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Haemodynamic and sound events preceding first heart sound in mitral stenosis.

Phonocardiograms showed crescendo vibrations preceding Ml in 23 patients with mitral stenosis and atrial fibrillation. In the I5 patients subjected to cardiac catheterization, simultaneous left atrial and left ventricular pressure tracings revealed that the vibrations occurred during the preisovolumic phase of left ventricular systole and that there was a synchronous rise in the left atrial pressure during this period. An attempt is made to describe and explain the haemodynamic and sound events which precede the first major component (Ml) of the first sound in mitral stenosis. Before the onset of left ventricular contraction, a mitral diastolic murmur results essentially from the pressure gradientfrom the left atrium to left ventricle. With sinus rhythm this gradient is increased by atrial systole and there is then an increase in both the velocity and the volume offlow through the stenosed valve orifice. With the onset of the preisovolumic phase of left ventricular systole, the pressure gradient decreases and it is abolished at the end of this period when the left ventricular and atrial pressures cross and the mitral valve orifice is 'closed'. Irrespective of whether the left atrium has contracted or is fibrillating, the crescendo vibrations which occur during the preisovolumic phase result essentially from a progressive diminution in the valve orifice size which in turn causes an increase in velocity, but decrease in volume, offlow until the point of valve closure.