title: Value and limitations of peak-to-peak gradient for evaluation of aortic stenosis.
abstract: OBJECTIVE
  In patients with aortic stenosis (AS), it has been reported that the transvalvular pressure gradients (APs) may be reduced or even abolished in the presence of concomitant arterial hypertension, but the mechanisms underlying this phenomenon remain unclear. The study aim was to: (i) examine the relationship between systemic arterial hemodynamics and the peak-to-peak (deltaP(PtoP)), peak deltaP and mean deltaP; and (ii) propose and validate a new formula for the non-invasive estimation of the deltaP(PtoP) and of the peak left ventricular systolic pressure (LVSP) using Doppler echocardiography.
  
  
  METHODS
  Two fixed stenoses (geometric orifice area 1.0 and 1.35 cm2) and one bioprosthesis (effective orifice area (EOA) 1.2 cm2) were tested in a mock flow circulation model. Systemic vascular resistance (R) was increased from 1,500 to 3,300 dyne.s/cm5, and systemic arterial compliance (C) was decreased from 2.9 to 0.9 ml/mmHg, while transvalvular flow was held constant.
  
  
  RESULTS
  Neither C nor R had any significant impact on EOA, peak deltaP and mean deltaP. deltaP(PtoP) was decreased markedly, however, when C was reduced (bioprosthesis: -15 mmHg (-69%); orifice 1.35 cm2: -24 mmHg (-30%); cm2: (-13%)). Subsequently, an equation was proposed to predict deltaP(PtoP) from EOA, mean deltaP, and C measured by Doppler echocardiography. LVSP calculated by adding the predicted deltaP(Ptop) to systolic arterial pressure (SAP) was compared with LVSP measured directly in a dataset of 24 pigs with experimentally induced AS. There was a strong agreement between the estimated and measured LVSP (r = 0.97; mean absolute error 5 +/- 5 mmHg).
  
  
  CONCLUSIONS
  deltaP(Ptop) should not be used to evaluate AS severity because, as opposed to peak and mean deltaPs, it is highly influenced by C. The new non-invasive method proposed in this study to estimate the LVSP may be useful for obtaining a more accurate estimate of global LV afterload in patients with AS.
authors.affiliation: Biomedical Engineering Laboratory, Clinical Research Institute of Montreal, Montreal, Quebec, Canada. lyes.kadem@ircm.qc.ca
authors.forename: Lyes
authors.initials: L
authors.lastname: Kadem
authors.forename: Damien
authors.initials: D
authors.lastname: Garcia
authors.forename: Louis-Gilles
authors.initials: LG
authors.lastname: Durand
authors.forename: Régis
authors.initials: R
authors.lastname: Rieu
authors.forename: Jean-Gaston
authors.initials: JG
authors.lastname: Dumesnil
authors.forename: Philippe
authors.initials: P
authors.lastname: Pibarot
mesh_terms: D000818:Animals; D001024:Aortic Valve Stenosis / Q000000981:diagnostic imaging / Q000503:physiopathology* / Q000601:surgery; D001705:Bioprosthesis; D001783:Blood Flow Velocity; D004195:Disease Models, Animal; D015150:Echocardiography, Doppler; D006350:Heart Valve Prosthesis; D012107:Research Design; D013552:Swine; D014655:Vascular Resistance; D016277:Ventricular Function, Left; D017725:Ventricular Pressure