Simplified formula for the calculation of mitral valve area: potential inaccuracies in patients with tachycardia.

A simplified formula (cardiac output/[transvalvular pressure gradient]1/2) has been proposed as an alternative to the Gorlin equation for determining valve area in patients with mitral stenosis. This study was done (a) to assess the relationship between the results of the simplified formula and those of the Gorlin equation in patients with mitral stenosis and (b) to determine the clinical characteristics most likely to be associated with a disparity between the 2 formulae. In 96 patients with mitral stenosis, the disparity between the 2 formulae was greater than 0.2 cm2 in 43 (45%) and greater than or equal to 0.35 cm2 in 21 (22%). The results of the simplified formula were especially likely to be disparate from those of the Gorlin equation in those whose heart rates were greater than 100 beats/minute. Thus, in the patient with mitral stenosis, the simplified formula should be used with caution and cognizance of its potential inaccuracy, particularly if the patient is tachycardic.