Effect of cardiac output on mitral valve area in patients with mitral stenosis: Validation and pitfalls of the pressure half-time method

Background and aim of the study: The non-invasive evaluation of mitral valv e area is often used in the assessment of patients with mitral stenosis. Th e pressure half-time method is commonly used to calculate valve area, but i s inaccurate in many clinical scenarios. We sought to quantify the effects of changing cardiac output oil the accuracy of mitral valve area determinat ion. Methods: Thirteen patients with mitral stenosis underwent routine stress ec hocardiography with resting and peak exercise results compared. A previousl y described and clinically validated mathematical model of the cardiovascul ar system was used to validate the clinical results, Seven different loadin g conditions for each of four different stenotic valve areas were modeled. Results: In patients, with increasing cardiac output, pressure half-time de creased (-30.6 +/- 35.3 ms/l/min) and calculated valve area increased by 0. 25 +/- 0.30 cm(2)/l/min. By continuity, it appeared that approximately half of this increase was due to actual valve orifice stretching, the remainder reflecting fundamental changes in the relationship between halftime and va lve area. Mathematical modeling resulted in similar changes in pressure hal f-time and calculated valve area (0.06 to 0.12 cm(2)/l/min, p = 0.20 versus clinical results). Conclusion: Changes in cardiac output result in predictable changes in pres sure half-time, and should be considered when performing serial examination s in patients with mitral stenosis.