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Correspondence

Is the Analysis Over the Time Domain or Over the Frequency Domain Significant for the Detection of Bileaflet Mechanical Heart Valve Dysfunction?

^a Department of Chemical Process Engineering, University of Padova, via Marzolo 9, Padova, 35131 Italy
^b Department of Cardiovascular Surgery, University of Padua School of Medicine, via Giustiniani 2, Padova, 35128 Italy
^c Clinical Cardiology, Department of Cardiologic, Thoracic and Vascular Sciences, University of Padua School of Medicine, via Giustiniani 2, Padova, 35128 Italy

(Email: andrea.bagno{at}unipd.it).

To the Editor:

We are investigating the closing sounds of bi-leaflet mechanical heart valves (MHVs) for the early detection of valve dysfunction. Bi-leaflet MHVs are known to generate a typical "double click" due to the asynchronous closure of the leaflets. A simple phonographic analysis allows checking the presence of "double clicks" in a normally functioning MHV; if the signal, monitored over the time domain, lacks "double clicks" (or a sufficient number thereof), the hampered mobility of one leaflet can be hypothesised, thus suggesting further analyses because this event can be due to endothelial pannus growth, thromboembolic deposition on the occluder, or on the annular ring of the valve. This is the diagnostic approach of the Myotis 3C device (CardioSignal, GmbH, Germany) that acquires MHVs signals in the range of 0 to 22 kHz, filters out components below 10 kHz, and uses an embedded Fourier tra FFT-based algorithm to analyze signal profiles. The FFT is adequate when applied to stationary signals, but harmonic analysis does not represent the ideal approach in this case, because MHV signals are nonstationary. Thus, we improved the classification performances of the Myotis 3C device (CardioSignal) by implementing a time-frequency analysis as a more proper signal processing technique [1]. In particular, we used a continuous wavelet transform (CWT)-based algorithm, designed to verify the "double click" feature by means of the analysis of the CWT coefficients, instead of the sole analysis of the signal in the time domain.

The performances of a second device (ThromboCheck [CardioSignal GmbH]), also produced by the same manufacturer, were presented in an interesting article based on a multicentric study [2]. In this case, MHVs are classified by comparing the signal spectra, as calculated by FFT, even though the analytical procedure is not fully described in the text. Actually, Figure 2 is quite misleading; Figures 2A and 2B simply depict the signals profiles as monitored over the time domain; they allow checking the presence of "double clicks" and do not show the "frequency analysis of (A) a normal bi-leaflet valve and (B) immediately after first thrombotic deposits," as declared in the caption. Moreover, Figure 2C illustrates the FFT spectra of a "normal" valve and a "thrombosed" valve; it is likely to see that the spectra are dissimilar, but this finding has to be supported by specific classification criteria to give explanation for the differences.

We would like to suggest an open discussion about the informative content that can be extracted from the frequency spectra of phono-cardiographic signals, in particular which information can be obtained from the frequency analysis. Is it correct to consider the overall 0 to 20 kHz range, without filtering out signal components below 10 kHz (ie, breathing murmurs and native valve tones of the patient's heart)? Because most of the sound produced by a MHV falls above the 0 to 20 kHz range, it could be useful to analyze (and compare) the frequency spectra in the ultrasound region.

	References

Top References

 

1. Bagno A, Anzil F, Tarzia V, et al. Application of wavelet analysis to the phono-cardiographic signal of mechanical heart valve closing sounds Int J Artif Organs 2009(submitted for publication).
2. Fritzsche D, Eitz T, Laczkovics A, et al. Early detection of mechanical valve dysfunction using a new home monitoring device Ann Thorac Surg 2007;83:542-548.[Abstract/Free Full Text]

This article has been cited by other articles:

				S. Schenk and D. Fritzsche Reply. Ann. Thorac. Surg., March 1, 2009; 87(3): 987 - 988. [Full Text] [PDF]

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Tomaso Bottio Gino Gerosa Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Bagno, A. Articles by Pengo, V. Search for Related Content PubMed PubMed Citation Articles by Bagno, A. Articles by Pengo, V. Related Collections Valve disease Related Article