The Prognostic Value of Pulmonary Vascular Capacitance Determined by Doppler Echocardiography in Patients with Pulmonary Arterial Hypertension

Objectives: We sought to determine if a novel measurement of pulmonary vascular (PV) capacitance (PVCAP) by Doppler echocardiography predicts all-cause mortality in patients with primary pulmonary arterial (PA) hypertension (PPAH). Background: The prognosis of patients with PPAH is variable and has been difficult to predict using clinical or hemodynamic parameters. PVCAP is a measure of the workload on the right ventricle (RV) and we recently have shown that PVCAP determined by cardiac catheterization is a strong predictor of survival. This same hemodynamic information to calculate PVCAP can be derived from Doppler echocardiography. Therefore, the purpose of this study was to determine if PVCAP from noninvasive Doppler echocardiography would be a useful measure of survival in patients with PPAH. Methods: We analyzed clinical and hemodynamic variables on all patients with PPAH who had a right heart catheterization and echocardiogram from January to December 1999. Because capacitance is directly proportional to stroke volume and inversely proportional to PA pulse pressure, PVCAP was defined as stroke volume/pulse pressure. PVCAP was derived noninvasively from a comprehensive 2-dimensional and Doppler echocardiogram. Using the peak systolic tricuspid regurgitation velocity and the end-diastolic pulmonary regurgitation velocity, the modified Bernoulli equation was used to calculate the PA systolic and diastolic pressures, respectively. Stroke volume was obtained using the volumetric flow through the left ventricular outflow tract. PVCAP was then analyzed as a predictor of mortality, adjusting for other known modifiers of risk. Results: In all, 54 patients (13 men) were studied with a mean age of 44 ± 11 years, ejection fraction of 62 ± 11%, and RV systolic pressure of 90 ± 21 mm Hg. In all, 24% were in World Health Organization (WHO) class II, 52% in class III, and 24% in class IV. During follow-up of 1498 ± 108 days, 12 patients died. The strongest noninvasive predictor of mortality was PVCAP (risk ratio 3.0/mL/mm Hg decrease in PVCAP, 95% confidence interval 1.2-8.0, P = .0212). WHO class, RV index of myocardial performance, RV systolic pressure, and RV ejection time were weaker predictors. PVCAP was also a stronger predictor of mortality than invasively determined PV resistance, right atrial pressure, and mean PA pressure. In multivariate analysis, PVCAP was the only noninvasive predictor of mortality. In quartile analysis the lowest PVCAP quartile had a 4-year mortality of 39% whereas the highest PVCAP had a mortality of 7%. Conclusion: The novel measure of PVCAP, as determined by Doppler echocardiography, is a strong noninvasive predictor of mortality in patients with PPAH and adds prognostic value to conventional risk markers.