Research in context
Evidence before this study
We searched Medline using PubMed for all full text publications published from database inception to April 10, 2020, using the medical subject heading terms “pulmonary vascular resistance” and “pulmonary hypertension” and “mortality”, as well as the term “catheterisation” in any search field. We included studies in humans aged 19 years or older of the following types: clinical study, dataset, journal article, multicentre study, and observational study. Reviews, biographies, case reports, clinical trials, and non-academic article types or publications not in English were excluded. This search returned 38 publications; of these, two were determined to be case reports and 35 included highly selected clinical populations, such as patients with congenital heart disease, previous pneumothorax, or post-orthotopic heart transplant status. All of these reports included fewer than 320 patients and none included patients with mildly elevated pulmonary artery pressure using the revised haemodynamic definition of pulmonary hypertension. The remaining publication was a single-centre study of 4343 patients, and pulmonary vascular resistance (PVR) emerged from a multivariate analysis as a risk factor for mortality in patients that included (but was not exclusive of) mild pulmonary hypertension. In that study, the continuum of clinical risk associated with PVR was not reported. Overall, knowledge on the clinical significance of PVR in pulmonary hypertension has emphasised historical consensus opinion and data from small studies in selected populations analysing outcome differences using predefined definitions.
Added value of this study
To our knowledge, this study provides the first evidence-based assessment on the continuum of clinical risk associated with PVR in pulmonary hypertension, which is derived from a sufficiently powered national database of patients undergoing right heart catheterisation and validated in a second large patient cohort. This study also uses mortality and heart failure hospitalisation, which are disease-relevant outcomes, to determine the association between PVR and clinical risk using the revised pulmonary artery pressure criterion for pulmonary hypertension.
Implications of all the available evidence
Data from this study show that risk for adverse outcome associated with PVR in pulmonary hypertension emerges at around 2·2 Wood units, which is well below the PVR associated with the disease state in clinical practice. We identified patients with precapillary pulmonary hypertension at the time of right heart catheterisation as particularly vulnerable. Overall, these results suggest that reconsidering the haemodynamic parameters that define pulmonary hypertension in patients with cardiopulmonary disease is warranted, and they identify a need for early detection strategies to capture this large and vulnerable population.