TRANSMITRAL PRESSURE HALF-TIME

This is the best way to figure out the mitral valve area in people with bad MR.

A patient with roaring MR will always have a high mean transmitral gradient and therefore you will be alarmed into thinking they have severe MS. But their pressure half-time will be the impartial umpire that sets the record straight***.

The relationship between PHT and DT is that PH Time=29% of the Deceleration Time.

Thus, long deceleration times, as occur in MS or in mild diastolic dysfunction will lead to a longer DT and therefore a longer PHT.

Whereas, anything that raises the LVEDP will lead to a shortened diastolic period of the valve being open (increased LVEDP from significant AI, increased LVEDP from moderate diastolic dysfunction, increased LVEDP from systolic dysfunction, increased LVEDP from listening to Beethoven's 5th) and so will lead to a shortened DT and PHT.

It was figured out, purely by Norwegian luck, that MVA=220/PHT IN ABNORMAL NATIVE VALVES. That's the critical point - that 220 number was only tested in abnormal native valves. Not in prosthetic valves. And not in normal mitral valves. So, the formula CANNOT be used to figure out the mitral valve area in prosthetic valves or in normal mitral valves.

So, for abnormal native mitral valves, MVA=220/PHT

Personally, I prefer to remember, MVA=759/DT (i.e 220/0.29)

Other things to know:
1. In AF, each pressure half-time is different because each diastole is different. So, you need to take an average value from about 10 readings.

2. In the immediate post-valvotomy period, pressure half-time doesn't work to predict MVA because the chamber compliance has still not adjusted. However, by 24 hours, and definitely by 28 hours, it becomes accurate.

http://circ.ahajournals.org/cgi/reprint/circulationaha%3B78/4/980

***so, that's the theory. Does it work in practice?
According to these guys, no:

Does chronic mitral regurgitation influence Doppler pressure half-time–derived calculation of the mitral valve area in patients with mitral stenosis?
American Heart Journal, Volume 148, Issue 4, Pages 703-709
J.Mohan, S.Mukherjee, A.Kumar, R.Arora, A.Patel, N.Pandian

They found that in patients with mild MR, the PHT underestimated the MVA in 17% of patients and overestimated it in 11% of patients (using planimetry MVA as the gold standard)

But when it came to moderate/severe MR, it underestimated it in 35% of patients and overestimated it in 12%.

So, my reading of this study is that if you believe that planimetry is the gold standard, then you will be wrong about ~30% of the time if you use PHT and have mild MR, and wrong ~50% of the time (usually through underestimating the size of the valve area) if you have moderate or severe MR.