Noninvasive Estimation of Pulmonary Vascular Resistance Using Right Ventricular Outflow Doppler Analysis

Abstract

Background: Right heart catheterization (RHC) is the gold standard for measuring pulmonary vascular resistance (PVR). Current noninvasive methods lack accuracy, especially in moderate to severe pulmonary arterial hypertension.

Objectives: The objective of the study was to develop and validate a novel echocardiographic method for estimating PVR using right ventricular outflow tract Doppler notch analysis.

Methods: In this prospective study, of 95 patients undergoing RHC, 35 with isolated postcapillary pulmonary hypertension (PVR <2.0 WU) and no discernible Doppler notches were excluded. Of the remaining, 54 patients with interpretable Dopplers were divided into derivation (n = 30) and validation (n = 24) cohorts, all undergoing invasive PVR (iPVR) measurement and echocardiography within 24 hours. Right ventricular outflow tract Doppler, specifically the ratio of notch time (NT) to ejection time, was analyzed to derive a regression equation for non-invasive PVR (niPVR). The model was validated against iPVR and compared with 5 existing methods.

Results: Stepwise linear regression identified the inverse of NT as the strongest predictor of iPVR. After adjusting for heart rate, the model (R² = 0.93) yielded non-iPVR = 7.1∗(ejection time/NT) - 9.36. Validation against 5 established methods showed superior performance across a PVR range of 2.3 to 14.2 WU, with the highest Pearson correlation (r: 0.76; P < 0.0001; 95% CI: 0.52-0.89). Bland-Altman analysis confirmed superior agreement.

Conclusions: This novel echocardiographic method offers feasible, rapid, reliable PVR estimation with strong correlation to invasive measurements. Although not a substitute for RHC, this promising preliminary finding from a selective cohort may aid in identifying candidates for invasive testing and guide pulmonary hypertension management. Larger, multicenter validation is warranted.

Keywords: Wood units; echocardiography; postcapillary pulmonary hypertension; precapillary; pulmonary impedance.

Graphical abstract

Figure 1

Schematic Illustrating RVOT Doppler Envelope and Technical Tips for Accurate Measurements A) The ratio: ET/NT is the core component of the Doppler Notch regression equation used to estimate niPVR. [niPVR = 7.1 · (Ejection time/Notch time) − 9.36]. (B) Case example of a 65 y/o with type 2 diabetes, COPD, emphysema, diastolic dysfunction, WHO type 3 pulmonary hypertension, and hypoxemic respiratory failure. Right heart cath data: pulmonary Artery (S/D/M): 101/41/65; pulmonary capillary wedge: 22/20/20; right atrium (a/v/M): 28/24/22 mm Hg (mean pressures bolded). Fick Cardiac output: 2.7 L/min. Estimated invasive pulmonary vascular resistance: 16.6 Wood units. See below estimations of niPVR obtained from RVOT Doppler envelopes at different sweep speeds (A and B) in the same patient. AT = acceleration time; COPD = chronic obstructive pulmonary disorder; ET = ejection time; niPVR = noninvasive pulmonary vascular resistance; NT = notch time; PVC = pulmonary valve closure; PVO = pulmonary valve opening; RVOT = right ventricular outflow tract.

Central Illustration

Noninvasive Estimation of Pulmonary Vascular Resistance Using Right Ventricular Outflow Tract Doppler Analysis ET = ejection time; IPVR = invasive estimation of PVR; mPAP = mean pulmonary artery pressure; niPVR = non-invasive estimation of PVR; NT = notch time; PVR = pulmonary vascular resistance; RVOT = right ventricular outflow tract.

Figure 2

Correlation Matrix Heatmap The heatmap displays correlation coefficients between various variables, with values ranging from −1 (negative correlation, red) to 1 (positive correlation, blue). Darker shades represent stronger correlations. Abbreviations as in Figure 1.

Figure 3

Scatter Plots With Regression Lines This figure presents scatter plots of models against iPVR. Each plot includes a regression line. The top panel displays the correlation trends for all models combined. PVR = pulmonary vascular resistance; RHC = right heart catheterization; other abbreviations as in Figure 1.

Figure 4

Bland-Altman Correlation Plots Bland-Altman Correlation plots show levels of agreement between the different models and invasive PVR. A) Doppler Notch Equation (niPVR) vs. iPVR. The paired t-test mean difference is 0.84 with a SD of 2.14 WU and P = 0.068 limit of agreement of 0.84 ± 4.19. Doppler Notch equation: niPVR = 7.1 · (Ejection time/Notch time) − 9.36 (Afonso et al); B) Model 1 vs. iPVR. The paired t-test mean difference is 3.05 with a SD of 3.24 WU and P = 0.0001 and limit of agreement of 3.05 ± 6.35. Model 1: PVR = 10 × Peak TR velocity/RVOT VTI + 0.16; Abbas et al; C) Model 2 vs. iPVR. The paired t-test mean difference is (-) 1.71 with a SD of 3.28 WU and P = 0.018 and limit of agreement of (-) 1.71 ± 6.43. Model 2: PVR = PASP/RVOT VTI + 3, Opotowsky et al; D) Model 3 vs. iPVR. The paired t-test mean difference is (-) 3.70 with a SD of 3.82 WU and P < 0.0001 and limit of agreement of (-) 3.70 ± 7.49. Model 3: PVR = 2.34 + TR PG/RVOT VTI × 1.48, Kouzu et al; E) Model 4 vs. iPVR. The paired t-test mean difference is 0.05 with a SD of 3.56 WU and P = 0.949 and limit of agreement of 0.05 ± 7.00. Model 4: PVR = 5.19 × (TRV2 /RVOT VTI) − 0. 4, Abbas et al; and F) Model 5 vs. iPVR. The paired t-test mean difference is (-) 0.75 with a SD of 3.96 WU and P = 0.360 and limit of agreement of (-) 0.75 ± 7.76. pulmonary vascular resistance index = 1.97 + 190.71 (systolic pulmonary artery pressure/[HR × RVOT VTI]), Haddad et al; for model 5, the estimated pulmonary vascular resistance index was divided by BSA to obtain PVR. Abbreviation as Figures 1 and 3.

Figure 4

Bland-Altman Correlation Plots Bland-Altman Correlation plots show levels of agreement between the different models and invasive PVR. A) Doppler Notch Equation (niPVR) vs. iPVR. The paired t-test mean difference is 0.84 with a SD of 2.14 WU and P = 0.068 limit of agreement of 0.84 ± 4.19. Doppler Notch equation: niPVR = 7.1 · (Ejection time/Notch time) − 9.36 (Afonso et al); B) Model 1 vs. iPVR. The paired t-test mean difference is 3.05 with a SD of 3.24 WU and P = 0.0001 and limit of agreement of 3.05 ± 6.35. Model 1: PVR = 10 × Peak TR velocity/RVOT VTI + 0.16; Abbas et al; C) Model 2 vs. iPVR. The paired t-test mean difference is (-) 1.71 with a SD of 3.28 WU and P = 0.018 and limit of agreement of (-) 1.71 ± 6.43. Model 2: PVR = PASP/RVOT VTI + 3, Opotowsky et al; D) Model 3 vs. iPVR. The paired t-test mean difference is (-) 3.70 with a SD of 3.82 WU and P < 0.0001 and limit of agreement of (-) 3.70 ± 7.49. Model 3: PVR = 2.34 + TR PG/RVOT VTI × 1.48, Kouzu et al; E) Model 4 vs. iPVR. The paired t-test mean difference is 0.05 with a SD of 3.56 WU and P = 0.949 and limit of agreement of 0.05 ± 7.00. Model 4: PVR = 5.19 × (TRV2 /RVOT VTI) − 0. 4, Abbas et al; and F) Model 5 vs. iPVR. The paired t-test mean difference is (-) 0.75 with a SD of 3.96 WU and P = 0.360 and limit of agreement of (-) 0.75 ± 7.76. pulmonary vascular resistance index = 1.97 + 190.71 (systolic pulmonary artery pressure/[HR × RVOT VTI]), Haddad et al; for model 5, the estimated pulmonary vascular resistance index was divided by BSA to obtain PVR. Abbreviation as Figures 1 and 3.

Figure 5

Relationship Between PA Systolic Pressure, Pulmonary Vascular Resistance and Disease Progression Schematic outlining relationship between PA systolic pressure, pulmonary vascular resistance and disease progression. PA = pulmonary arterial; RV = right ventricular; other abbreviation as Figure 3.