Background
In pulmonary hypertension subgroups, elevated pulmonary vascular resistance (PVR)
of 3·0 Wood units or more is associated with poor prognosis. However, the spectrum
of PVR risk in pulmonary hypertension is not known. To address this area of uncertainty,
we aimed to analyse the relationship between PVR and adverse clinical outcomes in
pulmonary hypertension.
Methods
We did a retrospective cohort study of all patients undergoing right heart catheterisation
(RHC) in the US Veterans Affairs health-care system (Oct 1, 2007–Sep 30, 2016). Patients
were included in the analyses if data from a complete RHC and at least 1 year of follow-up
were available. Both inpatients and outpatients were included, but individuals with
missing mean pulmonary artery pressure (mPAP), pulmonary artery wedge pressure, or
cardiac output were excluded. The primary outcome measure was time to all-cause mortality
assessed by the Veteran Affairs vital status file. Cox proportional hazards models
were used to assess the association between PVR and outcomes, and the mortality hazard
ratio was validated in a RHC cohort from Vanderbilt University Medical Center (Sept
24, 1998–June 1, 2016).
Findings
The primary cohort (N=40 082; 38 751 [96·7%] male; median age 66·5 years [IQR 61·1–73·5];
median follow-up 1153 days [IQR 570–1971]), included patients with a history of heart
failure (23 201 [57·9%]) and chronic obstructive pulmonary disease (13 348 [33·3%]).
We focused on patients at risk for pulmonary hypertension based on a mPAP of at least
19 mm Hg (32 725 [81·6%] of 40 082). When modelled as a continuous variable, the all-cause
mortality hazard for PVR was increased at around 2·2 Wood units compared with PVR
of 1·0 Wood unit. Among patients with a mPAP of at least 19 mm Hg and pulmonary artery
wedge pressure of 15 mm Hg or less, the adjusted hazard ratio (HR) for mortality was
1·71 (95% CI 1·59–1·84; p<0·0001) and for heart failure hospitalisation was 1·27 (1·13–1·43;
p=0·0001), when comparing PVR of 2·2 Wood units or more to less than 2·2 Wood units.
The validation cohort (N=3699, 1860 [50·3%] male, median age 60·4 years [49·5–69·2];
median follow-up 1752 days [IQR 1281–2999]) included 2870 patients [77·6%] with mPAP
of at least 19 mm Hg (1418 [49·4%] male). The adjusted mortality HR for patients in
the mPAP of 19 mm Hg or more group and with PVR of 2·2 Wood units or more and pulmonary
artery wedge pressure of 15 mm or less Hg (1221 [42·5%] of 2870) was 1·81 (95% CI
1·33–2·47; p=0·0002).
Interpretation
These data widen the continuum of clinical risk for mortality and heart failure in
patients referred for RHC with elevated pulmonary artery pressure to include PVR of
around 2.2 Wood units and higher. Testing the generalisability of these findings in
at-risk populations with fewer cardiopulmonary comorbidities is warranted.
Funding
None.
