Heart Sounds and Extra Sounds

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Chapter 11 Heart Sounds and Extra Sounds

B. Cardiac Auscultation: Some Suggestions

C. Normal Heart Sounds

(1) First Heart Sound (S1)

11 Which factors are responsible for the loudness of S1?

In addition to shape and thickness of the chest wall, three major factors play a role:

1. The rate of rise in left ventricular pressure: This is a function of ventricular contractility, with stronger contractions causing a faster rise in left ventricular pressure and thus brisker and more forceful A-V closure. Hence, a loud S1 is typical of the hyperkinetic heart syndrome, whereas a soft (muffled) S1 is instead common in congestive heart failure, whose failing ventricles can only generate a slow rise in systolic pressure.

2. The separation between atrioventricular leaflets at the onset of ventricular systole: The closer the leaflets, the softer S1 is; conversely, the wider apart the leaflets, the louder S1 is. This mechanism feeds into two other important variables:

3. The thickness of the atrioventricular leaflet: The thicker the leaflets, the louder S1 is (banging hardbacks against each other generates more noise than banging paperbacks). Still, a soft S1 may indicate leaflets that are too rigid. Hence, a thickened and stenotic mitral valve may generate a booming S1 early on in the disease, but a softer (or absent) S1 when the leaflets get eventually calcified and fixed.

13 Which diseases present with a variable intensity of S1?

Heart blocks, such as second degree (i.e., Mobitz I or Wenckebach) and third degree:

Table 11-1 Intensity of S1

Loud Variable Soft
Short P-R interval (<160   msec) Atrial fibrillation Long P-R interval (>200   msec)
Increased contractility (hyperkinetic states) Atrioventricular block (Wenckebach and third degree) Decreased contractility (left ventricular dysfunction)
Thickening of mitral (or tricuspid) leaflets Ventricular tachycardia (due to atrioventricular dissociation) Left bundle branch block
Increased atrioventricular pressure gradient (stenosis of the A-V valves) Pulsus alternans Calcification of A-V valve(s)
Premature closure of mitral valve (acute aortic regurgitation)
Mitral (or tricuspid) regurgitation

(2) Second Heart Sound (S2)

45 What is the differential diagnosis of a fixed splitting of S2?

A late-systolic click (which precedes S2) and an early diastolic extra sound (which follows S2):

image The late-systolic click varies with bedside maneuvers and is loudest at the apex (conversely, the split S2 is unchanged with maneuvers and only heard at the base).

image The two most common early diastolic extra sounds are the S3 and the opening snap (OS) of mitral (or tricuspid) stenosis (for a discussion of how to differentiate an opening snap from a widely split S2 or an S3, see questions 103, 104, and 130). OS is primarily apical, whereas the split S2 is basilar. Still, OS can be loud enough to transmit to the base, thus producing a triple lilt in inspiration (OS + split S2, with a loud P2 because of pulmonary hypertension). Note that the interval between S2 and OS is wider than that between the two components of S2. Finally, an OS is usually (but not necessarily) associated with a diastolic rumble.