Prognostic Value of Main Pulmonary Artery Diameter in Pulmonary Arterial Hypertension.

Background: Accurate risk stratification is critical aspect of pulmonary arterial hypertension (PAH) management. It is unclear whether main pulmonary artery (MPA) enlargement offers additional prognostic value to validated risk scores.

Research question: Is MPA diameter prognostic in PAH, independent of the existing risk scores.

Study design and methods: A retrospective review of PAH patients from two large referral centres was conducted. Baseline REVEAL 2.0, REVEAL Lite 2 and ESC/ERS scores were calculated. The primary endpoint was composite death, lung transplantation and right heart failure hospitalisation. Cox proportional hazards models were used for time-to-event analyses. Receiver-operator characteristic and net reclassification improvement analyses additionally assessed the prognostic value of MPA diameter.

Results: 351 patients were included. Baseline MPA diameter was 35.3 ± 7.1 mm. MPA grew by 0.4 ± 1.1 mm/year (1.1% baseline diameter). Over mean 4.0 ± 3.4 years follow up, 190 primary events occurred, and MPA diameter was a predictor (HR 1.06 per mm, 95% CI 1.04-1.07, p<0.001). MPA diameter remained an independent predictor after multivariable adjustments for the three risk scores, and their individual components. MPA growth rate also predicted the outcome (HR 1.79 per mm/year, 95% CI 1.52-2.11, p<0.001), independent of baseline MPA diameter. Area under the receiver-operator characteristic curve for the risk of the primary endpoint at one year was similar for MPA alone (0.72) compared to the three risk scores (0.72-0.75). Furthermore, using MPA in addition to REVEAL 2.0 resulted in risk reclassification in 23% of patients, mostly due to appropriate risk downgrading.

Interpretation: MPA diameter is a significant independent predictor of adverse clinical events in PAH patients without congenital heart disease. It may potentially be a novel prognostic marker in addition to the existing risk scores.