Changes in heart sounds

Fluctuations in the intensity of the first heart sound

In certain clinical situations, the loudness of the first heart sound is not constant, varying from one cardiac cycle to another. The sound may seem sometimes "booming" and at other times completely muffled.

Such changes result from rhythm and conduction disorders:

• Atrial fibrillation. Due to the chaotic rhythm, diastolic pauses vary in duration. This leads to uneven ventricular filling. The varying degree of filling directly affects the contraction force and, consequently, the amplitude (loudness) of the resulting sound.
• Complete atrioventricular block. In this pathology, dissociation of contractions occurs (atria and ventricles work independently). Periodically, their contractions coincide, causing a phenomenon of sharp loudness fluctuation — the so-called Strazhesko's "cannon" sound.

Changes in the loudness of the second heart sound

Auscultation of the second (diastolic) sound is traditionally performed at the base of the heart, i.e., in the second intercostal space to the left and right of the sternum.

1. General weakening of the second heart sound

The weakening of sound over all points at the base of the heart can be associated with two groups of causes:

• Hemodynamic: decreased pressure in the major great vessels and reduced blood filling.
• Valvular: structural damage to the aortic valve cusps or pulmonary valve, which impairs their tight closure and full slamming shut.

2. Enhancement of the second heart sound (Accentuation)

Accentuation is a condition where the second heart sound sounds significantly more intense on one side of the sternum compared to the symmetrical point on the other side. The main mechanism of this phenomenon is an increase in blood pressure in the corresponding great vessel, which causes the valves to slam shut faster and louder.

Topical diagnosis of accentuations:

1. Accentuation over the aorta (auscultated in the 2nd intercostal space on the right). Occurs in arterial hypertension (the most frequent cause) or marked aortic sclerosis (when decreased elasticity of the vessel wall resonates and amplifies the sound).
2. Accentuation over the pulmonary trunk (auscultated in the 2nd intercostal space on the left). Indicates increased pressure in the pulmonary circulation. It is found in mitral valve defects and the development of "cor pulmonale".

Local weakening of the second heart sound

Sometimes the second heart sound weakens not everywhere, but only at one specific auscultation point. This indicates an isolated lesion:

• Over the aorta: observed in calcinosis (deposition of calcium salts in the cusps). The valves become rigid and immobile, and the sound of their closure is muffled.
• Over the pulmonary trunk: characteristic of pulmonary valve stenosis.

Note: The weakening of sound over the pulmonary trunk may also have an extracardiac cause. For example, the sound is poorly conducted due to a thick chest wall (in pronounced obesity or heavily developed musculature).

Weakening of both heart sounds (S1 and S2)

If the physician notes the muffling of both heart sounds simultaneously, this is an alarming sign of pathology of the heart muscle itself.

Mechanism of pathology: Pronounced diffuse myocardial injury of the ventricles leads to a sharp decrease in its contractility. A weakened muscle cannot generate a resonant sound.

Clinical examples:

• Myocarditis (inflammation of the heart muscle).
• Myocardial dystrophies (metabolic disorders in the myocardium).
• Coronary artery disease (CAD).

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Mechanism of normal S1 and S2 generation
• Rules and points of cardiac auscultation
• Pathophysiology of cor pulmonale
• Auscultatory pattern of mitral valve defects

Other topics in the "Cardiovascular system" section

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