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

To the Editor:

Doutreleau et al published an article on echocardiography/catheterization comparing simultaneous hemodynamic parameters according to right heart catheterization and Doppler.¹ They concluded that echocardiography was a good method with which to assess the presence of pulmonary hypertension, but that echocardiography cannot be used to accurately determine pulmonary capillary wedge pressure or pulmonary vascular resistance (PVR). Their study provided almost simultaneous assessments of hemodynamics, and the authors should be complimented on their effort.

The authors, however, referenced a paper published in 2003 that investigated patients with the majority of PVR around 2 Wood units.² The main goal was to establish the relationship between tricuspid regurgitation velocity/right ventricle outflow tract velocity-time integral (TRV/RVOT_TVI) and PVR and set a cut-off for elevated PVR. Since then, multiple studies in >2,000 patients have confirmed the prognostic value of the ratio TRV/RVOT_TVI itself, and also the cut-off TRV/RVOT_TVI >0.175 as a marker of elevated PVR. Moreover, multiple studies have also suggested that the equation PVR=TRV/RVOT_TVI×10 lacks accuracy at higher PVR, but appears to work well with lower PVR.

We thus published a paper in 2013 that assessed a wider range of patients with higher PVR, and derived an algorithm for use with a wider range of PVR.³

Simply stated, if TRV/RVOT_TVI >0.275, then TRV has to be squared and the equation PVR=(TRV²/RVOT_TVI×5.19)–0.4, simplified to TRV²/RVOT_TVI×5.

Given that the transpulmonary pressure is related to the square of the velocity and not to the absolute linear velocity, the higher the pressure, the higher the absolute difference between the absolute linear velocity and the quadratic velocity, and the TRV² equation should be used.

It would be prudent that the authors utilize the updated equation in their paper, given that they have included a higher number of patients with pulmonary hypertension. Moreover, assessing how often the TRV/RVOT_TVI cut-off of 0.175 was able to accurately assess elevated PVR, would also be helpful in their study.

• Amr El Sayed Abbas
• Cardiovascular Medicine, Beaumont Health System, Royal Oak, MI, USA

(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,  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.
• 3.    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.