Can Pulmonary Hypertension with ASD Cause Right-to-Left Shunt?
Yes, a patient with pulmonary hypertension and an ASD can absolutely develop a right-to-left shunt when right atrial pressure exceeds left atrial pressure, which occurs in severe pulmonary hypertension and represents Eisenmenger physiology. 1
Mechanism of Shunt Reversal
Right-to-left shunting occurs when right atrial pressure exceeds left atrial pressure, which happens in the setting of severe pulmonary hypertension, subpulmonary chamber outflow obstruction, or abnormalities of right ventricular compliance 1
The natural history of unclosed ASDs typically involves initial left-to-right shunting that causes pulmonary overcirculation and progressive pulmonary vascular disease 1
As pulmonary vascular resistance increases and approaches or exceeds systemic vascular resistance, the pressure gradient reverses, causing deoxygenated blood to shunt from right to left 1
Clinical Significance and Contraindications to Closure
ASD closure is absolutely contraindicated when severe irreversible pulmonary hypertension with right-to-left shunting has developed 2:
Closure should not be performed when PA systolic pressure is greater than two-thirds systemic pressure 2
Closure should not be performed when pulmonary vascular resistance is greater than two-thirds systemic vascular resistance 2
Closure should not be performed when a net right-to-left shunt is present 2
Patients with severe irreversible PAH and no evidence of left-to-right shunt should not undergo ASD closure 2
Clinical Manifestations
The development of right-to-left shunting produces distinct clinical features:
Hypoxemia that is unresponsive to supplemental oxygen because the shunt bypasses the pulmonary circulation 1
Risk of paradoxical embolism where venous thrombi can bypass pulmonary filtration and enter systemic circulation 1
Cyanosis and clubbing in advanced cases
Diagnostic Approach
Measurement of oxygen saturation should be performed in feet and both hands to assess for right-to-left shunting 2
Saline contrast echocardiography is more sensitive than Doppler for detection of low-velocity right-to-left shunts 1
Cardiac catheterization is useful when pulmonary hypertension is suspected to accurately measure pulmonary artery pressures and calculate pulmonary vascular resistance 2
Emerging Treatment Considerations
While traditionally considered inoperable, recent evidence suggests selected patients may benefit from aggressive therapy:
Pretreatment with pulmonary arterial hypertension therapies (prostaglandins, endothelin blockers, PDE-5 inhibitors) with demonstrated reduction in pulmonary arterial resistance of >20% portends favorable prognosis after ASD closure 2
Case reports demonstrate successful closure after prolonged vasodilator therapy in patients previously considered to have "irreversible" pulmonary arteriopathy 3, 4, 5, 6
Patients with anatomically large defects (>25 mm) and large left-to-right shunts at baseline with high probability of reversible pulmonary vascular resistance may benefit from fenestrated device closure despite elevated pressures 4
Critical Pitfall
The presence of right-to-left shunting indicates Eisenmenger physiology and represents an absolute contraindication to ASD closure in most cases, as closure would eliminate the "pop-off" mechanism that allows the failing right ventricle to decompress, potentially causing acute right heart failure and death 2. Collaboration between adult congenital heart disease specialists and pulmonary hypertension experts is essential for these complex patients 2.