And The Severity Of Mitral Stenosis

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1. What are the major factors controlling the duration of isovolumic relaxation, or the 2-OS interval?

ANS: a. The pressure at which the aortic valve closes (near systolic pressure). b. The pressure in the LA at the time the mitral valve opens.

2. What is the relationship between the degree of MS and the height of the V wave in the LA?

ANS: The greater the stenosis, the greater the obstruction to flow and thus the slower and more incomplete is the emptying of the LA. Therefore, the greater the MS, the higher is the V wave.

Note: This will be clear only if you recall that the V wave is built up during ventricular systole when the mitral valve is closed. If the LA did not empty well in diastole due to MS, the V wave will start to build up from an already high pressure.

Mitral Stenosis Wave

Systole Diastole

The opening snap is produced by the belly of the stenotic anterior leaflet bulging or doming downward with a jerk to produce a clicking or snapping sound. The anterior leaflet, therefore, must also close with a snap as it domes upward. The posterior leaflet has too short a ring-to-free edge distance to produce a "belly snap."

Systole Diastole

The opening snap is produced by the belly of the stenotic anterior leaflet bulging or doming downward with a jerk to produce a clicking or snapping sound. The anterior leaflet, therefore, must also close with a snap as it domes upward. The posterior leaflet has too short a ring-to-free edge distance to produce a "belly snap."

3. Does a high left atrial pressure make the 2-OS interval shorter or longer? Why? ANS: Shorter, because the LV pressure does not have to fall so far to open the

3. Does a high left atrial pressure make the 2-OS interval shorter or longer? Why? ANS: Shorter, because the LV pressure does not have to fall so far to open the

Pulmonary Stenosis Severity

A2 OS OS

Note that the distance between the A2 and the OS is shorter with the higher left atrial pressure.

A2 OS OS

Note that the distance between the A2 and the OS is shorter with the higher left atrial pressure.

4. List the causes of a late OS aside from a mild degree of MS or a heavily calcified mitral valve.

ANS: a. Poor myocardial function due to either damage or aging. This causes prolongation of the isovolumic relaxation time. (Isovolumic relaxation time also increases strikingly with age.)

b. Aortic regurgitation (AR). This is presumably due to the AR jet striking the underbelly of the anterior mitral leaflet and preventing rapid downward excursion of the valve belly. (AR may even eliminate an OS.)

c. High aortic pressure. If the aortic valve closes at a high pressure, more time will be required for the LV pressure to drop below LA pressure to open the mitral valve and create the OS.

5. Which is more reliable in predicting the degree of MS, a narrow 2-OS interval or a wide one? Why?

ANS: A narrow 2-OS is more reliable because there is not much besides tight MS or a tachycardia that can narrow a 2-OS interval, whereas there are at least five causes besides mild MS for a wide 2-OS.

Aortic curve at high pressure

Aortic curve at low pressure

LV pressure curve

L. atrial pressure in mitral stenosis

Note that the higher the aortic pressure the longer the A2-OS interval.

6. Without a phonocardiograph, how can you estimate the width of the 2-OS interval?

ANS: a. If you say "pa-pa" as quickly as possible, you will be separating the sounds by about 100 ms (0.01 s). This is close to the widest possible 2-OS interval.

b. If you say "pa-da" as quickly as possible, you should be able to separate the sounds by about 50-70 ms (0.05-.07 s). This is a narrow 2-OS and suggests moderate to tight MS.

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