R.H. Mitchell

University of Ulster, Aontroim, N Ireland, United Kingdom

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Publications (5)1.79 Total impact

  • R.H. Mitchell, O. Escalona
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    ABSTRACT: A novel and reliable approach which quantifies the degree of complexity of late potential (LP) activity in the time domain is presented. By defining the LP attractor in the microvoltage, 3-dimensional space, and then computing the fractal dimension (δ) of the attractor's trajectory, the degree of complexity of LP can be quantified with a single parameter. δ may indicate the chaotic behaviour of the terminal activity of the ventricular depolarisation process. The fractal dimension of the LP Attractor in post-MI subjects that are at risk is significantly higher than in post-MI subjects with low LP activity (p<0.001). δ may be considered as the criterion for discrimination. Fractal dimension analysis on LP is a novel diagnostic approach aimed at quantifying their complexity in the microvoltage 3-D space, and may be interpreted as a measure of their chaotic behaviour triggering a catastrophic arrhythmic episode
    Engineering in Medicine and Biology Society, 1998. Proceedings of the 20th Annual International Conference of the IEEE; 01/1998
  • O.J. Escalona, R.H. Mitchell
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    ABSTRACT: Frequency-domain analysis of ventricular late potentials in the three orthogonal leads XYZ can reveal features of clinical significance. However, a consistent and simple method of spectral analysis has not been agreed. For a more easy interpretation of the spectral information in the 3 orthogonal leads a novel method of vector spectral analysis of ventricular late potentials is proposed here. The method exploits the property of zero-phase normalisation in the N amplitude coefficients (real-valued) of the Discrete Hartley Transform (DHT). This property of the DHT allows an advantageous way of combining the three orthogonal spectra, SX, SY and SZ, into a vector magnitude spectrum, (SX<sup>2</sup>+SY<sup>2</sup>+SZ<sup>3</sup>)<sup>&frac12;</sup>. Summation of amplitude coefficients in the -300 to -60 Hz and 60 to 300 Hz frequency ranges in the DHT vector spectrum provided a simple clinical parameter, S. A clinical evaluation of S indicated that S is of significantly greater value (10.4±5.8 μV) in post-MI patients which are VT inducibles (at risk) than in healthy subjects (3.2±2.4 μV), p<0.001
    Engineering in Medicine and Biology Society, 1994. Engineering Advances: New Opportunities for Biomedical Engineers. Proceedings of the 16th Annual International Conference of the IEEE; 02/1994
  • O.J. Escalona, R.H. Mitchell
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    ABSTRACT: The presence of ventricular late potential (LP) activity in patients with post-myocardial infarction has been correlated with their susceptibility to develop ventricular tachycardia and may be used as a risk criterion. A reliable novel approach for characterising and detecting abnormal LP activity is presented. It consists of analyzing the degree of complexity of LP activity by quantifying their fractal dimension (δ). Fractal dimensional analysis was applied to the LP's attractor traced in the microvoltage, 3-dimensional space. The δ parameter may be interpreted as an index for the chaotic behaviour of the terminal activity of the ventricular depolarisation process which could trigger a catastrophic arrhythmic episode. Results of a clinical study indicated that the value of δ was significantly higher in at risk patients than in healthy subjects (p<0.001), and suggested that a value of δ>1.30 can be a risk criterion
    Computers in Cardiology 1993, Proceedings.; 10/1993
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    ABSTRACT: The process of QRS alignment as required in signal-averaged ECG can impose serious limitations on the spectral range of the signal output. This effect depends basically on the particular alignment technique being used and on the level and type of noise present in the recorded ECG. In clinical studies where a wide-band (1000 Hz) ECG averager is required, the conventional QRS alignment technique, based on maximum coherence matching (MCM) with a template beat, may not perform consistently well. An alternative QRS alignment technique based on the accurate detection of a single fiducial point (SFP) in the bandpass filtered (3-30 Hz) QRS complex was developed. Using computer simulation methods, a comparative assessment of the frequency bandwidths (3 dB points) offered by both MCM and SFP techniques as a function of noise level (15-100 muRMS) and type (EMG and 50 Hz interference), was carried out. The results of the comparative assessment indicated a better performance by the SFP technique in all cases of noise. Hence, the SFP technique would perform more reliably for high-frequency analysis of a noisy ECG, especially when 50 Hz interference is high. Furthermore, SFP is considerably faster than MCM (about four times) when implemented digitally, and its analogue realisation is feasible. The SFP technique is suitable for late-potential analysis in the signal-averaged ECG.
    Medical & Biological Engineering & Computing 08/1993; 31 Suppl:S137-46. · 1.79 Impact Factor
  • R.H. Mitchell, O.J. Escalona
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    ABSTRACT: First Page of the Article
    Engineering in Medicine and Biology Society, 1991. Vol.13: 1991., Proceedings of the Annual International Conference of the IEEE; 12/1991