Recent reports have emphasized the limitations of aortic valve area estimations using the Gorlin formula based on the Toricelli model. Since aortic valve resistance (AVR) does not use a constant and treats the pressure gradient and the cardiac output without favouring either, it has been proposed as a more accurate index of the severity of aortic stenosis. Though it has previously been calculated using pressure and flow parameters obtained in the catheterization laboratory, it is possible to derive the valve resistance using Doppler echocardiography. Doppler-echo estimates of AVR may be used as an alternative index of aortic stenosis severity; however, no data exists as to its accuracy compared with cardiac catheterization derived AVR. Thirty-nine patients with aortic stenosis undergoing invasive hemodynamic and Doppler-echo evaluations were studied. The AVR was calculated using the formula: (mean pressure gradient)/(flow per systolic ejection period). The cardiac output at catheterization was measured by using thermodilution technique, whilst the Doppler-echo method utilized the product of velocity time integral of the flow in left ventricular outflow tract and its cross sectional area. The Doppler-echo derived AVR (38.5 to 738.2 dyne.sec.cm-5) correlated significantly (r = 0.82, p < 0.0001, S.E.E. = 75.0 dyne.sec.cm-5) with independently derived catheterization values (53.6 to 738.8 dyne.sec.cm-5). There was a good correlation between mean gradient obtained by both modalities.
Conclusion: Doppler-echo AVR correlates well with catheterization AVR and may provide an additional non-invasive parameter of aortic stenosis severity.