Pressure half-time (T½) is a method utilized in echocardiography to determine valvular area in the presence of Mitral Stenosis. T½ measures the decline in pressure across a valve, which is determined by the size of the orifice: the slower the pressure decline, the smaller the orifice area. The pressure halt-time is measured in milliseconds, based on the time it takes for the transmitral blood flow velocity to drop to one half of the maximum diastolic pressure gradient. The flatter the transmitral velocity waveform, the more severe the stenosis.
Formula to determine Mitral Valve Area (MVA) with pressure half-time is MVA = 220/T½ (whereas 220 is a constant derived from catheterization T½ measurement of a valve with the area of 1cm²).
2D echocardiography and cardiac catheterization quantification of pressure half-time result in similar findings. To obtain the MVA with the use of 2D transthoracic echo, the pressure gradient across the MV is gathered in an apical four-chamber position with a Continuous Wave (CW) Doppler beam positioned directly through the MV, which is optimal for gathering the maximum velocity through the orifice. The waveform presented will display antegrade flow (see figure ??): the downward slope can then be measure in two places to determine the speed at which the diastolic pressure drops.
Insert chart of pressure half-time/MVA values.
| Mitral Valve Area | Pressure Half-Time | Severity |
|---|---|---|
| 3 - 5cm² | >Example | Normal |
| Example | Example | Example |
| Example | Example | Example |
| 1cm² | 220 | Severe |
| < 1cm² | Example | Critical |
The T½ formula can also be used to determine the severity of Aortic Insufficieny (AI). A relatively flat slope that registers a pressure half-time of >500ms is considered mild regurgitation, whereas a steep slope that yields a fast pressure drop, <200ms, is considered severe. Moderate AI can range from ____ to _____.
References edit
- ^ Otto, Catherine (2009). Textbook of Clinical Echocardiography, Fourth Edition. Philadelphia, PA: Saunders, an imprint of Elsevier, Inc.
- ^ Smith, M D (1986). "Comparative Accuracy of Two-Dimensional Echocardiography and Doppler Pressure Half-Time Methods in Assessing Severity of Mitral Stenosis in Patients With and Without Prior Commissurotomy". American Heart Association, Inc.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ Gilla, Edward A. "Evaluation of the Severity of Valvular Heart Disease and Timing of Surgery". Revista Español de Cardiológica. University of Washington. Retrieved 6 August 2012.
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