Right Ventricular Dilatation Without Pulmonary Hypertension: Next Steps
You must evaluate for intracardiac shunts (particularly atrial septal defect or patent foramen ovale) and pulmonary arteriovenous malformations, given the combination of unexplained RV dilatation with normal pulmonary pressures and the patient's history of migraine with aura.
What You Haven't Excluded Yet
Intracardiac Shunts
- Atrial septal defect (ASD) or patent foramen ovale (PFO) remain the most likely undiagnosed causes of isolated RV dilatation with normal PA pressures 1
- These shunts cause volume overload of the right ventricle without necessarily elevating pulmonary artery pressures, particularly in left-to-right shunts 1
- The migraine with aura history is particularly relevant here, as right-to-left shunts are strongly associated with migraine with aura 2, 3
Pulmonary Arteriovenous Malformations (PAVMs)
- PAVMs are independently associated with migraine with aura (OR 4.6,95% CI 1.84-11.2) and should be specifically excluded 3
- In patients with migraine with aura, 68% had PAVMs compared to 32% in non-migraine controls 3
- PAVMs can cause right-to-left shunting and may contribute to RV volume changes without pulmonary hypertension 3
Chronic Thromboembolic Disease
- Chronic pulmonary embolism with recanalization can present with RV dilatation and PA enlargement but normal resting pressures on catheterization 4, 1
- Look for eccentric thrombus, recanalized thrombus with calcification, abrupt vessel cutoffs, thin linear webs, and mosaic attenuation on CT 1
Recommended Next Steps
Immediate Diagnostic Workup
1. Transthoracic Echocardiography with Agitated Saline (Bubble Study)
- This is the critical next test to detect intracardiac shunts 1
- Perform with Valsalva maneuver to unmask PFO 1
- Quantify shunt severity and measure pulmonary-to-systemic flow ratio (Qp:Qs) 1
2. High-Resolution Chest CT or CT Pulmonary Angiography
- Specifically evaluate for PAVMs, looking for feeding arteries and draining veins 1, 3
- Reassess for chronic thromboembolic changes: eccentric thrombus, webs, vessel cutoffs, mosaic perfusion 1
- Evaluate for interstitial lung disease or emphysema that might have been missed 4
3. Cardiac MRI
- MRI is the gold standard for RV function and can quantify intracardiac shunts by measuring pulmonary-to-systemic flow ratios with sensitivity 93-100% and specificity 87-100% 1
- Provides accurate RV volumes, mass, and function assessment 1
- Can detect extracardiac shunts and anomalous pulmonary venous return 1
Additional Considerations
Transesophageal Echocardiography (TEE)
- Consider if transthoracic bubble study is equivocal or to better characterize ASD anatomy before potential closure 1
Pulmonary Function Tests Review
- Ensure DLCO was measured; a low DLCO (<45% predicted) with normal spirometry could suggest PVOD or PAVMs 4
- Combined emphysema and fibrosis can pseudonormalize spirometry while DLCO remains reduced 4
Clinical Pitfalls to Avoid
- Don't assume normal PA pressures exclude all causes of RV dilatation—volume overload from shunts is a distinct pathophysiology 1
- The migraine with aura history is not coincidental—it significantly increases the likelihood of right-to-left shunts from either cardiac or pulmonary sources 2, 3, 5, 6
- Standard CT may miss small PAVMs—specifically request evaluation for these lesions given the clinical context 3
- Right heart catheterization at rest may be normal in chronic PE—exercise hemodynamics or V/Q scanning may be needed if suspicion remains high 4
Why This Matters
The combination of RV dilatation (RV/LV ratio 1.33, significantly elevated) with PA trunk dilatation (PA/Aorta ratio 1.1) but normal pulmonary pressures creates a diagnostic mismatch that demands explanation 1. Volume overload from undetected shunts is the most common cause of this pattern. The patient's migraine with aura substantially increases pre-test probability for both cardiac and pulmonary shunts 2, 3, 6.