HEART SOUNDS: S1, S2, S3, S4 and Heart Murmurs by NJE

Heart sounds are generated by blood flowing in and out of the heart’s chambers through the valves as they open and close. The first indication of heart disease may be the discovery of an abnormal sound on auscultation. These include the aortic area, the pulmonary area, Erb’s point, the tricuspid area, and the apical area. Four heart sounds have been described. These are the first heart sound (S1), second heart sound (S2), third heart sound (S3), and fourth heart sound (S4). S1 and S2 are heard normally.

First Heart Sound S1

S1—First Heart Sound: Closure of the mitral and tricuspid valves creates the first heart sound (S1). It is heard best at the apex of the heart (apical area). First heart sound represents the beginning of systole. 

Causes of S1

S1 occurs due to vibration set up by:

1. Sudden closure of the AV valves.

2. Rapid increase in tension in the ventricular muscles during isometric contraction acting on filled ventricles.

3. Turbulence created in the blood due to ventricular contraction.

Characters of S1

It is a soft sound heard as ‘lub’.

Significance of S1

It signifies the beginning of ventricular systole and AV valve closure.

a. Accentuation of first heart sound occurs in:

− Exercise 

− Hyperkinetic circulatory states like anemia, beriberi 

− Hypertension

b. Diminution of first heart sound occurs in:

− Shock

− Acute myocardial infarction

− Constrictive pericarditis

− Pericardial effusion

− Cardiomyopathy (in the advanced stage)

− Obesity

− Emphysema 

Splitting of S1

First heart sound has two components: the mitral and the tricuspid components. 

1. The mitral valve closes slightly before the tricuspid valve. This gives rise to splitting of the first heart sound. 

2. But this splitting cannot be detected by auscultation, because both the components are very low-pitched and merge into each other. 

3. Therefore, splitting of the first heart sound is always considered as pathological.

Second Heart Sound S2

S2—Second Heart Sound. Closing of the aortic and pulmonic valves produces the second heart sound (S2).  S2 is heard loudest at the base of the heart. The aortic component of S2 is heard clearly in both the aortic and pulmonic areas, and less clearly at the apex.

Causes of S2

1. This occurs primarily due to closure of semilunar valves.

2. Rush of blood into the ventricles due to opening of the AV valves contributes.

Character of S2

This is heard as ‘dup’.

Significance of S2

Second heart sound signifies the end of clinical systole and closure of semilunar valves.

a. Loud A2 (aortic component) occurs in:

− Systemic hypertension

− Aortic dilatation

b. Diminished A2 occurs in:

− Aortic stenosis

− Aortic incompetence

c. Loud P2 (pulmonary component) occurs in:

− Pulmonary hypertension

− Pulmonary artery dilation

d. Diminished P2 occurs in:

− Pulmonary stenosis

Splitting of S2

Splitting of the second sound is due to the gap between the aortic and pulmonary components. It is easy to detect because sounds of aortic and pulmonary valve closure are high-pitched and can be separated. Splitting is most easily heard in children and may not be audible in elderly subjects. 

Mechanism of Splitting

The splitting of the second heart sound is due to the separation between the closure of aortic and pulmonary valves. 

1. The closure of pulmonary valve always follows the closure of aortic valve (aortic valve closes first). The splitting is distinctly heard during inspiration. 

2. During inspiration, more blood is drawn into the thorax. Therefore, venous return to right atrium increases and right ventricular stroke volume increases. This increases the duration of right ventricular systole. Thus, P2 is slightly delayed. 

3. Also, during inspiration, left ventricular stroke volume decreases because blood is pooled in the dilated pulmonary vessels and dilated left atrium, which occurs due to increased negative intrathoracic pressure. Therefore, left ventricular systole is shortened and A2 arrives earlier. 

4. Thus, during inspiration, A2 occurs earlier and P2 occurs later. Hence, splitting of the second sound widens during inspiration. 

5. Opposite mechanisms operate during expiration and splitting narrows.

Reverse Splitting

When pulmonary valve closes earlier to aortic valve closure, the condition is called reverse splitting. This occurs when the left ventricle takes more time to empty than the right ventricle. It is seen in left bundle branch block (LBBB) and in left ventricular failure.

Third Heart Sound S3

A gallop sound occurring during rapid ventricular filling is called a third heart sound (S3); it represents a normal finding in children and young adults. Such a sound is heard in patients who have the myocardial disease or in those who have HF and whose ventricles fail to eject all of their blood during systole. An S3 gallop is heard best with the patient lying on the left side. Third heart sound is usually not heard, though it is always prominently detected in phonocardiogram.  A third sound can arise from either side of the heart, but usually, it arises in the left ventricle.

Causes of S3

1. It is caused by the vibration set-up in the ventricle during the early period of rapid ventricular filling.

2. Rebound fencing of the cusp of the valve and chordae of the respective valve due to vigorous elongation of the ventricle caused by rapid inflow of blood.

Character of S3

It is best heard in the mitral area.

It follows the aortic component of the second sound and heard early in the diastole, i.e. just after the second sound.

Significance of S3

1. It is attributed to rapid ventricular filling and is found in relatively hyperkinetic circulation in young persons. It is heard in diseases in which the mitral diastolic flow is increased as occurs in mitral regurgitation and ventricular septal defect.

2. It is an important sign of heart failure due to any cause. In heart failure, the atrial pressure is increased and the early filling of the ventricle is rapid.

3. It may be heard shortly after myocardial infarction or in diseases where the distensibility of the ventricular muscle is altered. The sound arises from vibrations in the atrioventricular valve structures and in the ventricular muscle.

Fourth Heart Sound S4

Gallop sounds heard during atrial contraction is called fourth heart sounds (S4). An S4 is often heard when the ventricle is enlarged or hypertrophied and therefore resistant to filling. Such a circumstance may be associated with CAD, hypertension, or stenosis of the aortic valve. On rare occasions, all four heart sounds are heard within a single cardiac cycle, giving rise to what is called a quadruple rhythm. It is never heard in normal individuals. The presence of the fourth heart sound is always considered as abnormal.

Causes OF S4

1. It is caused by atrial contraction.

2. It is produced by the vibration set up within the ventricle due to the inflow of blood produced by atrial systole.

Character of S4

1. Low-pitched

2. Occurs just before the first sound, i.e. late in the diastole.

Significance of S4

1. It always indicates an increased stiffness or non-compliance of the ventricles. Therefore, when the bolus of blood is delivered into the ventricle by atrial contraction, it facilitates a sudden increase in ventricular pressure.

2. It is seen in left ventricular hypertrophy due to hypertension, myocardial infarction, pulmonary embolism, and pulmonary hypertension.

Triple Heart Sound

This consists of three heart sounds: the first and second heart sounds, and the third sound can be either the third or fourth heart sound. 

1. The triple rhythm associated with the normal heart rate may not be a serious one, but if it is present with a definite cardiac pathology, it may signify the seriousness of the condition. 

2. When the heart rate increases to more than 100 per minute, the triple rhythm is called gallop rhythm, because it produces a typical cadence of the gallop of a horse. 

Heart Murmurs 

Murmur occurs due to turbulence in the blood flow at or near a valve, or an abnormal communication within the heart. Murmurs differ from the heart sounds in the sense that these are of longer duration and higher frequency, whereas heart sounds have shorter duration and lower frequency. When a murmur is present, the following points are carefully noted.

Site of Origin: The area over which murmur is maximally heard is noted. The point of maximal intensity usually (but not always) indicates its site of origin.

Timing and duration: Depending on the timing of murmur, murmurs are classified into systolic, diastolic, or continuous. Depending on the duration, it may be early diastolic, mid-diastolic, early systolic, pan-systolic, etc.

Character: The murmur may be soft-blowing to harsh, rough, and rumbling. Loud and rough murmurs are usually associated with organic valvular and congenital lesions.

Radiation (Conduction): From the site of maximum intensity, auscultation is performed in different directions to detect whether the murmur is localized or conducted to other parts. Conduction is characteristic of some murmurs, e.g. the murmur of mitral stenosis is usually localized whereas the murmur of mitral incompetence selectively propagates towards the axilla.

Relation with respiration: During inspiration, the stroke volume of the right ventricle increases while that of the left ventricle decreases. Therefore, any murmur becoming louder during inspiration is considered to originate from the right ventricle, and any murmur increasing during expiration is attributed to originate from the left side of the heart.

Systolic murmurs

Ejection systolic murmurs are associated with ventricular outflow tract obstruction and occur in mid-systole with a crescendo–decrescendo pattern, reflecting the changing velocity of blood flow. pansystolic murmurs maintain a constant intensity and extend from the first heart sound throughout systole to the second heart sound, sometimes obscuring it. They occur when blood leaks from a ventricle into a low-pressure chamber at an even or constant velocity. Mitral regurgitation, tricuspid regurgitation and ventricular septal defect are the only causes of a pansystolic murmur. Late systolic murmurs are unusual but may occur in mitral valve prolapse if the mitral regurgitation is confined to late systole, and hypertrophic obstructive cardiomyopathy if dynamic obstruction occurs late in systole.

Diastolic murmurs

These are due to accelerated or turbulent flow across the mitral or tricuspid valves. They are low-pitched noises that are often difficult to hear and should be evaluated with the bell of the stethoscope. A mid-diastolic murmur may be due to mitral stenosis (located at the apex and axilla), tricuspid stenosis (located at the left sternal edge), increased flow across the mitral valve (for example, the to-and-fro murmur of severe mitral regurgitation) or increased flow across the tricuspid valve (for example, a left-to-right shunt through a large atrial septal defect). Early diastolic murmurs have a soft, blowing quality with a decrescendo pattern and should be evaluated with the diaphragm of the stethoscope. They are due to regurgitation across the aortic or pulmonary valves and are best heard at the left sternal edge, with the patient sitting forwards in held expiration.