Sites of A2 and P2 Loudness

1. What is wrong with using the expression "A2 is louder than P2," or vice versa?

ANS: If by A2 is meant the entire second sound in the second right interspace and by P2 is meant the entire second sound in the second left interspace (as was true before 1960), then it has no meaning. If it refers to individual components of a split second sound, then "A2 is louder than P2," or vice versa may have meaning.

2. Which component of the S2 is best heard in normal subjects at the second left interspace (formerly called the "pulmonary area")? What is the clinical significance of this?

ANS: Not only is the A2 louder than the P2 in the second left interspace in 70% of normal subjects in all age groups, but also in subjects over age 20 the A2 is always normally louder than the P2 in the second left interspace [2]. This, together with the fact that the P2 is often best heard in the third or fourth left interspace, rules out the second left interspace as truly a pulmonary area. Because this term is misleading, we encourage use of the term second left interspace instead.

3. Where is the A2 normally heard on the chest wall?

ANS: Anywhere that one would normally listen for heart sounds.

4. Where is the P2 normally heard on the chest wall?

ANS: In adults the P2 is normally heard all along the left sternal border, often only a few centimeters to the left of the sternum. In infants and young children and in young adults with a thin chest wall and a narrow anteroposterior chest diameter, it may also be heard at the apex.

Note: This implies that if the P2 (split S2) is also heard to the right of the sternum or at the apex in a thick-chested adult, the P2 is probably louder than normal. When the P2 is heard unexpectedly at the apex, you will usually find that the RV is enlarged and the apex beat is not due to the LV but entirely to the RV. Thus, in atrial septal defects (ASDs) it is expected that the large RV will make the P2 audible at the apex, even though there may be no pulmonary hypertension.

5. Where is the splitting of the S2 most often appreciated on the chest wall?

ANS: At the second or third left interspace parasternally.

Note: In cyanotic tetralogy of Fallot, the S2 is usually single and consists entirely of the A2 because the P2 is attenuated by a. A deformed pulmonary valve when there is valvular stenosis.

This simultaneous carotid pulse tracing and phonocardio-gram is from a normal 16-year-old with a normal split of S2 on inspiration. Note that (1) only the A2 would be audible at the apex, and (2) the A2 has a greater amplitude than the P2 at the second left interspace (Second LIS).

b. The anterior placement of the aorta relative to a posteriorly placed pulmonary artery.

c. S2 splitting is best heard to the right of the sternum in dextrocardia and transposition of the great vessels.

6. Where is the aortic component of the S2 usually heard best in normal subjects of all ages?

ANS: At the second and third left interspaces, probably because the aortic valve is situated behind the sternum, close to this area. This fact further denies that the second right interspace should be called the aortic area, as it is in most of the auscultation literature.

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