Overview
This lecture explains the origins, timing, and significance of the four main heart sounds (S1, S2, S3, S4), their relation to the cardiac cycle, and their clinical interpretations.
Cardiac Cycle and Heart Sounds
- Heart sounds are labeled S1, S2, S3, and S4.
- The gap between S1 and S2 is systole (heart contracts); gap between S2 and S1 is diastole (heart relaxes).
- S1 occurs when tricuspid and mitral valves close, marking the beginning of systole.
- S2 is produced by closure of pulmonary and aortic valves, marking the start of diastole.
Characteristics and Causes of Heart Sounds
- S1 sounds like “lub”; S2 sounds like “dub.”
- S3 occurs just after S2 during early diastole, associated with rapid ventricular filling.
- S4 occurs just before S1 in late diastole, linked with atrial contraction into stiff ventricles.
Clinical Significance of S3 and S4
- S3 is a low-frequency sound (“ventricular gallop”), heard best at the apex with the bell of the stethoscope.
- Physiological S3 can be normal in children and adults under 30.
- Pathological S3 found in conditions like cardiomyopathy, aortic/mitral regurgitation, and constrictive pericarditis.
- S4 (“atrial gallop”) is heard in late diastole at the apex; always abnormal.
- S4 indicates stiff (non-compliant) ventricles, seen in hypertrophic cardiomyopathy and systemic hypertension.
Key Terms & Definitions
- Systole — period when the heart contracts, between S1 and S2.
- Diastole — period when the heart relaxes, between S2 and S1.
- S1 — first heart sound, caused by closure of tricuspid and mitral valves.
- S2 — second heart sound, caused by closure of pulmonary and aortic valves.
- S3 — third heart sound, due to rapid ventricular filling; normal in youth, pathological in adults.
- S4 — fourth heart sound, caused by atrial contraction into stiff ventricles; always pathological.
- Ventricular gallop — extra heart sound (S3) linked to rapid filling of the ventricle.
- Atrial gallop — extra heart sound (S4) due to atrial contraction against non-compliant ventricles.
- Diastolic dysfunction — impaired relaxation of the ventricles leading to S4.
Action Items / Next Steps
- Review anatomical locations for auscultating each heart sound.
- Study heart sound timing within the cardiac cycle, especially for S3 and S4.
- Read about clinical conditions associated with abnormal S3 and S4 sounds.