How low should we go? Potential benefits and ramifications of the pulmonary hypertension hemodynamic definitions proposed by the 6th World Symposium

Abstract

Purpose of review: The 6th World Symposium on Pulmonary Hypertension (WSPH) proposed lowering the mean pulmonary artery pressure (mPAP) threshold that defines pulmonary hypertension from ≥ 25 to > 20 mmHg. The historical context and evolution of the pulmonary hypertension definition and the data used to rationalize recent changes are reviewed here.

Recent findings: There are accumulating data on the clinical significance of mildly elevated mPAPs (21-24 mmHg). Studies have demonstrated lower exercise capacity and an increased risk of progression to overt pulmonary hypertension (mPAP ≥ 25 mmHg) in specific at-risk patient populations. Further, large registries across diverse pulmonary hypertension populations have identified increased mortality in patients with mPAPs 21-24 mmHg. Although the clinical sequelae of lowering the mPAP threshold remain unclear, this uncertainty has fueled recent debates within the pulmonary hypertension community.

Summary: The changes to the pulmonary hypertension definition proposed by the 6th WSPH are supported by normative hemodynamic data in healthy individuals as well as studies demonstrating an association between mPAPs above this normal range and increased mortality. Whether the higher mortality observed in patients with mildly elevated mPAPs is directly attributable to pulmonary vascular disease that is amenable to therapeutic intervention remains to be determined.

Figure 1.. Changes over time to the hemodynamic definition of pulmonary hypertension.

Since the 1^st World Symposium on Pulmonary Hypertension (WSPH) in 1973, there have been a number of changes to the hemodynamic criteria for diagnosing PH and pre-capillary PH.

Figure 2.. Effect of different mean pulmonary artery pressure thresholds on the proportion of cardiac output and pulmonary artery wedge pressure combinations leading to an elevated pulmonary vascular resistance.

Combinations of cardiac output (CO) and pulmonary artery wedge pressure (PAWP) resulting in a pulmonary vascular resistance (PVR) ≥3 Woods units (WU) are displayed in dark blue and those resulting in a PVR <3 WU are displayed in light blue.