PVR Threshold for Mortality Risk Lower Than Previously Thought, Study Suggests

High pulmonary vascular resistance (PVR) is associated with worse mortality rates among people with pulmonary hypertension (PH), and the bottom threshold for what constitutes “elevated” PVR is lower than previously thought, a new study suggests.

“The findings of this study cast the clinical profile of patients who have PH and are at risk for major clinical events into a new and wider light,” Bradley Maron, MD, study co-author and physician at Brigham and Women’s Hospital, said in a press release.

“We can use this information to raise awareness among clinicians on those patients that may need reconsideration for risk factor modification, conventional treatment, and potential clinical trial enrollment,” Maron added.

The study reporting the findings, titled “Pulmonary vascular resistance and clinical outcomes in patients with pulmonary hypertension: a retrospective cohort study,” was published in the journal The Lancet Respiratory Medicine.

PVR is a measurement of how much resistance against blood flow there is in the blood vessels that go from the heart to the lungs. In people with PH, PVR is a useful prognostic indicator — high PVR is generally associated with worse outcomes.

“However, the spectrum of PVR risk in pulmonary hypertension is not known,” the researchers wrote.

“To address this area of uncertainty, we aimed to analyse the relationship between PVR and adverse clinical outcomes in pulmonary hypertension,” they wrote.

The team, from Brigham and Women’s Hospital in Boston, analyzed data from the Veterans Association (VA) national database. In total, clinical data were evaluated from 32,725 people who underwent right heart catheterization and were found to be at risk of PH. That risk was evidenced by a mean pulmonary artery pressure (mPAP) of at least 19 mm Hg.

Statistical models determined that, in this group, the risk of all-cause mortality was significantly increased in people with a PVR of 2.2 Wood units or higher — a 1.71 times higher risk. Of note, a Woods unit is a standard unit of measurement for PVR. Notably, the study’s cutoff value of 2.2 Wood units is lower than the threshold usually used in clinical practice, which is around 3 units.

The risk of hospitalization due to heart failure also was significantly increased in these patients — a 1.27 times higher risk — compared with those with a PVR of less than 2.2 Wood units.

However, using a large national database like that of VA comes with inherent limitations. In particular, the VA only covers veterans, and the sample analyzed was almost entirely male.

As such, the researchers repeated the analysis using data from Vanderbilt University Medical Center in Tennessee. This included data for 2,870 people (49.4% male) with an mPAP of at least 19 mm Hg. In this group, a PVR of 2.2 Wood units or more also was found to be significantly associated with an increase in all-cause mortality. That’s a 1.81 times higher risk.

Based on the results, the team suggested that the new, lower PVR threshold of 2.2 Wood unites expands the range of patients who are considered to have PH and may potentially be at risk for death or hospitalization.

“Pulmonary hypertension is often overlooked in clinical practice, but this study provides a specific context for clinicians and health care workers to understand the range of risk for a large group of patients,” Maron said.

“We have established an evidence-based way to recognize patients with PH who would have otherwise been considered to be normal, but, in fact, have a concerning profile,” he added.

The team is now planning to analyze patient populations not included in this study, such as patients with less common forms of PH or with PH but without heart and lung disease.

“Testing the generalisability of these findings in at-risk populations with fewer cardiopulmonary comorbidities is warranted,” the researchers wrote.