COMPARISON OF VALVULAR RESISTANCE, STROKE WORK LOSS, AND GORLIN VALVEAREA FOR QUANTIFICATION OF AORTIC-STENOSIS - AN IN-VITRO STUDY IN A PULSATILE AORTIC FLOW MODEL

Background Valvular resistance and stroke work loss have been proposed as alternative measures of stenotic valvular lesions that may be less flow dependent and, thus, superior over valve area calculations for t he quantification of aortic stenosis. The present in vitro study was d esigned to compare the impacts of valvular resistance, stroke work los s, and Gorlin valve area as hemodynamic indexes of aortic stenosis. Me thods and Results In a pulsatile aortic flow model, rigid stenotic ori fices in varying sizes (0.5, 1.0, 1.5, and 2.0 cm(2)) and geometry wer e studied under different hemodynamic conditions. Ventricular and aort ic pressures were measured to determine the mean systolic ventricular pressure (LVSP(m)) and the transstenotic pressure gradient (Delta P-m) . Transvalvular flow (F-m) was assessed with an electromagnetic flowme ter. Valvular resistance [VR=1333 . (Delta P-m/F-m)] and stroke work l oss [SWL=100 . (Delta P-m/LVSP(m))] were calculated and compared with aortic valve area [AVA=F-m/(50 root Delta P-m)]. The measurements were performed for a large range of transvalvular flows. At low-flow state s, flow augmentation (100-->200 mL/s) increased calculated valvular re sistance between 21% (2.0-cm(2) orifice) and 66% (0.5-cm(2) orifice). Stroke work loss demonstrated an increase from 43% (2.0 cm(2)) to 100% (1.0 cm(2)). In contrast, Gorlin valve area revealed only a moderate change from 29% (2.0 cm(2)) to 5% (0.5 cm(2)). At physiological flow r ates, increase in transvalvular flow (200-->300 mL/s) did not alter ca lculated Gorlin valve area, whereas valvular resistance and stroke wor k loss demonstrated a continuing increase. Our experimental results we re adopted to interpret the results of three clinical studies in aorti c stenosis. The flow-dependent increase of Gorlin valve area, which wa s found in the cited clinical studies, can be elucidated as true furth er opening of the stenotic valve but not as a calculation error due to the Gorlin formula. Conclusions Within the physiological range of flo w, calculated aortic valve area was less dependent on hemodynamic cond itions than were valvular resistance and stroke work loss, which varie d as a function of flow. Thus, for the assessment of the severity of a ortic stenosis, the Gorlin valve area is superior over valvular resist ance and stroke work loss, which must be indexed for flow to adequatel y quantify the hemodynamic severity of the obstruction.