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T Wave Alternans in high arrhythmic risk patients: analysis in time and frequency domains: a pilot study.

Hunt AC - BMC Cardiovasc Disord (2002)

Bottom Line: Time domain, resultant absolute difference vectors (ATA), were calculated for alternate resultant T wave sequences.Cross spectral analysis showed no significant differences in group ATA frequency content.The frequency content and microvolt magnitude of T wave alternans was not significantly different in these two groups.

View Article: PubMed Central - HTML - PubMed

Affiliation: Cardio-Analytics, ITTC 2, Tamar Science Park, Davy Road, Derriford, Plymouth, UK PL6 8BX. tony.hunt@talk21.com

ABSTRACT

Background: T wave alternans (TA) is a repolarisation phenomenon manifesting as a microvolt beat to beat change in the amplitude of the T wave and ST segment. TA has been shown to be a predictor of arrhythmic risk in unselected myocardial infarction populations. TA has not been used to differentiate risk within the ischaemic cardiomyopathy population.

Methods: The subjects investigated comprised, Group 1: 7 stable patients with remote (>20 months) extensive myocardial scarring and no arrhythmic events (NYHA 3 and 4). Group2: 9 post infarction patients with malignant arrhythmia and implantable defibrillator. During breath holding, 20 continuous QRST complexes from each patients X, Y and Z leads were digitally recorded. Time domain, resultant absolute difference vectors (ATA), were calculated for alternate resultant T wave sequences. Group differences between the magnitude and temporal distribution of mean ATAs and their spectral and cross-spectral analysis were compared.

Results: Group 1 v Group 2 mean ATAs were 10.7 (7.17) v 11.7 (8.48) respectively, not significant. Each group had a homogenous temporal distribution of ATAs. Both group's largest mean ATA frequency components were between 0 to 25 Hz, the largest ATA component being at the DC frequency. Cross spectral analysis showed no significant differences in group ATA frequency content.

Conclusion: The frequency content and microvolt magnitude of T wave alternans was not significantly different in these two groups. The specificity of T wave alternans for differentiating arrhythmic risk in post infarction scarring and heart failure needs investigation.

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Diagram showing methodology for sampling analog ECG signal in X, Y and Z leads in a rested, supine patient during breath holding. 400 milliseconds of alternate T wave sequences were ensemble averaged for each lead and collected in matrix bins represented by X1, Y1, Z1 and X2, Y2 and Z2.
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Figure 1: Diagram showing methodology for sampling analog ECG signal in X, Y and Z leads in a rested, supine patient during breath holding. 400 milliseconds of alternate T wave sequences were ensemble averaged for each lead and collected in matrix bins represented by X1, Y1, Z1 and X2, Y2 and Z2.

Mentions: For each lead on each patient, sequences of the alternate ST-T waves were ensemble averaged over a 400 millisecond duration using the positive or negative peak of the T wave as the fiducial central point of data collection over 400 milliseconds, see figure 1. In leads where the T wave was of low magnitude, the fiducial central point was taken to occur as the point at an average of the times from the peak QRS deflection to the fiducial T wave point in the other clearly demarcated orthogonal leads. The vectors of the squared magnitude of differences in ensemble averaged time aligned alternating ST-T sequences were calculated on each lead from each patient. For each patient, the resultant absolute difference vector (ATA) was calculated as the square root of the summed squared differences between alternate ensemble averaged T waves for each X, Y and Z vector. All calculations were performed using Mathcad Professional signal processing software on a Acer Pentium 2 PC. Comparisons were made between each mean group ATA as well as between the intra and inter-group means of vectors representing each third time interval of the respective mean ATAs. The spectral content was calculated for each group mean ATA by digital fast Fourier algorithm and cross spectral analysis was calculated between each group mean ATA to assess differences in the frequency components within each group. In order to assess group differences in the 80 to 500 Hertz frequency band, mean magnitude and standard deviation of the 80 to 500 Hz frequency band in the group with the smallest mean magnitude was considered noise and group differences between mean magnitudes in this band only considered significant if they exceeded three times the previously calculated standard deviation.


T Wave Alternans in high arrhythmic risk patients: analysis in time and frequency domains: a pilot study.

Hunt AC - BMC Cardiovasc Disord (2002)

Diagram showing methodology for sampling analog ECG signal in X, Y and Z leads in a rested, supine patient during breath holding. 400 milliseconds of alternate T wave sequences were ensemble averaged for each lead and collected in matrix bins represented by X1, Y1, Z1 and X2, Y2 and Z2.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC101381&req=5

Figure 1: Diagram showing methodology for sampling analog ECG signal in X, Y and Z leads in a rested, supine patient during breath holding. 400 milliseconds of alternate T wave sequences were ensemble averaged for each lead and collected in matrix bins represented by X1, Y1, Z1 and X2, Y2 and Z2.
Mentions: For each lead on each patient, sequences of the alternate ST-T waves were ensemble averaged over a 400 millisecond duration using the positive or negative peak of the T wave as the fiducial central point of data collection over 400 milliseconds, see figure 1. In leads where the T wave was of low magnitude, the fiducial central point was taken to occur as the point at an average of the times from the peak QRS deflection to the fiducial T wave point in the other clearly demarcated orthogonal leads. The vectors of the squared magnitude of differences in ensemble averaged time aligned alternating ST-T sequences were calculated on each lead from each patient. For each patient, the resultant absolute difference vector (ATA) was calculated as the square root of the summed squared differences between alternate ensemble averaged T waves for each X, Y and Z vector. All calculations were performed using Mathcad Professional signal processing software on a Acer Pentium 2 PC. Comparisons were made between each mean group ATA as well as between the intra and inter-group means of vectors representing each third time interval of the respective mean ATAs. The spectral content was calculated for each group mean ATA by digital fast Fourier algorithm and cross spectral analysis was calculated between each group mean ATA to assess differences in the frequency components within each group. In order to assess group differences in the 80 to 500 Hertz frequency band, mean magnitude and standard deviation of the 80 to 500 Hz frequency band in the group with the smallest mean magnitude was considered noise and group differences between mean magnitudes in this band only considered significant if they exceeded three times the previously calculated standard deviation.

Bottom Line: Time domain, resultant absolute difference vectors (ATA), were calculated for alternate resultant T wave sequences.Cross spectral analysis showed no significant differences in group ATA frequency content.The frequency content and microvolt magnitude of T wave alternans was not significantly different in these two groups.

View Article: PubMed Central - HTML - PubMed

Affiliation: Cardio-Analytics, ITTC 2, Tamar Science Park, Davy Road, Derriford, Plymouth, UK PL6 8BX. tony.hunt@talk21.com

ABSTRACT

Background: T wave alternans (TA) is a repolarisation phenomenon manifesting as a microvolt beat to beat change in the amplitude of the T wave and ST segment. TA has been shown to be a predictor of arrhythmic risk in unselected myocardial infarction populations. TA has not been used to differentiate risk within the ischaemic cardiomyopathy population.

Methods: The subjects investigated comprised, Group 1: 7 stable patients with remote (>20 months) extensive myocardial scarring and no arrhythmic events (NYHA 3 and 4). Group2: 9 post infarction patients with malignant arrhythmia and implantable defibrillator. During breath holding, 20 continuous QRST complexes from each patients X, Y and Z leads were digitally recorded. Time domain, resultant absolute difference vectors (ATA), were calculated for alternate resultant T wave sequences. Group differences between the magnitude and temporal distribution of mean ATAs and their spectral and cross-spectral analysis were compared.

Results: Group 1 v Group 2 mean ATAs were 10.7 (7.17) v 11.7 (8.48) respectively, not significant. Each group had a homogenous temporal distribution of ATAs. Both group's largest mean ATA frequency components were between 0 to 25 Hz, the largest ATA component being at the DC frequency. Cross spectral analysis showed no significant differences in group ATA frequency content.

Conclusion: The frequency content and microvolt magnitude of T wave alternans was not significantly different in these two groups. The specificity of T wave alternans for differentiating arrhythmic risk in post infarction scarring and heart failure needs investigation.

Show MeSH
Related in: MedlinePlus