EVALUATION OF T-WAVE MORPHOLOGY IN
HIGH – RESOLUTION ECG MAPPING

M. Fereniec¹, M. Kacprzak¹, G. Karpinski², R. Maniewski¹, G. Opolski², D. Ircha^1
1Institute of Biocybernetics and Biomedical Engineering PAS
Trojdena 4, 02-109 Warsaw, Poland
² Chair and Department of  Internal Medicine and Cardiology, Central Teaching Hospital,
Banacha 1a, 02-297 Warsaw, Poland

Abstract: Spatial distribution of repolarization interval in ECG were studied using the 64-channel high-resolution body surface potential mapping. A parameter sensitive to T-wave shape changes is proposed basing on length of T-wave curve and integral of ECG amplitude  in T-wave period. The preliminary results obtained from the analysis of a limited number of normal subjects and post-infraction patients with heart insufficiency showed an interesting possibility for T-wave morphology evaluation using this  parameter.

INTRODUCTION

The non-invasive assessment of the cardiac repolarization heterogeneity is of clinical importance. It is generally accepted that the repolarization inhomogeneity  facilitates the re-entry phenomena causing the development of life-threatening ventricular arrhythmias, e.g. ventricular tachycardia [1- 4]. This concerns, in particular, a large group of post myocardial infarction patients and patients with left ventricular hypertrophy [2,5]. To evaluate the repolarization abnormalities the assessment of T-wave morphology has been proposed. The results of the shape analysis are less dependent on the T-wave timing which is very uncertain in some cardiac pathology.

The purpose of this study was to investigate the spatial changes of the repolarization period, in particular, T-wave in a high-resolution ECG recording. We have tested the reproducibility of some time and amplitude parameters of T-wave around the thorax, and we finally found the shape indices to be more effective for the analysis of the repolarization period.

A parameter sensitive for T-wave shape changes is proposed basing on length of T-wave curve and integral of ECG amplitude  in T-wave period. The preliminary results obtained from the analysis of a limited number of normal subjects and post-infraction patients with cardiac insufficiency showed an interesting possibility for T-wave morphology evaluation using this parameter.

METHODS

The examination was carried out in the electrically shielded room using the high-resolution ECG measurement system.

The system consists of 64 low noise amplifiers with 16-bit A/D converters (BIOSEMI, the Netherlands). Digital signals were transformed to the serial optical format and then were transferred to the computer via an optical fiber.  The data acquisition was controlled by the LabView  measurement software. To improve the signal-to-noise ratio the cross-correlation averaging and filtering methods were applied to 64 signals obtained from the lead  position on the torso according to the University of Amsterdam lead system [6]. High resolution ECG analysis of T-wave morphology is based on the parameter, which we refer as the T-wave Shape Index (TSI), defined as follows:

                

The parameter is a ratio of the  integral  of ECG amplitudes in the T-wave period and the total length of the T-wave curve. In the analysis the normalized TSI parameter is used.

RESULTS

The preliminary analysis of HR-ECG  in the  repolarization period was carried out on the set of data of 10 normal subjects and  10 post-infarction patients. The proposed TSI parameter was calculated for all 64 ECG signals of each subject and presented as  iso-amplitude maps.  The  TSI maps of patients show a large variability of TSI parameter, which can not be seen in any of the TSI maps of normal subjects.

The obtained results show also differences between TSI values for  normal subjects and post-infarction patients studied. In Fig. 1 the results obtained for the one patient after anterolateral and inferior infarctions are compared with the averaged (± SD) TSI of the normal group. Also presented maps clearly show the differences in  T-wave shape variations between normal subjects (Fig. 2) and  mentioned above patient (Fig. 3).

Figure 1. Comparison of  the averaged TSI value (mean ± SD) for normal group and the patient after anterolateral and inferior infarctions.

Figure 2. The averaged TSI map of 10 normal subjects.

Figure 3. The TSI map of the patient after anterolateral and inferior infarctions.

DISCUSSION

Different parameters of repolarization phase assessment were introduced [3,7] and it is well established that local changes of repolarization in the myocardium increase the risk for ventricular arrhytmia vulnerability [2,3]. QT dispersion is the most often proposed parameter of repolarization inhomogeneity assessment, but the exact measurement of QT interval is practically difficult [8]. The TSI parameter was calculated for averaged beats in all 64 location on the thorax.. the proposed TSI parameter is not depended on the accuracy of T-wave on- and offset detections. Only amplitude changes in the same time interval  established time interval for all leads  were taken into account.

It was observed that spatial heterogeneity of TSI parameter value is larger  in examined  patients with cardiac insufficiency then in normal subjects.

Obtained results indicate  that spatial variability of  TSI parameter might be a good marker of  variability of T-wave morphology and could reflect spatial repolarization gradient.

Acknowledgments: The authors thank Mrs A. Zbiec for her assistance in data measurements.

REFERENCES

[1] C.S. Kuo, K.  Munakata, C.P. Reddy,  B. Surawicz, „Characteristics and possible mechanism of ventricular arrhythmia dependent on the dispersion of action potential durations”, Circulation 1983; 67: 1356-67.

[2] A.D Corlan, L. Ambroggi, „New quantitative methods of ventricular repolarization analysis in patients with left ventricular hypertrophy”, Ital Heart J Vol August 2000; 542:48.

[3] Gy. Sandor, Gy. Kozmann, “Methods for Assessement of Ventricular Repolarization: a Model Study”, in Proceedings of Computers in Cardiology 2000.

[4] M. Tysler, M. Turzova, V. Szathmary, „Assessment of Heart Repolarization Properties from Body Surface Potentials Maps”, Measurement Science Review, Vol. 1, No. 1, 2001; 23-26.

[5] Y. Gang, K. Hnatkova, X. Guo, V. Batchvarov, A. Burak, W.J. McKenna, M. Malik, „Reproducibility of T wave morphology assessment in patients with hypertrophic cardiomyopathy and in healthy subject”, in Proceedings Computers in Cardiology 2001;28:393-396.

[6]  M. Fereniec, M. Kacprzak, R. Maniewski, A. Zbiec, D. Ircha, „The 64 channel system for high resolution ECG mapping”, in Proceedings of Computers in Cardiology 2001;28:513-515.

[7]  F.E. Smith, P. Langley , U. Steihoff, L. Trahms, J.P. Bourke, A. Murray, “Relation between Spatial Properties of Repolarization Interval And T-Wave Amplitude Using Magnetocardiography”, in Proceedings of Computers in Cardiology 2001;28:629-632.

[8] J.A. Kors, G. van Herpen, „Measurement error as a source of QT dispersion: a computerized analysis“, Heart 1998;80:453-458.