The Starling Relationship and Veno-Arterial ECMO: Ventricular Distension Explained

Abstract

The use of veno-arterial (VA) extracorporeal membrane oxygenation (ECMO) to support patients with acute heart failure has been associated with ventricular distension and pulmonary edema, the mechanism of which is not fully understood. This study examined the impact of VA ECMO on left ventricular (LV) Starling curves to elaborate a framework for anticipating and treating LV distension. A previously developed and validated model of the cardiovascular system was used to generate pressure-volume (PV) loops and Starling curves while holding mean arterial pressure (mABP) constant at a range of values either by adjusting systemic resistance or by adding VA ECMO support. It was found that under all conditions of similar mAPB, the Starling curve was unchanged; therefore, the degree of LV distension is obligated by the mAPB (irrespective of whether controlled pharmacologically with or without ECMO support and independent of heart rate), LV contractility, and target stroke volume. The Starling relationship provides a conceptual framework for understanding the risk and treatment of LV distension during VA ECMO support.

Left Ventricle Unloading with Veno-Arterial Extracorporeal Membrane Oxygenation for Cardiogenic Shock. Systematic Review and Meta-Analysis

“…If peripheral resistance and LV contractility are fixed, increase in LV end-diastolic volume is the only way to overcome the afterload via the Frank-Starling mechanism. In this case, higher levels of VA-ECMO flow cause a progressive rise in LV end-diastolic pressure, LA pressure, pulmonary capillary wedge pressure, that are associated with a further reduced LV stroke volume [26][27][28]. High afterload situations with inability of LV to manage the transpulmonary blood flow, inadequate response to inotropes, complete cardiac arrest with incomplete venous drainage and aortic valve incompetence are the commonest risk factors for LV distension.…”

Extracorporeal Membrane Oxygenation: The New Jack-of-All-Trades?

“…72 Blood in the LV must exit through the aortic valve, necessitating the struggling LV to eject against arterial pressure that is increased by VA-ECMO flow. 91 With increasing ECMO flows, the stroke volume may decrease to a volume less than the volume returning to the left ventricle. 72 Stasis of blood in the LV can lead to thrombosis (LV, aortic, pulmonary).…”

“…Thus LV venting strategies to avoid events related to LV distention are an essential component of VA-ECMO and are listed in Table 14. 72,91,93,94 Intra-aortic balloon pump improves LV distention by increasing stroke volume with some unloading effect, which could be beneficial in the setting of a persistently non-ejecting LV. 94 The challenge of atrial septostomy is creating an appropriately sized, well-defined defect.…”

Flow Optimization, Management, and Prevention of LV Distention during VA-ECMO

“…LV afterload before ECMO is related to systemic arterial pressure, and the Starling curve generated before initiation of ECMO flow predicts the filling pressure associated with any target SV at that systemic pressure. The addition of ECMO flow or alterations solely in SVR does not alter the relationship between filling pressure and native LV SV, and then the abrupt increase of afterload due to the ECMO flow may be useful to predict ventricular distension during ECMO support [32].…”