SN1
SHORT NOTE
5M
★ High-yield
Enumerate the heart sounds. Give their causes, characteristics and areas of auscultation.
Introduction
Heart sounds = the sounds produced by the closure of the cardiac valves and the associated turbulence, heard with a stethoscope over the praecordium.
The Four Heart Sounds
| Sound | Cause | Duration | Pitch | Coincides with |
|---|---|---|---|---|
| First (S1) — "LUBB" | Closure of mitral and tricuspid valves | 0.15 s | Low (25–45 Hz) | Onset of ventricular systole; apex beat; carotid pulse |
| Second (S2) — "DUPP" | Closure of aortic and pulmonary valves | 0.12 s | High (50 Hz) | End of systole (protodiastole) |
| Third (S3) | Rapid ventricular filling | 0.1 s | Very low | Early diastole |
| Fourth (S4) | Atrial systole | 0.02–0.04 s | Very low | Late diastole |
Areas of Auscultation
| Valve | Area |
|---|---|
| Mitral | Apex — 5th left intercostal space, mid-clavicular line |
| Tricuspid | Left sternal border, 4th–5th space |
| Aortic | 2nd right intercostal space |
| Pulmonary | 2nd left intercostal space |
Splitting of the Second Sound
- Physiological splitting — on inspiration; ↑ venous return delays pulmonary valve closure (A2 before P2)
- Wide fixed splitting → atrial septal defect
- Reversed (paradoxical) splitting → left bundle branch block, aortic stenosis
Methods of Recording
- Phonocardiography — graphic record of heart sounds, used to time them against the ECG
- S1 coincides with the R wave of the ECG and the upstroke of the carotid pulse
- S2 coincides with the end of the T wave
Applied Aspects
- S3 — normal in children and young adults; pathological after 40, indicating ventricular failure or volume overload → gallop rhythm
- S4 — always pathological in adults; indicates a stiff, non-compliant ventricle (hypertension, aortic stenosis). Absent in atrial fibrillation
- Loud S1 — mitral stenosis; soft S1 — mitral regurgitation, heart failure
- Murmurs — produced by turbulent flow through a narrowed (stenotic) or incompetent valve
All questions in Cardiovascular System
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