Paradoxical Splitting of the Second Heart Sound

Abstract

The second heart sound is caused by closure of the aortic-and pulmonary valves at the end of ventricular systole. Two components, from the separate closure of the two valves, are usually audible because of slight asynchrony of the two ventricles, aortic closure preceding pulmonary closure in normal subjects (Leatham and Towers, 1951). Potain (1866) observed that the character of the second heart sound altered with respiration. While it might be single during the expiratory phase of continued respiration it became clearly split with inspiration. Such a change in the second sound is found in most normal subjects and is due to prolongation of right ventricular systole during inspiration. This may be explained by the increased filling of the right atrium and ventricle from the great veins which takes place with the inspiratory fall in intra-thoracic pressure. No such change can occur on the left side of the heart since intrathoracic pressure changes affect the pulmonary veins and heart chambers equally. Sometimes a clearly split second heart sound becomes single or more closely split on inspiration (Fig. 1). Such paradoxical behaviour of the second sound with respiration is due to reversal of the normal order of valve closure, pulmonary closure preceding aortic closure (Leatham, 1952). This auscultatory sign may be recognized in the neighbourhood of the pulmonary area and confirmed by phonocardiography. A study has been made of 40 cases in which paradoxical splitting of the second heart sound was recognized on clinical and phonocardiographic examination.Method. The heart sounds were studied in simultaneous recordings taken from the pulmonary and mitral areas. The electrocardiogram and indirect carotid pulse were registered at the same time. High frequency records were used (Leatham, 1952) and measurements were made from the onset of the earliest high-frequency vibration recorded, tracings being made during held expiration. Additional phonocardiograms were made in the fourth or fifth left interspace close to the sternum in many cases to record splitting of the first heart sound, and records were taken during quiet respiration where possible. The aortic component of the second heart sound was identified in the records made at the pulmonary and mitral areas by its coincidence with the dicrotic notch of the carotid pulse (allowance being made for the delay in transmission of the arterial pulse to the carotid vessels). The pulmonary component was readily identified in records made at the pulmonary area but was absent from the mitral area records; it had no constant relation to the dicrotic notch. When splitting of the first heart sound was present the left-and right-sided components were identified where possible. These are probably caused by closure ofthe atrio-ventricular valves (Dock, 1933) and in normal subjects mitral closure is slightly before tricuspid. The tricuspid element is loudest at the left sternal edge in the fourth or fifth space and the mitral element at the apex. Confirmation of mitral closure was ob...

Determinants of Duration and Mean Rate of Ventricular Ejection

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Systolic Time Intervals and Heart Sounds in Left Bundle Branch Block

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Mechanisms of Fixed Splitting of the Second Heart Sound

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