Abstract 5928: Use of Echo Assessment of Raised Pulmonary Vascular Resistance in Follow-up
Background: Pulmonary vascular resistance (PVR) is important for monitoring response to therapy and assessing prognosis in pulmonary hypertension (PAH). PVR can be obtained using the equation PVR = (TRV × 10/TVIRVOT) + 0.16 (where TRV is tricuspid regurgitation velocity and TVIRVOT is RV outflow time-velocity integral; Abbas, JACC 2003) but this was validated against invasive measures in only 44 pts. We sought the correlation of echo and invasive PVR at levels required for diagnosis (1.8 Wood units) and levels that are usual for follow-up of pts with PAH.
Methods: We compared invasive- and echo-PVR in 72 patients with PAH undergoing right heart catheterisation. Echo right ventricular systolic pressure (RVSP) was calculated using the modified Bernoulli equation from the TRV. Other echo data included estimated RA pressure, RV function (tissue Doppler RV-S′) and E/E′. Invasive-PVR was calculated by the equation: PVRi = MPAP-PCWP/cardiac output. We also compared sequential invasive- and echo-PVR in 11 pts with established pulmonary hypertension who underwent serial catheterisation and the difference was sought at various levels of PVR using Bland-Altman analysis. A general linear model was used to identify potential causes of discordance.
Results: PVRe >1.8 had high sensitivity (96%) in 50 pts with PVRi >1.8 WU, and good specificity (86%) in 21with normal PVR. There was a good correlation between PVRe and PVRi (r=0.77, p<0.01), but echo underestimated markedly elevated PVR. This underestimation was independently associated with RV-S′ (β=−0.38, 95%CI −0.08 to −0.56, p=0.011) and the difference between echo- and cath-PASP (β=−0.30, 95%CI −0.14 to 0.17, p=0.02), but was unrelated to gender, EF, E/E′ or stroke volume. In 11 patients with follow-up studies, the change between first and latest PVR (−3.9+/− 4.4) was significantly different (+0.18+/− 0.80 (p=0.03)) between two modalities. Echo accurately detected drop in PVR in only 2 out of 8 patients whose cath PVR fell on therapy by at least one standard deviation.
Conclusion: Although echo is effective in distinguishing normal from abnormal PVR, echo underestimates high levels of PVR. This underestimation most likely accounts for reduced ability of echo to detect PVR changes on treatment in patients with PAH.