Effect of heart rate on transmitral flow velocity profile and Doppler measurements of mitral valve area in patients with mitral stenosis

To study the effect of heart rate changes on Doppler measurements of mitral valve area atrial pacing was performed in 14 patients with mitral stenosis andsinus rhythm. Continuous wave Doppler and haemodynamic measurements were performed simultaneously at rest and during pacing-induced tachycardia. (1) Mitral valve area was determined using the conventional pressure half time method. (2) Additionally, mitral valve area was calculated with a combined Doppler and thermodilution technique according to the continuity equation. (3) Simultaneous invasive measurements were used for calculation of the mitral valve area according to the Gorlin formula. With increasing heart rate (69 ± 13−97 ± 15−114 ± 13 beats min−1) mitral valve area either determined by the continuity equation (1.0 ± 0.2−1.0 ± 0.3−1.1± 0.4 cm2) or the Gorlin formula (1.2±0.3−1.2±0.4−1.3±0.4cm2) remained constant. Both methods correlated closely not only at rest (r=0.88, SEE=0.11 cm2, P<0.001), but also during atrial pacing (first level: r=0.95, SEE=0.10 cm2, P<0.001 second level: r=0.95, SEE=0.13 cm2, P<0.001). In contrast, mitral valve area calculated according to the pressure half time method increased significantly during atrial pacing (1.0 ± 0.3−1.8 ±0.5 − 2.O ± 0.5 cm2). Mitral valve area determined either by the pressure half time method or the Gorlin formula correlated in patients with heart rates ≤80 beats min−1 (r=0.75, SEE = 0.15 cm2, p <0.01), while no significant correlation was found in patients with heart rates above 80 beats min−1. Our conclusion is that while the pressure half time method progressively overestimates mitral valve area with increasing heart rate, the accuracy of the continuity equation method based on a combined Doppler/thermodilution technique is independent of heart rate changes in patients with mitral stenosis and sinus rhythm. This method is superior to the pressure half time method in patients with mitral stenosis and heart rates exceeding 80 beats min−1.