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[Pressure gradient across the mitral valve in mitral stenosis estimated by high pulse repetition frequency Doppler
Abstract:
High pulse repetition frequency (HPRF) Doppler and continuous wave (CW) Doppler methods were used to estimate the pressure gradient across the mitral valve. Twenty-two cases of mitral stenosis and five cases of ischemic heart disease were studied. Both the HPRF and CW Doppler studies were conducted during catheterization in all cases. In the Doppler study, pressure gradient was calculated using the simplified Bernoulli's formula. The HPRF device used was a type SSD-730 produced by Aloka Co. It had a reference frequency of 2 MHz. Its minimum pulse repetition frequency was 4.2 KHz; its maximum, 19.2 KHz. Among the 27 cases, the maximum flow velocity measured by the HPRF method at the level of the mitral valve orifice was compared with that by the CW method. As the velocity increased, the discrepancy of measured values between the two methods increased, but it was within 0.1 m/sec. Therefore, there was a good correlation between the HPRF and CW methods (r = 0.98). The pressure gradient between time delay-corrected pulmonary artery wedge pressure and left ventricular pressure was compared with that obtained by the HPRF method. Contrary to our expectations, the correlation coefficient between the two was not so high, and the pressure gradients calculated by the HPRF method tended to be underestimated. For eight patients in whom the left atrial pressure could be recorded, the pressure gradient between the left atrium and left ventricle was compared with that obtained by the HPRF method. There was underestimation, and a good correlation coefficient was obtained. When using pulmonary artery wedge pressure as a substitute for left atrial pressure, one must realize that the time delay varies in every case and that the pressure pulse itself is not the same. When the pressure gradient between the left atrium and left ventricle is used, a good correlation coefficient can be obtained. Therefore, the flow velocity obtained by the HPRF method will reflect the true pressure gradient across the mitral valve. The HPRF method proved to have a potential equal to that of the CW method for estimating mitral valve flow velocity in mitral stenosis, and it may be used as a helpful diagnostic tool.