Analysis and study of the variation of splitting in the second heartbeat sound of wavelet transform

Abstract

The second heart sound, S2, consists of two acoustic components, A2 and P2. The former is due to the closure of the aortic valve and the latter is due to the closure of the pulmonary valve. The aortic valve usually closes before the pulmonary valve, introducing a time delay known as the 'split'. A technique based on discrete wavelet transform (DWT) and continuous wavelet transform (CWT) is developed in this paper to measure the split. To quantify splitting, two components in S2 (i.e. A2 and P2) are identified, and the delay between the two components can be estimated. One normal case and three pathological cases (mitral stenosis, pulmonary stenosis and atrial septal defect) are considered in this study. The split is measured for each S2 sound of the considered signals. The split normally varies in duration over the cardiac cycle. In certain pathologies such as ASD (atrial septal defect) or PS (pulmonary stenosis), the split becomes fixed over the cardiac cycle. The main part of this paper consists of the identification and measurement of the S2 split. The study confirms the notion of 'variable splitting' for normal phonocardiogram and 'fixed splitting' for ASD and PS cases. This paper relates also to the establishment of statistical parameters to make a distinction between normal and pathological cases of phonocardiogram signals.