How to treat a patient with Systemic Arterial Mean (SAM) physiology and Right Ventricular (RV) failure, particularly those with a history of pulmonary hypertension or congenital heart disease?

Managing SAM Physiology with Concurrent RV Failure

In patients with systemic arterial mean (SAM) physiology and RV failure, the critical priority is maintaining systemic vascular resistance (SVR) greater than pulmonary vascular resistance (PVR) to prevent RV ischemia, while simultaneously optimizing RV preload, supporting RV contractility with dobutamine, and reducing RV afterload with pulmonary vasodilators. 1

Fundamental Hemodynamic Principle

The cornerstone of management is ensuring SVR exceeds PVR at all times. 1, 2

• Unlike left ventricular coronary perfusion (diastolic only), RV coronary perfusion occurs during both systole and diastole 1
• When systolic pulmonary arterial pressure exceeds systolic systemic arterial pressure (SPAP > SSAP), RV ischemia results 1
• Target systolic blood pressure goals higher than typical ICU patients 1
• Direct CVP measurement via central line is essential, as non-invasive estimates are unreliable in this population 1, 3

Immediate Hemodynamic Assessment

Obtain invasive monitoring immediately: 1, 3

• Central venous line for direct CVP and mixed venous oxygen saturation 1, 3
• Consider pulmonary arterial catheter for precise PVR/SVR ratio monitoring, though not mandatory if CVP and SvO2 available 1, 3
• Continuous arterial line monitoring 3
• Transthoracic echocardiography to assess RV size, function, septal position, and tricuspid regurgitation 1

Preload Optimization

Volume management requires extreme caution—aggressive volume loading worsens RV function in pressure-overloaded ventricles. 2, 4

• Close RV monitoring during any fluid administration 4
• Elevated preload from volume overload increases RV wall stress, leading to RV dilation and functional tricuspid regurgitation 1
• Diuresis is often necessary for systemic venous congestion, hepatic congestion, and peripheral edema 1
• Thiazides, loop diuretics, and aldosterone antagonists as appropriate 1

Vasopressor Selection to Maintain SVR > PVR

Use low-dose norepinephrine as first-line vasopressor to maintain adequate SVR. 4

• Replacement-dose vasopressin is particularly useful to offset SVR drops, especially in septic or liver disease patients where vasopressin deficiency is common 1, 2, 3
• Maintain mean arterial pressure ≥65 mmHg after adequate fluid resuscitation 2
• Avoid allowing PVR to exceed SVR, which causes RV ischemia 3

Inotropic Support for RV Contractility

Dobutamine is the preferred inotrope for RV failure. 1, 4

• Low-dose dobutamine improves RV function without significantly increasing PVR 1, 4
• Preferred over milrinone due to shorter half-life when hypotension risk exists 1, 3
• Other acceptable inotropes with neutral/beneficial PVR effects: milrinone and epinephrine 1, 3
• Phosphodiesterase type III inhibitors (milrinone) reduce PVR and improve RV function, though hypotension is frequent 4

Pulmonary Vasodilators to Reduce RV Afterload

Acute Management

Inhaled nitric oxide (iNO) is first-line for acute RV afterload reduction. 3, 4

• Acutely decreases PVR and improves cardiac output 1, 3, 4
• Short half-life allows rapid titration 3
• Does not affect SVR (critical advantage) 3
• Upon weaning iNO, start/restart phosphodiesterase-5 inhibitor to prevent rebound pulmonary hypertension 3

Chronic/Subacute Management

Phosphodiesterase-5 inhibitors reduce pulmonary hypertension and support the RV. 1, 3

• Sildenafil causes pulmonary vascular smooth muscle relaxation and lesser degree of systemic vasodilation 5
• Reduces PVR while maintaining favorable SVR/PVR ratio 1, 3
• Alternative agents: tadalafil 3

For severe/refractory cases, consider additional PAH-targeted therapies: 3, 6

• Continuous IV epoprostenol for WHO functional class IV symptoms improves functional class, exercise capacity, and survival 3, 6
• Endothelin receptor antagonists (bosentan, ambrisentan) 3
• Prostacyclin pathway agonists (treprostinil) 3
• Combination therapy with endothelin receptor antagonist plus inhaled prostanoid for patients unable to manage parenteral therapy 3

Respiratory Management

Maintain oxygen saturation >90% to prevent hypoxia-induced PVR increases. 3

• If mechanical ventilation required, use low tidal volume strategy to minimize RV afterload 3
• Keep peak pressures <30 cmH2O 3
• Limit positive end-expiratory pressure to ≤10 cmH2O when possible 3
• Avoid permissive hypercapnia—acidosis acutely increases PVR 3

Mechanical Circulatory Support

For refractory RV failure despite maximal medical therapy, consider ECMO. 1, 3

• Indications: pulmonary hypertensive crisis, low cardiac output, or RV failure unresponsive to medical management 1, 3
• Veno-arterial ECMO can bridge awake end-stage patients to lung transplantation 1
• Additional mechanical support options for LV unloading if needed (intra-aortic balloon pump, Impella) 3

Interventional Strategies for Progressive Disease

For children with severe PH and RV failure, atrial septal defect (ASD) creation/enlargement provides RV volume unloading. 1

• Improves LV preload and cardiac output at expense of decreased systemic oxygen saturation 1
• Provides volume (not pressure) unloading of failing RV 1
• Transcatheter approach preferred (balloon atrial septostomy, static balloon dilation, atrial flow regulator device, stent) 1
• Consider for markedly elevated right atrial pressure or recurrent syncope despite optimized medical management 1

Transplantation Considerations

Refer for transplant evaluation after inadequate response to initial monotherapy; list after inadequate response to maximal combination therapy. 1

• Bilateral lung transplantation is preferred surgical approach for PH 1
• Heart-lung transplantation considered for unrecoverable RV systolic dysfunction or significant LV diastolic dysfunction 1
• Combined heart-lung transplant may be necessary for massive RV enlargement or uncorrectable congenital heart disease with coexisting LV dysfunction 1
• Five-year survival post-transplant: 52-75%; ten-year survival: 45-66% 1

Critical Pitfalls to Avoid

• Never allow aggressive volume expansion in RV failure—worsens RV function 2, 3, 4
• Never permit PVR to exceed SVR—causes RV ischemia 1, 2, 3
• Never use static CVP values alone for fluid therapy decisions 3
• Never use permissive hypercapnia—acidosis increases PVR 3
• High LVAD speeds can increase venous return to failing RV, worsening RV failure 1
• Underfilled LV causes septal shift, removing septal contribution to RV contractility 1

Special Considerations for Systemic RV Physiology

Medical therapy evidence for systemic RVs (congenitally corrected transposition, d-TGA with Mustard/Senning) is limited. 1

• ACE inhibitors, ARBs, and aldosterone antagonists show no conclusive benefit for systemic RV dysfunction 1
• Beta-blocker data insufficient; await results of ongoing trials 1
• Focus remains on afterload reduction, neurohormonal optimization, and symptom management 1
• These patients frequently develop PAH requiring evaluation for heart-lung vs. heart-only transplantation 7