Hakki's formula for measurement of aortic valve area by magnetic resonance imaging

Hakki's formula (simplified Gorlin formula) can be used during cardiac catheterization to calculate the stenosed cardiac valve areas and can also be adapted to magnetic resonance imaging (MRI) to measure the stenosed cardiac valve areas. We evaluated the reliability of this approach to determine the severity of aortic stenosis compared to the continuity equation using transthoracic echocardiography and planimetry using MRI. We included all eligible symptomatic patients with known aortic stenosis referred to our department during a 1-year period. The aortic valve area (AVA) was estimated using Hakki's formula (MRI), planimetry (MRI), and the continuity equation (transthoracic echocardiography). The agreement among the measurement methods was analyzed using the Bland-Altman method. A total of 63 patients were included (mean age 72 +/- 10 years, 35 men [56%]). The mean AVA was 0.70 +/- 0.21 cm(2) using the continuity equation (transthoracic echocardiography), 0.67 +/- 0.18 cm(2) using planimetry (MRI), and 0.64 +/- 0.21 cm(2) using Hakki's formula (MRI). The mean difference was 0.03 cm(2) (95% limits of agreement -0.32 to 0.25) between planimetry and the continuity equation, 0.05 cm(2) (95% limits of agreement -0.40 to 0.29) between Hakki's formula and the continuity equation, 0.02 cm(2) (95% limits of agreement -0.20 to 0.25) between Hakki's formula and planimetry. The inter- and intraobserver reproducibility using Hakki's formula was excellent. In conclusion, measurement of the AVA using Hakki's formula yielded similar results to those obtained using planimetry and slightly different ones from those obtained using the continuity equation. However, Hakki's formula has the advantage of being easy to use, fast, and reproducible and can be used regardless of the status of the valve (in contrast to planimetry).