Can a small atrial shunt (atrial septal defect) cause pulmonary hypertension in patients with a history of congenital heart disease or previous cardiac surgeries?

Can Small Atrial Shunts Cause Pulmonary Hypertension?

Yes, small atrial septal defects can cause pulmonary hypertension, though the clinical picture resembles idiopathic PAH rather than typical shunt-related disease. 1

Definition of Small Atrial Shunts

According to the ESC/ERS guidelines, small atrial septal defects are defined as those ≤2.0 cm in effective diameter as assessed by echocardiography in adult patients. 1 These defects are classified separately from moderate-to-large defects because they behave differently in terms of hemodynamics and pulmonary vascular disease development.

Mechanism and Clinical Presentation

In small defects, the shunt itself does not account for the development of elevated pulmonary vascular resistance. 1 The ESC/ERS guidelines specifically state that patients with small defects (ASD <2 cm) who develop PAH present with:

• Marked elevation in pulmonary vascular resistance despite the small defect size 1
• Clinical picture very similar to idiopathic PAH rather than typical shunt-related disease 1
• Closing the defects is contraindicated in these patients 1

This is fundamentally different from larger defects where persistent exposure of the pulmonary vasculature to increased blood flow and pressure directly causes pulmonary obstructive arteriopathy. 1

Evidence from Clinical Studies

Real-world data confirms this phenomenon occurs in practice:

• In a Portuguese cohort of 181 consecutive ASD patients, some patients with central ASDs <5 mm diameter still developed pulmonary hypertension, demonstrating that even very small defects can be associated with PAH. 2
• The prevalence of PAH in adults with ASD ranges from 8-10%, and this includes patients across the spectrum of defect sizes. 3
• Patients with smaller and simpler defects who develop PH tend to be older at presentation, suggesting a different pathophysiological mechanism than flow-related injury. 2

Critical Diagnostic Distinction

The key clinical question is whether the small defect is causing the PAH or is merely coincidental. 1 The ESC/ERS guidelines classify this as "PAH with small/coincidental defects" to emphasize that:

• The defect size and hemodynamics (Qp/Qs ratio, pressure gradient) do not explain the severity of pulmonary vascular disease 1
• These patients should be managed as idiopathic PAH rather than CHD-associated PAH 1
• Defect closure will not improve and may worsen outcomes 1

Management Implications

For small ASDs with PAH, the treatment approach follows idiopathic PAH protocols, not shunt closure. 1 The guidelines are explicit that:

• Patients require hemodynamic evaluation with right heart catheterization to assess pulmonary vascular resistance (PVR >3 Wood units confirms PAH) 1
• PAH-specific therapies (endothelin receptor antagonists, phosphodiesterase-5 inhibitors, prostanoids) should be initiated 1
• Surgical or percutaneous closure is contraindicated when marked PVR elevation exists with a small defect 1

Common Pitfall to Avoid

The critical error is assuming all ASDs with PAH should be closed. 3 In patients with small defects and severe PAH, closure can be harmful because:

• The defect may serve as a "pop-off" valve allowing right-to-left shunting during episodes of elevated right heart pressure 3
• Closure eliminates this safety mechanism without addressing the underlying pulmonary vascular disease 3
• Adults with progressive pulmonary vascular disease may have worse outcomes after shunt closure than patients managed medically 3

The hemodynamic data must be interpreted in the context of defect anatomy—a small defect with disproportionately elevated PVR indicates the defect is not the primary cause of PAH. 3