Basics of Heart Sounds – S1 and S2 heart sounds
There are 2 main heart sounds that can be heard during auscultation: S1 and S2, also affectionately known as ‘lub’ and ‘dub’ respectively.
The S1 and S2 heart sounds are part of the normal heart sounds. Source: University of Michigan Murmur library
S1 heart sound 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 heart sound 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 the S1 and S2 heart sounds. 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 heart sounds
Ejection systolic click
Causes:
Ejection systolic click with ejection systolic murmur. Source: University of Michigan Murmur library
Mid-systolic click
Cause of mid-systolic click: Mitral valve prolapse
Mid-systolic click. Source: University of Michigan Murmur library
Opening snap
Causes of opening snap:
Opening snap with mid-diastolic murmur. Source: University of Michigan Murmur library
S3 and S4 heart sounds
S3 and S4 are extra heart sounds arising after S2.
The S3 heart sound 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
S3 heart sound. Source: University of Michigan Murmur library
The S4 heart sound 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
S4 heart sound. Source: University of Michigan Murmur library
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 heart sound
Causes:
Loud A2 heart sound
Cause: Systemic hypertension
Loud P2 heart sound
Causes:
- Pulmonary hypertension
- Atrial septal defect
Pathological Changes in S2 heart sound splitting
Wide-splitting S2 heart sound – splitting increases with inspiration:
Causes:
- Right bundle branch block
- Pulmonary stenosis
- Mitral regurgitation
- Ventricular septal defect
Fixed splitting S2 heart sound – splitting not affected by breathing:
Cause: Atrial septal defect
Reversed splitting S2 heart sound – splitting decreases with inspiration (so much so that it can lead to P2 arising before A2):
Causes:
- Left bundle branch block
- Aortic stenosis
- Coarctation of the aorta
- Patent ductus arteriosus
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