Histological Analysis of Lung Tissue and Pulmonary Vessels in Cardiac Surgery Patients with Mitral Valve Disease and Pulmonary Hypertension

Aim        To study morphological features of lung tissue and pulmonary vessels in patients with pulmonary hypertension (PH) associated with acquired mitral valve (MV) defects, with indications for surgical treatment.

Material and methods          This cross-sectional study included 105 patients with acquired MV defect of non-infectious origin (median age 60.0 [51.0; 66.0] years, 55.24% men) who underwent corrective surgery under cardiopulmonary bypass between 2024 through March 2025. PH was verified by right heart catheterization before defect correction. In 26 patients with MV defect and PH and 12 patients without PH, intraoperative lung tissue puncture biopsy samples were collected to assess changes in the lung parenchyma and microvasculature.

Results    In patients with MV defect and PH, the condition of arterioles was characterized by a larger area of intimal hyperplasia and predominantly the presence of thrombosis (34.6%). In patients with MV defect without PH, partial thrombosis of arterioles was more often found (41.66%), and plethoric arterioles were observed in 41.66%. During morphometry of pulmonary vessels, it was noted that the a calculated systolic pressure in the pulmonary artery of >38 mm Hg according to preoperative echocardiography (EchoCG) had a moderate inverse correlation with the area of the vascular wall (Kendall's rank correlation coefficient tau (τ) = -0.34; p=0.01) and a moderate direct association with the greatest thickness at the site of arteriolar intimal hyperplasia (τ = 0.39; p = 0.04). A moderate inverse correlation was found between the systolic excursion of the tricuspid valve annulus (1.7 cm or more) and the greatest thickness at the site of arteriolar intimal hyperplasia (τ= –0.47; p=0.04). MV stenosis was associated with the presence of thrombosed capillaries (odds ratio (OR) 8.75; 95% confidence interval (CI) 1.1-69.5; p=0.029) and focal interstitial fibrosis (OR 10.66; 95% CI 0.89-126.78; p=0.046). The presence of mitral stenosis had a moderate correlation with perivascular fibrosis (τ=0.41; p=0.005). A body mass index of >25 kg/m² was associated with reduced odds of arteriolar media thickening (OR 0.15; 95% CI 0.02-1.01; p=0.03).

Conclusion            The severity of PH and right ventricular dysfunction, as determined by EchoCG before MV defect correction, may reflect morphometric changes in the pulmonary vessels. The nature of MV lesion, based on its stenosis type, is associated with a more than 8-fold increase in the odds of thrombosed capillaries and a 10-fold increase in the odds of focal interstitial fibrosis. Being overweight or obese was associated with an 85% reduction in the odds of arteriolar media thickening, as determined by pulmonary vascular morphometry.

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