Pulmonary vascular resistance (PVR) >3 Wood Units (WU) is a criterion of the haemodynamic definition of pulmonary arterial hypertension (PAH). However, this conservative cut-off is not evidence based. Data is lacking on the natural history, response to therapy and survival of patients diagnosed with precapillary pulmonary hypertension with mild elevation of PVR.
Using the Australian and New Zealand Pulmonary Hypertension Registry, we analysed outcomes of this unique group treated with PAH therapy between 2004-2017. Treatment for PAH could be prescribed solely on the basis of mPAP and PAWP in Australia. Thus, we studied patients with mPAP≥25 mmHg, PAWP≤15mmHg but PVR<3WU.
82 patients met the haemodynamic inclusion criteria (mean age 63±11 years; 67 females). Underlying aetiologies included idiopathic disease (n=39), connective tissue disease (n=42) and HIV infection (n=1). At diagnosis, mPAP was 27mmHg (IQR25-30), PAWP 13mmHg (IQR11-14) and PVR 2.2WU (IQR1.9-2.7). Baseline 6MWD was 352m (IQR280-416) and 77% were in NYHA 3 or 4 functional class. All patients were commenced on monotherapy with an endothelin receptor antagonist (n=66) or phosphodiesterase-5 inhibitor (n=16). At first re-evaluation (median 5 months; IQR4-12), 6MWD increased by 46m (IQR7-96) and 35% demonstrated improvement in NYHA functional class. After a median follow-up of 65 months (IQR32-101), 18/82 (22.0%) had died, with estimated 1-yr and 5-yr survivals of 98% and 84%, respectively. Death attributed to PAH occurred in 6/18 (33.3%) of these patients. Patients with precapillary PH and “borderline” PVR have adverse outcomes. Such patients appear to respond to PAH therapy but this requires further study in randomised trials.