The Narrowly Split S2

1. List the usual causes of a narrowly split S2 due to a delayed A2.

ANS: a. Conditions that cause electrical delay of LV conduction, such as left bundle branch block (LBBB).

b. Conditions that increase the volume of the LV but without an extra outlet (a VSD or mitral regurgitation [MR] is an extra outlet), e.g., persistent ductus arteriosus (PDA) and AR.

c. Conditions that cause a significant gradient across the outflow tract of the LV (e.g., AS), so that there is a delay in LV pressure dropping below aortic pressure.

<?,' \<i> In AS the LV pressure rises high above aortic pressure during systole. It then takes so long to ! \ drop down to aortic diastolic pressure and close the valve that the incisura is low and late on i *

the aortic pressure curve. The A2 is also late because it is simultaneous with the incisura.

in AS

2. The S2 is single on quiet inspiration in about what percentage of normal subjects (a) under age 50 and (b) over age 50?

ANS: The S2 is single.

a. In about 30% of subjects under age 50.

Note: Prolongation of LV isovolumic contraction time contributes to the delayed A2 and narrowness of the split S2 with aging.

3. How can you tell that an S2 is split on inspiration even if you do not hear two distinct components?

ANS: If the S2 is clean and sharp on expiration and becomes impure or rough on inspiration.

4. What kinds of respiration will obscure awareness of whether the split moves besides rapid respiration?

ANS: a. Too deep an inspiration will interpose too much lung between the stethoscope and the heart, causing one or both of the S2 components to disappear.

b. Too shallow an inspiration may not open the S2 at all. Note: If you raise your arm for inspiration and lower it for expiration, you may "conduct" respiration so that there are at least two or three cycles during each phase of respiration. Be certain that the patient does not breathe too deeply.

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