Detection of the Third Heart Sound Based on Nonlinear Signal Decomposition and Time–Frequency Localization

This study presents a precise way to detect the third (
$S_{3}$
) heart sound, which is recognized as an important indication of heart failure, based on nonlinear single decomposition and time–frequency localization. The detection of the
$S_{3}$
is obscured due to its significantly low energy and frequency. Even more, the detected
$S_{3}$
may be misunderstood as an abnormal second heart sound with a fixed split, which was not addressed in the literature. To detect such
$S_{3}$
, the Hilbert vibration decomposition method is applied to decompose the heart sound into a certain number of subcomponents while intactly preserving the phase information. Thus, the time information of all of the decomposed components are unchanged, which further expedites the identification and localization of any module/section of a signal properly. Next, the proposed localization step is applied to the decomposed subcomponents by using smoothed pseudo Wigner–Ville distribution followed by the reassignment method. Finally, based on the positional information, the
$S_{3}$
is distinguished and confirmed by measuring time delays between the
$S_{2}$
and
$S_{3}$
. In total, 82 sets of cardiac cycles collected from different databases including Texas Heart Institute database are examined for evaluation of the proposed method. The result analysis shows that the proposed method can detect the
$S_{3}$
correctly, even when the normalized temporal energy of
$S_{3}$
is larger than 0.16, and the frequency of those is larger than 34 Hz. In a performance analysis, the proposed method demonstrates that the accuracy rate of
$S_{3}$
detection is as high as 93.9%, which is significantly higher compared with the other methods. Such findings prove the robustness of the proposed idea for detecting substantially low-energized
$S_{3}$
.