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BACKGROUND
The ratio of tricuspid regurgitation velocity (TRV) to the time-velocity integral of the right ventricular outflow tract (TVIRVOT) has been studied as a reliable measure to distinguish elevated from normal pulmonary vascular resistance (PVR). The equation TRV/TVIRVOT × 10 + 0.16 (PVRecho) has been shown to provide a good noninvasive estimate of PVR. However, its role in patients with significantly elevated PVR (> 6 Wood units [WU]) has not been conclusively evaluated. The aim of this study was to establish the validity of the TRV/TVIRVOT ratio as a correlate of PVR. The role of TRV/TVIRVOT was also compared with that of a new ratio, TRV(2)/TVIRVOT, in patients with markedly elevated PVR (>6 WU).

METHODS
Data from five validation studies using TRV/TVIRVOT as an estimate of PVR were compared with invasive PVR measurements (PVRcath). Multiple linear regression analyses were generated between PVRcath and both TRV/TVIRVOT and TRV(2)/TVIRVOT. Both PVRecho and a new derived regression equation based on TRV(2)/TVIRVOT: 5.19 × TRV(2)/TVIRVOT - 0.4 (PVRecho2) were compared with PVRcath using Bland-Altman analysis. Logistic models were generated, and cutoff values for both TRV/TVIRVOT and TRV(2)/TVIRVOT were obtained to predict PVR > 6 WU.

RESULTS
One hundred fifty patients remained in the final analysis. Linear regression analysis between PVRcath and TRV/TVIRVOT revealed a good correlation (r = 0.76, P < .0001, Z = 0.92). There was a better correlation between PVRcath and TRV(2)/TVIRVOT (r = 0.79, P < .0001, Z = -0.01) in the entire cohort as well as in patients with PVR > 6 WU. Moreover, PVRecho2 compared better with PVRcath than PVRecho using Bland-Altman analysis in the entire cohort and in patients with PVR > 6 WU. TRV(2)/TVIRVOT and TRV/TVIRVOT both predicted PVR > 6 WU with good sensitivity and specificity.

CONCLUSIONS
TRV/TVIRVOT is a reliable method to identify patients with elevated PVR. In patients with TRV/TVIRVOT > 0.275, PVR is likely > 6 WU, and PVRecho2 derived from TRV(2)/TVIRVOT provides an improved noninvasive estimate of PVR compared with PVRecho.