The first heart sound in left bundle branch block: an echophonocardiographic study
Circulation
|February 1, 1981
Summary
Left bundle branch block (LBBB) alters the timing of mitral and tricuspid valve closure, affecting the first heart sound. This study found delayed mitral closure and reduced first heart sound intensity in LBBB patients.
Area of Science:
- Cardiology
- Cardiac Electrophysiology
- Echocardiography
Background:
- The first heart sound originates from the closure of mitral and tricuspid valves.
- Left bundle branch block (LBBB) is known to affect cardiac electrical conduction and mechanical function.
Purpose of the Study:
- To investigate the impact of LBBB on the timing of mitral and tricuspid valve closure.
- To characterize the nature of the first heart sound in patients with LBBB.
Main Methods:
- Echophonocardiography, apexcardiograms, and systolic time intervals were used.
- 26 patients with LBBB were compared to 20 healthy subjects.
Main Results:
- LBBB caused variable delays in mitral valve closure, leading to normal, reversed, or simultaneous closure with the tricuspid valve.
- The interval from depolarization to mitral closure was significantly prolonged in LBBB patients (0.074s vs 0.057s).
- The first heart sound intensity was reduced in LBBB, with obscured mitral and tricuspid components.
Conclusions:
- LBBB disrupts normal valve sequencing and delays mitral closure due to altered ventricular activation.
- Delayed left ventricular contraction and increased isometric contraction time contribute to these findings.
- These electro-mechanical changes in LBBB directly impact the characteristics of the first heart sound.
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