12 May

The Natural History and Rate of Progression of Aortic Stenosis: Thoughts for the Future

The Natural History and Rate of Progression of Aortic Stenosis: Thoughts for the FutureTorricelli’s law, the first hydraulic formula that the Gorlin’s used to develop their formula for the calculation of valve area, states that flow is directly proportional to orifice area and flow velocity. Measurements of aortic valve area are made at a single point in time, and thus are based on the assumption that orifice area remains constant throughout ejection. During each ejection, transvalvular flow and pressure gradient increase from zero, reach a peak, and then decrease back to zero. Effective orifice area should thus be constantly changing throughout ventricular systole. Doppler echocardiography will allow one to measure instantaneous aortic valve area at different times during ejection. buy zyrtec online

When 26 patients with valvular aortic stenosis were evaluated, significant changes in effective aortic orifice area were identified during ejection. The peak and mean transvalvular gradients were 82 ±24 mm Hg and 50 ±19 mm Hg, respectively, and the valve area calculated was 0.7±0.3 cm2. When valve area was calculated at the mid-acceleration point of the flow velocity, it was 84 ±15% of the valve area at peak velocity (p<0.0001) and 113±17% (p<0.01) of the valve area at peak velocity when calculated at mid-deceleration. In normal subjects, the valve area remained constant during ejection. This indicates that the stenotic valve opens slowly and continues to open during ejection where the normal valve opens rapidly to its full effective orifice size. As well, the magnitude of change in effective orifice area did not correlate with the usual indexes of hemodynamic severity such as valve area at peak velocity and pressure gradient.
When Doppler echocardiography was used to assess the physiologic response to exercise in 28 asymptomatic patients with aortic stenosis, a subgroup of patients showed an increase in aortic flow velocity during exercise that was less than expected should their orifice area be fixed.

Categories: Aortic Stenosis
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