Is pulmonary artery (PA) venting considered a right ventricular assist device (RVAD) in a patient with severe right ventricular failure on veno-arterial (VA) extracorporeal membrane oxygenation (ECMO)?

Is PA Venting Considered an RVAD?

No, pulmonary artery (PA) venting is not considered a right ventricular assist device (RVAD), but rather represents a distinct mechanical circulatory support strategy with fundamentally different hemodynamic effects and clinical applications.

Fundamental Mechanical Differences

RVADs and PA venting systems operate through completely opposite mechanisms:

• Traditional RVADs have inflow cannulas in the right atrium and outflow cannulas in the pulmonary artery, pumping blood from the RA into the PA, which paradoxically increases pulmonary artery pressures and pulmonary capillary wedge pressures in patients with elevated pulmonary vascular resistance 1

• PA venting systems drain blood from the pulmonary artery and return it either to the venous circulation (creating a hybrid ECMO configuration) or to the left atrium (as with lung assist devices), thereby decompressing the pulmonary circulation rather than increasing pressures 2

Clinical Context: The VA ECMO Problem

The need for PA venting arises specifically in the context of VA ECMO-related complications:

• VA ECMO increases RV afterload by raising systemic arterial pressure, which increases RV wall stress and oxygen demand 2

• Blood pumped into the pulmonary circulation by residual RV function encounters a "dead-end" because the left heart is already filled by ECMO flow, causing pulmonary artery pressures to rise dramatically 2

• This leads to progressive RV distension, worsening tricuspid regurgitation, and critically, pulmonary hemorrhage from vascular rupture due to excessive pulmonary artery and capillary pressures 2

PA Venting as a Decompression Strategy

PA venting is indicated when pulmonary artery pressures remain dangerously elevated despite VA ECMO support:

• The American College of Cardiology recommends PA venting to decompress the pulmonary circulation and prevent pulmonary capillary pressures from reaching hemorrhagic levels 2

• Evidence of pulmonary hypertension (sPAP >40 mmHg) or acute cor pulmonale on echocardiography indicates the need for PA venting on VA ECMO 2

• Rising pulmonary artery pressures despite VA ECMO support, indicating inadequate RV ejection, signals that PA venting may be necessary 2

Technical Implementation Options

Several distinct approaches exist for PA venting, none of which function as traditional RVADs:

• Direct PA cannulation with drainage to the venous side of the ECMO circuit creates a hybrid configuration that decompresses the pulmonary circulation 2

• Venopulmonary artery ECMO (VPA-ECMO) places an inflow cannula in the right atrium via femoral vein and outflow cannula in the left pulmonary artery via internal jugular vein, effectively creating an "oxyRVAD" configuration 3, 4

• Lung assist devices (LAD) like Novalung® connect the main PA to the left atrium in parallel (not in series like RVADs), creating a shunt that bypasses the high-resistance pulmonary vascular bed and receives approximately 20% of total cardiac output 1

• Atrial septostomy decompresses the right heart through right-to-left shunting, though this causes systemic desaturation 2

Why RVADs Are Problematic in Pulmonary Hypertension

Traditional RVADs are actually contraindicated or problematic in the setting of elevated pulmonary vascular resistance:

• RVADs increase pulmonary artery pressure and pulmonary capillary wedge pressure in an RVAD-flow dependent manner, making high-flow support poorly tolerated 1

• Given the intrinsically increased and fixed pulmonary vascular resistance in pulmonary arterial hypertension, RVAD implementation raises theoretical concerns for pulmonary vascular damage 1

• RVAD therapy is not currently routinely performed in pulmonary arterial hypertension, and its utility requires further research 1

Critical Monitoring Requirements

Serial assessment is essential when PA venting is employed:

• Serial echocardiography to assess RV size, function, septal position, and tricuspid regurgitation 2

• Continuous arterial blood pressure monitoring and ECMO flow rates 2

• Avoid thermodilution cardiac output monitoring as it gives erroneous results with ECMO circuits 2

Key Clinical Pitfalls

Volume management and inotrope use require careful consideration:

• Volume overload is particularly dangerous in RV failure; the RV actually prefers euvolemia (CVP 8-12 mmHg), with excessive volume worsening RV distension and tricuspid regurgitation 2

• Inotropes may worsen outcomes, and calcitropic agents can cause progressive RV dysfunction, particularly when systemic vasodilation reduces RV perfusion pressure in the setting of elevated RV pressures 2