Mechanism of loud first heart sound in mitral stenosis

Mechanism of loud first heart sound in mitral stenosis

In severe mitral stenosis, due to elevated left atrial pressure, the closure of the mitral valve is delayed and occurs at a time when the dp/dt of the ventricular pressure tracing is higher. The force of left ventricular contraction pushing back the mitral valve to the closed position will be higher at this stage. This enhances the intensity of the mitral component of first heart sound. The elevated left atrial pressure also keeps the mitral valve in a more open position at the onset of systole. This would mean a greater closing excursion of the mitral valve, increasing the intensity of the first heart sound.

Resonance of stiff non compliant mitral leaflets and chordae tendinae with increased amplitude may also contribute to the increased intensity of first heart sound in mitral stenosis [1]. Similar mechanisms have been invoked for the explanation of loud first heart sound in individuals with left atrial myxoma as well. In calcific mitral stenosis, the decreased mobility of the valve leaflets may decrease the intensity of the first heart sound.

Reference

  1. Joel M. Felner. Chapter 22. The First Heart Sound. Clinical Methods: The History, Physical, and Laboratory Examinations. 3rd edition. Walker HK, Hall WD, Hurst JW, editors. Boston: Butterworths; 1990.