The pressure halftime across the mitral valve is defined as the time interval between the maximum gradient across the mitral valve in early diastolic up until the point where the gradient becomes half the initial value. It is expressed in milliseconds.
The mitral valve area is inversely related to the pressure halftime. In individuals atrial fibrillation, the diastolic slope tends to be a lot longer and hence the average of five cycles should be taken. However, sometimes the pressure halftime may not be very useful in assessing mitral stenosis in such patients.
The pressure half-time depends primarily on the mitral valve area and less so upon the heart rate. In individuals who have significant aortic regurgitation, there is an increase in the left ventricular end-diastolic pressure. This alters the diastolic gradient between the left ventricle and the left atrium, decreasing the pressure halftime and thus resulting in an overestimation of the mitral valve area.
Similarly, in individuals who have left ventricular hypertrophy, the left ventricular relaxation may be abnormal. In such patients the pressure half-time is prolonged and the mitral valve area is hence underestimated.
In patients who have atrial septal defects, the left-right shunt alters the gradient between the left atrium and the left ventricle. This reduces pressure halftime and hence overestimates mitral area.
In simple terms,
Severe AR - Overestimation
ASD - Overestimation
Abnormal LV relaxation - Underestimation.
The mitral valve area is inversely related to the pressure halftime. In individuals atrial fibrillation, the diastolic slope tends to be a lot longer and hence the average of five cycles should be taken. However, sometimes the pressure halftime may not be very useful in assessing mitral stenosis in such patients.
Mitral Valve Area = 220 / Pressure Half Time (ms)
The pressure half-time depends primarily on the mitral valve area and less so upon the heart rate. In individuals who have significant aortic regurgitation, there is an increase in the left ventricular end-diastolic pressure. This alters the diastolic gradient between the left ventricle and the left atrium, decreasing the pressure halftime and thus resulting in an overestimation of the mitral valve area.
Similarly, in individuals who have left ventricular hypertrophy, the left ventricular relaxation may be abnormal. In such patients the pressure half-time is prolonged and the mitral valve area is hence underestimated.
In patients who have atrial septal defects, the left-right shunt alters the gradient between the left atrium and the left ventricle. This reduces pressure halftime and hence overestimates mitral area.
In simple terms,
Severe AR - Overestimation
ASD - Overestimation
Abnormal LV relaxation - Underestimation.
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