First heart sound. monday

1. FIRST HEART SOUND
Mechanism: S1 is caused by 4 components - 1. Atrial
2. Muscular
3. Valvular by mitral & tricuspid valves.
4. Vascular.
The component responsible predominantly for the first sound is the valvular component.
Intensity : of S1 depends on 1 .Position of mitral valve leaflets at the onset of ventricular systole.
2. Force of ventricular contraction.
3. Rate of rise of LV pressure pulse.
4. Presence or absence of structural disease of mitral valve.
5. Thickness of the valve.
S1 is louder if diastole is shortened because of tachycardia, if AV flow is increased because of high cardiac output, or
prolonged because of mitral Stenosis, or if atrial contraction precedes ventricular contraction by unusually short
interval reflected in a short PR interval.
Loud s1 in the presence of mitral stenosis usually signifies that the valve is pliable and it remains open at the onset of
isovolumetric contraction because of elevated left atrial pressure.
A soft s1 may be due to poor conduction of sound through chest wall, a slow rise of left ventricular pressure, long PR
interval or imperfect closure due to reduced valve substance as in mitral regurgitation.s1 is also soft when anterior
mitral leaflet is immobile because of rigidity and calcification, even in the presence of predominant mitral stenosis.
In the presence of a normal heart rate and absence of atrial fibrillation, when you encounter a loud first sound, mitral
Stenosis is to be looked for.
Duration: - 0.15 seconds & 25 to 45 Hz frequency. It is a low pitched sound.

SOFT S1
↓cardiac output ↑PR interval Obesity MR TR & acute AR
Calcified AV valves.
LOUD S1
↑cardiac output Tachycardia Short PR interval
Mitral Stenosis (↑LA pressure) Thin chest wall Atrial myxoma-rare.
VARIABLE S1
Atrial Fibrillation Complete heart block Extra systoles.
SPLIT S1
RBBB with PHT LV pacing LV Ectopic Beats Ebsteins anomaly.
REVERSE SPLIT S1
RV pacing, Ectopics & idioventricular Rhythms from RV.

2. References: Macleod’s, Hutchinson’s, Ganong, The Hurst, AHA Cardiac examination, Samuel oram. By Dr M.Abdul Khadir.