A 52-year-old man presents 4 months after radiofrequency catheter ablation for paroxysmal atrial fibrillation with progressive exertional dyspnea, hemoptysis, and persistent cough. Spirometry shows FVC 65%, FEV1 68%, and the FEV1/FVC ratio marked as **C** is 0.85. DLCO is significantly reduced at 55% predicted. CT pulmonary angiography reveals severe ostial stenosis of the right superior pulmonary vein with downstream parenchymal congestion and interstitial edema. Which of the following best explains why the FEV1/FVC ratio marked **C** remains preserved/elevated despite the restrictive spirometric pattern in this patient?

Question

Accepted Answer

D. Both FEV1 and FVC are proportionally reduced due to decreased lung compliance from venous congestion and fibrosis, preserving their ratio. ## Why option 1 is right

In pulmonary vein stenosis complicating AF ablation, the pathophysiology involves localized pulmonary venous hypertension, interstitial edema, and parenchymal fibrosis in the affected lobe. This renders the congested, edematous, and fibrotic lung tissue non-compliant, producing a **restrictive spirometric pattern**. Critically, both FEV1 and FVC are reduced **proportionally** because the primary defect is loss of lung volume (compliance), not airway obstruction. When both values fall together, their ratio (FEV1/FVC) remains preserved or even elevated (0.85 in this case), which is the hallmark of restriction. This preserved ratio at **C** distinguishes restriction from obstruction and is the key diagnostic clue that points toward pulmonary vein stenosis rather than chronic obstructive airway disease. The significantly reduced DLCO (55%) reflects impaired gas exchange across the thickened alveolar-capillary membrane and shunting through poorly ventilated congested segments, confirming the parenchymal involvement.

## Why each distractor is wrong

- **Option 2**: Airway obstruction would produce a *reduced* FEV1/FVC ratio (typically <0.70), not a preserved or elevated one. Pulmonary edema from venous congestion causes restriction, not obstruction.
- **Option 3**: Pulmonary vein stenosis does not selectively reduce FVC while sparing FEV1. Both parameters decline proportionally because the underlying defect is reduced lung compliance, not selective airway narrowing.
- **Option 4**: There is no clinical or radiological evidence of emphysema in this post-ablation patient. Emphysema would produce airway obstruction with a reduced FEV1/FVC ratio, contradicting the preserved ratio seen here.

**High-Yield:** In restrictive lung disease, FEV1 and FVC fall together → preserved FEV1/FVC ratio (≥0.80); in obstructive disease, FEV1 falls disproportionately → reduced FEV1/FVC ratio (<0.70). Pulmonary vein stenosis causes restriction via fibrosis and edema, not obstruction.

[cite: Harrison's Principles of Internal Medicine, 21st ed., Ch. on Pulmonary Hypertension; pathophysiology of post-ablation pulmonary vein stenosis and spirometric patterns in restrictive lung disease]

Answer

A. The ratio is preserved because the patient has concurrent emphysema that offsets the restrictive defect

Answer

B. The FEV1/FVC ratio is elevated because airway obstruction develops secondary to pulmonary edema

Answer

C. Pulmonary vein stenosis causes selective reduction in FVC while maintaining normal FEV1, thereby increasing the ratio

Explanation

Why option 1 is right

Why each distractor is wrong

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