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Heart Sounds – S1, S2 and Pathological Sounds

by | 26 Jan, 2021

Basics of Heart Sounds – S1 and S2

There are 2 main heart sounds that can be heard during auscultation: S1 and S2, also affectionately known as ‘lub’ and ‘dub’ respectively.

Normal heart sounds

Normal heart sounds. Source: University of Michigan Murmur library

S1 corresponds to the closing of the mitral and tricuspid valves during systole. During systole, ventricular pressure rises, leading to opening of the aortic and pulmonary valves as well as closure of the mitral and tricuspid valves.

S2 corresponds to the closing of the aortic and pulmonary valves at the beginning of diastole. S2 may be subdivided into aortic (A2) and pulmonary (P2) sounds as the aortic valve closes slightly before the pulmonary valve. The splitting between A2 and P2 can be exaggerated by inspiration, particularly in young individuals.

The pulse can be felt during systole between S1 and S2. This is particularly important for differentiating between systolic and diastolic murmurs (covered separately here), as well as identifying any pathological heart sounds.

Pathological Extra Heart Sounds – Clicks, Snaps, S3/S4

Ejection systolic click

Ejection systolic click
Ejection systolic click in aortic stenosis and pulmonary stenosis

Ejection systolic click with ejection systolic murmur. Source: University of Michigan Murmur library

Causes:

Mid-systolic click

Midsystolic click
Mid-systolic click in mitral valve prolapse

Midsystolic click. Source: University of Michigan Murmur library

Cause: Mitral valve prolapse

Opening snap

Opening snap
Opening snap seen in mitral stenosis and tricuspid stenosis

Opening snap with mid-diastolic murmur. Source: University of Michigan Murmur library

Causes:

S3 and S4

S3 S4
Pathological S3 and S4 heart sounds

S3 and S4 are extra heart sounds arising after S2.

 S3 heart sound. Source: University of Michigan Murmur library

S3 occurs during ventricular filling. It can be a normal finding in people aged 40 or under. Pathological causes are mostly related to heart failure and include:

  • Ischaemic heart disease
  • Dilated cardiomyopathy
  • Hypertrophic cardiomyopathy
  • Mitral regurgitation

S4 heart sound. Source: University of Michigan Murmur library

S4 arises when the atria contract against a stiff ventricle (such as in states of ventricular hypertrophy). Causes include:

  • Hypertension
  • Pulmonary hypertension
  • Aortic stenosis
  • Hypertrophic cardiomyopathy

Tumour plop

A rare diastolic heart sound classically associated with the movement of the tumour in atrial myxomas. 

Changes in Volume

The loudness of heart sounds can be altered by changes in the force of valve closure.

Loud S1

Causes:

Loud A2

Cause: Systemic hypertension

Loud P

Causes:

Pathological Changes in S2

Wide-splitting S2 – splitting increases with inspiration:

Wide splitting2
Wide-splitting of S2. Splitting increases with inspiration.

Causes:

Fixed splitting S2 – splitting not affected by breathing:

Fixed splitting2
Fixed splitting of S2. Splitting is not affected by inspiration.

Cause: Atrial septal defect

Reversed splitting S2 ­– splitting decreases with inspiration (so much so that it can lead to P2 arising before A2):

Reversed splitting
Reversed splitting of S2. Splitting decreases with inspiration (and can lead to P2 arising before A2).

Causes:

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