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Echophonocardiographic study of the initial low frequency component of the first heart sound
Insights
The initial low-frequency component of the first heart sound originates from left ventricular contraction and blood flow deceleration, not atrial contraction or mitral valve tension.
Area of Science:
- Cardiology
- Biomedical Engineering
- Physiology
Background:
- The genesis of the first heart sound, particularly its initial low-frequency component, remains incompletely understood.
- This component precedes high-frequency vibrations linked to atrioventricular valve closure.
Purpose of the Study:
- To investigate the origin of the low-frequency component of the first heart sound.
- To determine the role of left ventricular contraction and mitral valve dynamics in its production.
Main Methods:
- Echophonocardiograms were recorded from 36 individuals (10 normal, 26 with heart disease).
- Electrocardiograms (ECG) were used to assess cardiac rhythm (normal sinus rhythm, atrial fibrillation, atrioventricular block, atrial flutter).
- Apexcardiograms were obtained in some patients.
Main Results:
- The low-frequency component followed the QRS complex and preceded high-frequency vibrations.
- It coincided with the onset of rapid mitral valve closure on echocardiography.
- Its intensity varied with arrhythmias, being loudest after short RR intervals or with closely timed atrial systole.
- In patients with apexcardiograms, it aligned with the onset of ventricular systole.
Conclusions:
- The low-frequency component of the first heart sound is generated by left ventricular contraction and deceleration of antegrade mitral blood flow.
- Atrial contraction and mitral valve tension are not essential for this initial sound component.
Abstract:
To investigate the genesis of the initial low frequency component of the first heart sound that precedes the high frequency vibrations associated with closure of the atrioventricular valves, echophonocardiograms of 36 persons were recorded. These included 10 normal subjects and 26 patients with various types of heart disease including mitral valve replacement. Electrocardiograms demonstrated normal sinus rhythm in 23 subjects, atrial fibrillation in 9, complete atrioventricular block in 2 and atrial flutter in 2. In the phonocardiogram, the low frequency component of the first heart sound followed the onset of the QRS complex and preceded the first high frequency component of this sound. The low frequency component occurred simultaneously with the beginning of the final fast closing movement of the mitral valve on the echocardiogram and was found both in normal rhythm and in arrhythmias. However, in arrhythmias its intensity varied on a beat to beat basis, being loudest after a short RR interval or when atrial systole occurred very close to the expected time of ventricular systole. In patients in whom apexcardiograms were recorded, the low frequency component was coincident with or very close to the onset of ventricular systole. It is concluded that the low frequency component of the first heart sound represents vibrations caused by contraction of the left ventricle and deceleration of antegrade blood flow across the mitral valve. Neither atrial contraction nor mitral valve tension is necessary for the production of this soft initial component.