Right heart failure as a cause of pulmonary congestion in pulmonary arterial hypertension

Aims: Recent studies have shown that lung ultrasound-assessed pulmonary congestion is worse in heart failure when pulmonary vascular resistance (PVR) is increased, suggesting a paradoxical relationship between right heart failure and increased lung water content. Accordingly, we wondered if lung ultrasound would reveal otherwise clinically silent pulmonary congestion in patients with pulmonary arterial hypertension (PAH). Methods and results: All patients referred for suspicion of PAH in a tertiary centre from January 2020 to December 2022 underwent a complete diagnostic work-up including echocardiography, lung ultrasound and right heart catheterization. Pulmonary congestion was identified by lung ultrasound B-lines using an 8-site scan. The study enrolled 102 patients with idiopathic PAH (mean age 53 ± 13 years; 71% female). World Health Organization functional classes I, II, and III were found in 2%, 52%, and 46% of them, respectively. N-terminal pro-brain natriuretic peptide (NT-proBNP) was 377 pg/ml (interquartile range [IQR] 218–906). B-lines were identified in 77 out of 102 patients (75%), with a median of 3 [IQR 1–5]. At univariable analysis, B-lines were positively correlated with male sex, age, NT-proBNP, systolic pulmonary artery pressure (sPAP), right atrial pressure (RAP), PVR, left ventricular end-diastolic volume and tricuspid annular plane systolic excursion (TAPSE), and negatively with cardiac output and stroke volume. At multivariable analysis, RAP (p < 0.001), TAPSE/sPAP (p = 0.001), and NT-proBNP (p = 0.04) were independent predictors of B-lines. Conclusion: Lung ultrasound commonly discloses pulmonary congestion in PAH. This finding is related to right ventricular to pulmonary artery uncoupling, and may tentatively be explained by increased central venous pressure impeding lymphatic outflow.