELLA patients, who had better survival than patients with no LV venting despite having higher rates of hemolysis and renal
Weaning LV Venting and VA-ECLS Support
In the decision to wean temporary MCS, including VA-ECLS, the central criterion is adequate myocardial recovery to support metabolic demands. Readiness-to-wean criteria as defined by the Extracorporeal Life Support Organization include improved arterial pulsatility and cardiac contractility, minimal vasoactive agent use to maintain a mean arterial pressure or greater than 60 mm Hg, and adequate oxygen delivery.66 Including hemodynamic assessment (central venous pressure of ≤15 mm Hg, PCWP of
Future Studies: More Data Needed
Although conducting randomized trials in CS is difficult, many questions remain regarding LV venting in VA-ECLS. There is an urgent need to obtain further data regarding almost all aspects of LV venting, including identifying which patients will benefit from LV venting, defining the optimal technique for LV offloading for specific populations according to the cause of their CS, determining the optimal timing and goals of LV venting, identifying the best weaning strategies, and even examining
Comprehensive CS Management
CS remains one of the leading indications for cardiac intensive care unit admission, and caring for these patients is complex and resource intensive.72 Core competencies of a cardiac intensive care unit caring for patients with CS include the ability to characterize and diagnose CS, rapidly place and maintain a variety of temporary MCS devices including VA-ECLS, and a multidisciplinary shock team. Owing to paucity of randomized controlled trials guiding the care of patients with CS supported
Conclusions
VA-ECLS is an extraordinary tool in the contemporary management of CS, although it is a tool whose use carries the risk of impairing myocardial recovery and worsening pulmonary function because of retrograde aortic perfusion. LV venting represents a means of limiting these complications of VA-ECLS, but venting itself presents unique challenges. Further research will be necessary to improve patient selection and define optimal strategies to offload the LV in VA-ECLS.
Conflict of interest
None.
Acknowledgments
Stephen N. Palmer, PhD, ELS, of the Department of Scientific Publications at the Texas Heart Institute, contributed to the editing of the manuscript.
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