Pulmonary Vascular Resistance in Patients With Pulmonary Hypertension: Importance of the Quadratic Velocity-Pressure Relationship　– Reply –

We thank Dr Abbas for his critical reading of our paper recently published in the Journal.¹ A number of articles have been published by Abbas and others on both the non-invasive determination and the prognostic value of pulmonary vascular resistance (PVR) in patients with pulmonary hypertension (PH).^2–6 All of them noted a reduced accuracy and precision of PVR determined on echocardiography (PVR_ECHO), especially in patients with PVR >6 Wood units (WU). Most studies also determined cut-offs for normal or elevated PVR but, to the best of our knowledge, no equation was deemed to be suitable for an accurate and precise determination of absolute PVR.

Dr Abbas suggested that the use of the updated equation would have been more precise and accurate.² The aim of the study was to compare several equations. We chose the initial equation published in 2003 (TRV/RVOT_TVI×10)⁷ because it is used daily in echocardiographic laboratories in France. We tested other equations (including the one noted) but, given that the results were similar for the PVR calculations, we reported only some of them.

The cut-offs <0.175 and >0.275 for the tricuspid regurgitation velocity/right ventricle outflow tract velocity-time integral (TRV/RVOT_TVI) ratio were used to repartition the original subjects, to distinguish PH with normal from elevated PVR (Figure 1). The majority of patients (65.2%) with TRV/RVOT_TVI <0.175 had PVR >2 WU. For patients with TRV/RVOT_TVI 0.175–0.275 (n=48), the use of the original equation (TRV/RVOT_TVI×10) was globally poor (r=0.38, P=0.01; Figure 2), with a constant underestimation of PVR when the average (PVR_RHC+PVR_ECHO) increased. Only 12 patients had TRV/RVOT_TVI >0.275 (Figure 3). For those particular patients, PVR_RHC was >6 WU in 8 of the 12 patients (66.7%). The equation TRV²/RVOT_TVI×5, however, was not precise enough to calculate PVR, giving an underestimation when the average (PVR_RHC+PVR_ECHO) increased. In the present subjects, TRV/RVOT_TVI <0.175 was not suitable to exclude PVR >2 WU. TRV/RVOT_TVI >0.275 was more sensitive and more accurately predicted elevated PVR >6 WU, but neither of the two equations was sufficiently accurate and precise with the echocardiography data.

Figure 1.

Repartition of the subjects according to tricuspid regurgitation velocity/right ventricle outflow tract velocity-time integral (TRV/RVOT_TVI). PVR, pulmonary vascular resistance.

Figure 2.

(Left) Correlation between pulmonary vascular resistance (PVR) determined on right heart catheterization (PVR_RHC) or echocardiography (PVR_ECHO), and (Right) Bland-Altman analysis of PVR_ECHO and PVR_RHC in patients with tricuspid regurgitation velocity/right ventricle outflow tract velocity-time integral (TRV/RVOT_TVI) 0.175–0.275. Red dotted lines, 95% limit of agreement. Continuous line, positive relationship between the two parameters.

Figure 3.

(Left) Correlation between pulmonary vascular resistance (PVR) determined on right heart catheterization (PVR_RHC) or echocardiography (PVR_ECHO), and (Right) Bland-Altman analysis of PVR_ECHO and PVR_RHC in patients with tricuspid regurgitation velocity/right ventricle outflow tract velocity-time integral (TRV/RVOT_TVI) >0.275. Red dotted lines, 95% limit of agreement. Continuous line, positive relationship between the two parameters.

But is the determination of absolute PVR so important? We believe that it is, and in the last European guidelines, PVR (cut-off=3 WU) was included in the hemodynamic definition of pulmonary arterial hypertension.⁸ If, however, the variations in PVR_ECHO are similar (ie, in the same direction and with the same amplitude) to the changes in PVR_RHC (regardless of the absolute value), echocardiography could play a more important role in the follow-up of PH. Further longitudinal studies with multiple assessments of both PVR_ECHO and PVR_RHC are required.

• Stéphane Doutreleau, MD, PhD
• Matthieu Canuet, MD
• Irina Enache, MD, PhD
• Paola Di Marco, MD, PhD
• Anne Charloux, MD, PhD
• Department of Physiology, INSERM U1042, Grenoble (S.D.);
• Department of Pneumology (M.C.),
• Department of Physiology (I.E., P.D.M., A.C.), New Hospital, Strasbourg, France

(Released online November 9, 2016)

References

• 1.    Doutreleau  S,  Canuet  M,  Enache  I,  Di Marco  P,  Lonsdorfer  E,  Oswald-Mammoser  M, et al. Right heart hemodynamics in pulmonary hypertension: An echocardiography and catheterization study. Circ J 2016; 80: 2019–2025.
• 2.    Abbas  AE,  Franey  LM,  Marwick  T,  Maeder  MT,  Kaye  DM,  Vlahos  AP, et al. Noninvasive assessment of pulmonary vascular resistance by Doppler echocardiography. J Am Soc Echocardiogr 2013; 26: 1170–1177.
• 3.    Opotowsky  AR,  Clair  M,  Afilalo  J,  Landzberg  MJ,  Waxman  AB,  Moko  L, et al. A simple echocardiographic method to estimate pulmonary vascular resistance. Am J Cardiol 2013; 112: 873–882.
• 4.    Kouzu  H,  Nakatani  S,  Kyotani  S,  Kanzaki  H,  Nakanishi  N,  Kitakaze  M. Noninvasive estimation of pulmonary vascular resistance by Doppler echocardiography in patients with pulmonary arterial hypertension. Am J Cardiol 2009; 103: 872–876.
• 5.    Vlahos  AP,  Feinstein  JA,  Schiller  NB,  Silverman  NH. Extension of Doppler-derived echocardiographic measures of pulmonary vascular resistance to patients with moderate or severe pulmonary vascular disease. J Am Soc Echocardiogr 2008; 21: 711–714.
• 6.    Ajami  GH,  Cheriki  S,  Amoozgar  H,  Borzouee  M,  Soltani  M. Accuracy of Doppler-derived estimation of pulmonary vascular resistance in congenital heart disease: An index of operability. Pediatr Cardiol 2011; 32: 1168–1174.
• 7.    Abbas  AE,  Fortuin  FD,  Schiller  NB,  Appleton  CP,  Moreno  CA,  Lester  SJ. A simple method for noninvasive estimation of pulmonary vascular resistance. J Am Coll Cardiol 2003; 41: 1021–1027.
• 8.    Galie  N,  Humbert  M,  Vachiery  JL,  Gibbs  S,  Lang  I,  Torbicki  A, et al. 2015 ESC/ERS Guidelines for the diagnosis and treatment of pulmonary hypertension: The Joint Task Force for the Diagnosis and Treatment of Pulmonary Hypertension of the European Society of Cardiology (ESC) and the European Respiratory Society (ERS): Endorsed by Association for European Paediatric and Congenital Cardiology (AEPC), International Society for Heart and Lung Transplantation (ISHLT). Eur Respir J 2015; 46: 903–975.