Heart Sounds

HEART SOUNDS

Heart Sounds refer to the acoustic phenomena produced by the closure of cardiac valves and the resulting oscillations of blood and cardiac structures during the cardiac cycle. 

There are four heart sounds S1,S2,S3, & S4 which are typically produced, only the first two are usually audible with a stethoscope.

Electronic amplification can detect the less intense sounds S3 and S4, which can be recorded graphically as a phonocardiogram.

I. First Heart Sound (S1)

Cause: The first heart sound, described as "S1", is caused by the simultaneous closure of the atrioventricular (AV) valves (mitral and tricuspid). This closure results from the abrupt rise of ventricular pressure and the deceleration of blood flowing back towards the atria. It also involves oscillation of blood in the ventricular chambers and vibration of the chamber walls, as well as sudden tension and recoil of the AV valves.

• Timing: It occurs at the onset of ventricular systole, specifically during the isovolumetric contraction phase. It coincides with the R-wave of the ECG.

• Characteristics: S1 is typically prolonged (0.1–0.17 seconds), low-pitched (20–40 Hz), and has a booming quality. It is the loudest and longest of the heart sounds and has a crescendo-decrescendo quality.

Best Heard: Best heard over the mitral area (cardiac apex, typically the fifth intercostal space) and tricuspid area (just to the left of the lower sternum).

Physiological/Clinical Notes:

Intensity: The intensity of S1 is a function of the force of ventricular contraction and the distance between the valve leaflets. It is loudest when leaflets are farthest apart, such as when ventricular systole immediately follows atrial systole.

Splitting: While it is due to simultaneous closure, the mitral valve usually closes before the tricuspid valve, so S1 may be audibly "split".

II. Second Heart Sound (S2)

Cause: The second heart sound, described as "S2", is caused by the simultaneous closure of the semilunar valves (aortic and pulmonary valves). This closure results from the brief reversal of blood flow towards the ventricles at the end of ventricular ejection, which snaps the cusps together.

Timing: It occurs at the onset of isovolumetric ventricular relaxation. It coincides with the end of the T wave on the ECG.

Characteristics: S2 is typically shorter, abrupt, and clear, with a higher pitch than S1. It has a more snapping quality.

Best Heard: Best heard over the aortic area (second intercostal space to the right of the sternum) and pulmonary area (second intercostal space to the left of the sternum).

Physiological/Clinical Notes:

Intensity: Conditions causing more rapid closure of semilunar valves, like pulmonary or systemic hypertension, increase S2 intensity. In adults, the aortic valve sound is usually louder than the pulmonic sound.

Splitting: S2 can be split by inspiration, which delays the closure of the pulmonic valve. This is a normal phenomenon.

III. Third Heart Sound (S3)

Cause: S3 is associated with the rapid distension of the ventricles in early diastole. It is believed to result from vibrations of the ventricular walls caused by abrupt cessation of ventricular distention and deceleration of blood entering the ventricles.

Timing: Occurs in early diastole, during the rapid ventricular filling phase.

Characteristics: Consists of a few low-intensity, low-frequency vibrations.

Audibility: It may be audible in children with thin chest walls or in patients with left ventricular failure. In adults, its presence is often associated with disease.

Clinical Significance: A third heart sound in patients with heart disease is usually considered a grave sign. When accentuated (prominent and audible) along with S1 and S2, it can produce a triple rhythm or "gallop rhythm" (protodiastolic gallop).

IV. Fourth Heart Sound (S4)

Cause: S4 is caused by the oscillation of blood and cardiac chambers created by forceful atrial contraction.

Timing: Occurs in late diastole, just before ventricular contraction. It is associated with atrial systole.

Characteristics: Consists of a few low-frequency oscillations.

Audibility: Occasionally heard in normal individuals, but more typically heard during forceful atrial systole, especially in conditions like ventricular hypertrophy.

Clinical Significance: When accentuated (prominent and audible) along with S1 and S2, it can produce a triple rhythm or "gallop rhythm" (presystolic gallop).

General Notes on Heart Sounds:

Valve Opening: The opening of heart valves does not produce sounds; only their closure does.

Auscultation: Listening to heart sounds (auscultation) with a stethoscope is a key clinical method. Clinicians once "made a fine art" of detecting murmurs through auscultation to diagnose cardiac valvular disease.

Murmurs: Murmurs are abnormal heart sounds produced by abnormal patterns of blood flow (e.g., turbulence) in the heart. They are typically longer than heart sounds and have a "blowing" or "swishing" quality. Murmurs can be caused by diseased heart valves (e.g., stenosis or regurgitation) or increased blood flow (e.g., exercise).

Echocardiography: The movement of valve leaflets and their closure can be detected by echocardiography, which uses ultrasonic waves to visualize the heart and great vessels.