Wednesday, February 1, 2017

Second Heart sounds: Quick review

Hello everyone,
Heart sounds are quite interesting and musical topic, something that makes more sense by practicing rather than just reading theoretically. This post is completely dedicated to second heart sound.

Second heart sound (S2)
It is produced during closure of pulmonary and aortic valve.
It is a high pitched sound.
As there is pressure difference in left and right ventricle, the valves don't close at the same time.
Hence, we have two components of S2: Aortic (A2) and Pulmonic (P2) component.

A2 occurs before P2
Why?
1) Left ventricle being more muscular, it completes its systole earlier than right ventricle. 
2) Difference in pressure of aorta and pressure in pulmonary artery.

Physiological respiratory variation:

During inspiration, there is an increase in preload to the right atrium, while decreased preload on left side. Hence, P2 is delayed, since it takes more time to pump out the excess blood (right side) and A2 is earlier since it empties quickly (left side). Conclusion, the split is wider during inspiration.

During expiration, the exact opposite happens. P2 empties relatively earlier than the time it took during inspiration and A2 takes a little longer than the time it took to pump out blood during inspiration. The split narrows and is not heard.

Normally, split is variable. Present during inspiration, while absent during expiration.

Pathological changes:

Wide split: A split is said to be wide when the split is heard during both inspiration and expiration.
Which means early A2 and delayed P2. It is seen in Mitral Regurgitation.

Narrow split: A split is said to be narrow, when no split is heard during inspiration.
Which means early P2 and delayed A2. It is seen in Aortic stenosis.

Paradoxical split: Sometimes, there is so much delay, that A2 occurs after P2, which is then known as Reverse or Paradoxical Split. Then the question arises how to know the reversal of the components? How to differentiate A2 from P2
Answer - Split which is heard in expiration and not in inspiration is paradoxical split!

Fixed split: Seen in ASD. With an atrial septal defect (ASD), the right ventricle can be thought of as continuously overloaded because of the left to right shunt, producing a widely split S2. (P2 is delayed.... Always delayed!) Because the left and right atrium are linked via the defect, inspiration produces no net pressure change between them, and has no effect on the splitting of S2. Thus, S2 is split to the same degree during inspiration as expiration, and is said to be “fixed.”

Loud A2:
Atherosclerosis
Aneurysm of aorta
More pressure in Aorta (systemic hypertension)

Loud P2:
Pulmonary hypertension
Pulmonary artery dilation
(MS shows early loud P2)


That's all!  :)
The only way to master in auscultation is to auscultate.
Keep listening to your heart sounds
Stay awesome.

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