The effect of cycle length on the time of occurrence of the first heart sound and the opening snap in mitral stenosis.

Phonocardiography is-often more valuable than electrocardiography in timing mechanical events in the cardiac cycle. This study shows that the opening and closing of the mitral valve are related to the length of the previous heart cycle as demonstrated by the variations occuring in aluricular fibrillation. These variations in valve action are controlled by the pressure gradient between left auricle and ventricle. T HE vibrations of the heart sounds are an immediate manifestation of various mechanical activities of the heart,. and, when suitably recorded, provide an excellent way of timing events which comprise the cardiac cycle. It is important, therefore, to recognize the effect of disease on the time of occurrence of these vibrations, their probable mode of production, and their relationship to other events in the cardiac cycle. It is agreed by most observers that the beginning of electrical activity in the heart muscle precedes mechanical activity as manifested by the vibrations of the first heart sound la, b, c; however, this discrepancy between mechanical and electrical events is more apparent than real. The spread of electrical activity in the myo-cardium occurs with extreme rapidity and, while mechanical contraction probably begins almost simultaneously,2 a short interval of time is required to produce a significant shortening of the muscle fibers. During this initial phase of ventricular systole, a few low intensity, low frequency vibrations occur (first component of the first heart sound3). These are followed by a group of large amplitude vibrations (second and third components), which comprise the main vibrations of the first heart sound. The beginning of these latter vibrations is generally ac-From the Cardiac Laboratory of the Massachusetts General Hospital. 576 cepted as being due to atrioventricular valve closure4 and time this event rather precisely. It is these large amplitude vibrations of the first heart sound, and therefore atrioventricular valve closure, which follow the beginning of electrical activity by an appreciable interval. The initial low frequency, low amplitude vibrations , which precede atrioventricular valve closure , may not be recorded if the technic is incorrect , or may be obscured by a diastolic murmur occurring during the presystolic interval. They occur, however, whether normal rhythm or auricular fibrillation is presents Luisada5 has recently pointed out that the interval between the beginning of the upstroke of the electrocardiographic R wave and the main vibrations of a simultaneously registered first heart sound may not be a constant one. The reason …