Echocardiographic assessment of raised pulmonary vascular resistance: application to diagnosis and follow-up of pulmonary hypertension

Objective To optimise an echocardiographic estimation of pulmonary vascular resistance (PVR_e) for diagnosis and follow-up of pulmonary hypertension (PHT).
Design Cross-sectional study.
Setting Tertiary referral centre.
Patients Patients undergoing right heart catheterisation and echocardiography for assessment of suspected PHT.
Methods PVR_e ([tricuspid regurgitation velocity X10/ (right ventricular outflow tract velocity-time integral +0.16) and invasive PVR_i ((mean pulmonary artery systolic pressure-wedge pressure)/cardiac output) were compared in 72 patients. Other echo data included right ventricular systolic pressure (RVSP), estimated right atrial pressure, and E/e' ratio. Difference between PVR_e and PVR_i at various levels of PVR was sought using Blande-Altman analysis. Corrected PVR_c ((RVSP-E/e')/ RVOT_VTI) (RVOT, RV outflow time; VTI, velocity time integral) was developed in the training group and tested in a separate validation group of 42 patients with established PHT.
Results PVR_e>2.0 had high sensitivity (93%) and specificity (91%) for recognition of PVR_i>2.0, and PVR_c provided similar sensitivities and specificities. PVR_e and PVR_i correlated well (r=0.77, p<0.01), but PVR_e underestimated marked elevation of PVR_i-a trend avoided by PVR_c. PVR_c and PVR_e were tested against PVR_i in a separate validation group (n=42). The mean difference between PVR_e and PVR_i exceeded that between PVR_c and PVR_i (2.8+-2.7 vs 0.8+-3.0 Wood units; p<0.001). A drop in PVR_i by at least one SD occurred in 10 patients over 6 months; this was detected in one patient by PVR_e and eight patients by PVR_c (p=0.002).
Conclusion PVR_e distinguishes normal from abnormal PVR_i but underestimates high PVR_i. PVR_c identifies the severity of PHT and may be used to assess treatment response.