The effect of the duration of the cardiac cycles on determining mitral valve area by means of pressure half-time

To analyze the influence of variations in the length of cardiac cycle length of calculating mitral valve area by means of the pressure half time in patients with mitral valve stenosis and atrial fibrillation. Fifty-nine patients with pure mitral valve stenosis and atrial fibrillation were subjected to transmitral flow measurements by continuous Doppler monitoring from the apical window. In each patient the pressure half time was quantified, corresponding to a minimum of 30 consecutive cycles. Considering all the measurements made in each patient, the correlation between pressure half time and cardiac cycle was significant in 20 cases (34%). The pressure half time variation coefficients were significantly greater when including the values corresponding to the shortest cycles. Thus, for cycle duration of > or = 800, 700, 600, 500 and 400 ms, the mean values were 0.096 +/- 0.041, 0.106 +/- 0.042 (NS), 0.128 +/- 0.032 (p < 0.05), 0.167 +/- 0.048 (p < 0.001) and 0.231 +/- 0.057 (p < 0.0001), respectively. Upon analyzing the relation between pressure half time and cardiac cycle with progressive exclusion of the longer cycles > or = 800, 700 and 600 ms the number of patients with significant correlation coefficients increased to 19/37 (51%), 12/23 (52%) and 4/6 (67%) on respectively excluding. Patients with mitral valve stenosis and atrial fibrillation show a variation in pressure half time that may complicate calculation of the mitral valve area. Variability is inherent to the measurement method, and is furthermore dependent upon cardiac cycle duration. This may be resolved by limiting determinations to cycles longer than 800 ms.