Differences Between the A2P2 and the 2OS

1. When is an OS louder or as loud at the apex as it is at the left sternal border?

ANS: As a rule, this occurs only when the LV is dilated, or if a rib has been removed in previous heart surgery. A P2 is never as loud or louder at the apex than at the left sternal border.

If the second component of a split S2 is louder or as loud at the apex as at the left sternal border, it is probably an OS.

2. How does the effect of respiration affect the loudness of the P2 differently from that of the OS?

ANS: Inspiration makes the P2 louder (more blood is drawn into the right side of the heart with inspiration) and the OS softer (blood is withheld from the left atrium on inspiration so that less blood flows through the mitral valve).

If the second component of an S2 split becomes softer on inspiration at the left lower sternal border (in the absence of LBBB), it is probably a mitral OS.

3. How can you recognize an A2, P2, and OS as a triple second sound?

ANS: A triple S2 can often be recognized along the left sternal border in MS by listening for a snare-drum effect, a "trill," or the "tongue-rolling" Spanish rr effect. The snare-drum triple S2 is most likely to be heard during inspiration, when the P2 pulls away from the A2.

On inspiration, the S2 split opened up into its A2 and P2 components. Together with the OS, a triple second sound is heard that produces a snare-drum effect.

A triple second sound, in which the three sounds are close enough together to sound like a snare drum, implies that an OS is present as the final component.

4. What effect does standing have on the 2-OS interval? Why?

ANS: It widens it. The pooling of blood in the legs decreases venous return to the left atrium. This lowers the pressure behind the obstructed mitral valve. (For why a low pressure in the LA makes a wide 2-OS interval, see Question 3 above under Relation Between the 2-OS Interval and the Severity of Mitral Stenosis.)

5. What effect does standing have on the A2-P2 interval? Why?

ANS: The A2-P2 interval either remains the same or narrows. The reason for this is that although there is a decrease in volume to both ventricles, the right ventricle (RV) responds to the decrease more than does the LV.

If a split second sound becomes wider on standing, its second component is an OS.

6. Why should the presence of an OS imply that the first sound should have a snapping quality?

ANS: If doming of the valve produced the OS, then it should also make a snapping Sj. In other words, a mitral valve that has an OS usually also has a "closing snap."

If the S2 is very soft, the second component of the S2 is not likely to be an OS.

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Blood Pressure Health

Blood Pressure Health

Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...

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