AMA Category 1 Credit for Physicians Only.
ASRT CME is not available.
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The measurement method is called the Pressure Half-Time method. The concept of pressure half-time is based upon diastolic rate of flow across the mitral valve measured by continuous wave Doppler. As the mitral valve area decreases, the flow across the mitral valve becomes closer or exceeds a pan-diastolic time period. When the flow becomes pan-diastolic, the pressure gradient must rise to fill the left ventricle and the Vmax of the diastolic flow increases. The slope of the Vmax to the end of the rapid filling phase correlates with the mitral valve area. This was standardize to the time it takes the pressure to decrease by half, hence the pressure half time or PHT. Normal pressure half-time is 20-60 msec. PHT is insensitve to MR, atrial fibrillation, or exercise and replaced the Gorlin formula. A PHT > 220 msec correlated with a MVA < 1.0 cm2.
Mitral valve gradients are sensitive to cardiac output, rising as the flow rises. 2D planimetry, while a useful tool, depends upon a perpendicular cut across the mitral valve which may be difficult to obtain.
PHT decreases with aortic regurgitation that is moderate or severe. Since AR is filling up the ventricle at the same time as the atrium, the left ventricular pressure rises faster and the PHT will be falsely shorter than if the AR was absent. One study reported that only severe AR affects the PHT while moderate AR does not.
Similarly, patients with increased left ventricular stiffness (diastolic dysfunction), the pressure in the left ventricle will rise faster, thereby decreasing the PHT and overestimating the MVA by PHT.
MVG and PHT doe not correlate well with the MVA calculation by continuity equation after a mitral valve repair. Continuity equation should be used for MVA calculation after a MV repair in one study.
Finally, atrial fibrillation as reported above does not affect PHT. However, one study from JASE showed that patients in NSR tended to have normal atrial-ventricular compliance and overestimated the MVA by PHT whereas patients with atrial fibrillation had increased compliance and underestimated the MVA by PHT when compared to 2D measurements. The article pointed out that it was the compliance that affected the PHT, however, most patients with atrial fibrillation had abnormal compliance.
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Impact of cardiac rhythm on mitral valve area calculated by the pressure half time method in patients with moderate or severe mitral stenosis.
Atrioventricular Pressure Half-Time
A comparison of the assessment of mitral valve area by continuous wave Doppler and by cross sectional echocardiography.
Mitral valve area by the pressure half-time method does not correlate with mean gradient in mitral valve repair patientsâ‚Ç¨
Aortic regurgitation shortens Doppler pressure half-time in mitral stenosis: clinical evidence
in vitro simulation and theoretic analysis
Limitations of the Pressure Half-Time Method for Estimating Mitral Valve Area in the Presence of Atrial Flutter
Mitral pressure half-time technique for assessing severity of mitral stenosis: essential parameters
Effect of aortic regurgitation on the assessment of mitral valve orifice area by Doppler pressure half-time in mitral stenosis.
Reassessment of valve area determinations in mitral stenosis by the pressure half-time method: impact of left ventricular stiffness and peak diastolic pressure difference.
Doppler pressure half-time method of assessing mitral valve area: Aortic insufficiency does not adversely affect validity