The simplified formula for the calculation of aortic valve area: potential inaccuracies in patients with bradycardia or tachycardia.

Abstract

Since the Gorlin equation for calculation of aortic valve area is somewhat complicated, a simplified formula has been introduced in which the cardiac output (in liters/min) is divided by the square root of the peak pressure gradient across the valve (in mmHg), yielding a valve area in cm2. This study was done to examine the reliability of this simplified formula in patients with bradycardia or tachycardia. In 68 patients with aortic stenosis, aortic valve area was calculated with both formulae, and the results were compared with one another. In the 43 individuals whose heart rates were 65 to 100 beats/min, the results of the Gorlin equation and the simplified formula showed excellent agreement (absolute percentage difference, 8 +/- 8% [mean +/- SD]). In contrast, in the 25 patients whose heart rates were less than 65 or greater than 100 beats/min, the absolute percentage difference between the results of the two formulae was 18 +/- 13% (p less than 0.001). Although the results of the two equations were especially likely to be disparate in these patients, there was no predictable relationship between them. Thus, in patients with bradycardia or tachycardia, the simplified formula should be utilized with caution and cognizance of its potential inaccuracy.