Additional heart sounds

Diastolic Accessory Sounds

Diastolic acoustic phenomena include the opening snap of atrioventricular valves and the third heart sound ($S_3$).

Normally, mitral valve leaflets open silently at the onset of diastole. However, in mitral stenosis, the leaflets fuse and become sclerotic, restricting their opening. The impact of the blood flow causes a sharp vibration of the tense tissues, generating an opening snap (Opening Snap). This is a high-pitched, specific "clicking" sound that follows shortly after the second heart sound ($S_2$). It is best captured with the stethoscope diaphragm at the cardiac apex and slightly medially to it. A similar but rarer phenomenon may also occur at the tricuspid valve (auscultated near the lower part of the sternum).

Third heart sound ($S_3$) has a completely different origin. It is a dull, low-frequency sound occurring approximately 0.15 seconds after the second heart sound due to vibrations of the ventricular myocardium during rapid passive filling with blood. To hear it, the bell of the stethoscope is used, and the patient is asked to lie on their left side. This sound may be physiological in children, adults under 35–40 years of age, and women in the third trimester of pregnancy. If it appears in individuals over 40, however, it is an alarming pathological sign indicating decreased myocardial contractility (e.g., in chronic heart failure) or ventricular volume overload due to valvular regurgitation.

Systolic Extratones and Clicks

Additional sounds may also appear during ventricular systole. They are divided into early ejection sounds and later clicks.

Early systolic sounds are auscultated immediately after the first heart sound ($S_1$). Their genesis is associated with the vibration of the aortic or pulmonary valve leaflets, as well as the vibration of the walls of these vessels (especially in cases of pathological dilatation). These are high-pitched, sharp clicking sounds. They should be sought with the stethoscope diaphragm at the areas of vascular projection: the second intercostal space to the right (aorta) and left (pulmonary artery) of the sternum.

Mesosystolic (late) clicks occur somewhat later—in the interval between the first and second heart sounds. The main cause of their appearance is mitral valve prolapse (MVP), in which the leaflets bulge excessively into the left atrial cavity. This anomaly occurs in approximately 5% of the adult population. The click in MVP is also a high-frequency extratone. It is frequently accompanied by a systolic murmur indicating the development of mitral regurgitation (valve incompetence).

Fourth Heart Sound and Gallop Rhythms

Fourth heart sound (Atrial Gallop, $S_4$) occurs at the very end of diastole (presystole), immediately preceding the first heart sound ($S_1$). Hemodynamically, it is caused by enhanced atrial contraction as the atria attempt to overcome increased ventricular resistance. Like the third heart sound, it is a dull, low-frequency sound. Normally, it is sometimes heard in professional athletes, elderly individuals without pathology, and in the presence of bradycardia. A pathological fourth heart sound indicates ventricular stiffness or hypertrophy (characteristic of hypertension, cardiomyopathies, aortic stenosis). It becomes more distinct when the P-Q interval is prolonged (delayed AV conduction).

When a pathological third or fourth heart sound combines with tachycardia, a specific triple gallop rhythm is formed, symbolizing severe myocardial damage. Depending on the timing of the accessory sound, gallops are divided into:

• Presystolic: caused by the fourth heart sound ($S_4$) (sound preceding $S_1$).
• Protodiastolic: caused by the third heart sound ($S_3$) (sound following $S_2$ in early diastole).

The gallop rhythm is auscultated parasternally (third to fourth intercostal space on the left) or at the cardiac apex.

Auscultation of Artificial Valves

In patients after valve replacement surgery, the auscultatory picture changes drastically. Biological prostheses sound softer, whereas mechanical (ball-and-cage) valves generate two high-frequency accessory sounds per cycle: a closing sound and an opening sound.

For instance, with a mechanical mitral valve prosthesis, the closing sound is loud and follows immediately after the first heart sound ($S_1$). The opening sound occurs at the beginning of diastole, immediately after the second heart sound ($S_2$). The acoustic profile of such a prosthesis closely resembles the auscultatory picture of severe mitral stenosis.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Hemodynamics and Auscultatory Findings in Mitral Stenosis
• Causes and Manifestations of Ventricular Volume Overload
• Mitral Valve Prolapse: Etiology and Complications
• Differential Diagnosis of Systolic Murmurs
• ECG Signs of Atrioventricular Conduction Disturbance (P-Q Interval)

Other topics in the "Cardiovascular system" section

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