Phenotyping of patients with mild pulmonary hypertension.

Revised haemodynamic criteria for pulmonary hypertension (PH)-mean pulmonary artery pressure (mPAP) >20 mm Hg and pulmonary vascular resistance (PVR) >2 Wood Units (WU)-have defined new subsets of patients with mild PH. We aimed to characterise their clinical profile and prognosis. We included consecutive incident, treatment-naïve patients undergoing right heart catheterisation at a PH referral centre. Patients with mPAP 21-24 mm Hg and pulmonary artery wedge pressure (PAWP) ≤15 mm Hg were stratified by PVR values to identify those with unclassified PH (PVR≤2 WU) and mild precapillary PH (PVR>2 WU). Patients with mild precapillary PH were compared with matched controls with normal haemodynamics and with patients meeting previous pulmonary arterial hypertension (PAH) haemodynamic criteria (mPAP≥25 mm Hg, PAWP≤15 mm Hg, PVR>3 WU). Among 259 patients with mPAP 21-24 mm Hg and PAWP≤15 mm Hg, 76% had left heart or lung disease. In unclassified PH, mPAP elevation was mainly due to high stroke volume index (SVI) or backward transmission from borderline PAWP. In mild precapillary PH, SVI was the only independent haemodynamic predictor of survival. Survival was similar between mild precapillary PH and PAH patients. A limited number of patients with PAH risk factors progressed to overt PAH and, in the absence of comorbidities, appeared to benefit from PAH therapies. Unclassified PH is mainly related to pulmonary overflow or backward transmission from borderline PAWP. Mild precapillary PH is typically associated with comorbidities and not necessarily an early PAH stage. SVI is a key prognostic marker. Careful clinical phenotyping is essential to identify the small subset who may benefit from targeted therapies.