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


CONCLUSIONS
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.
Hunt
Anthony C
AC
Cardio-Analytics, ITTC 2, Tamar Science Park, Davy Road, Derriford, Plymouth, UK PL6 8BX. tony.hunt@talk21.com
D001145:Arrhythmias, Cardiac / Q000503:physiopathology* / Q000628:therapy; D002303:Cardiac Output, Low / Q000209:etiology / Q000503:physiopathology*; D017147:Defibrillators, Implantable; D004562:Electrocardiography; D006801:Humans; D009203:Myocardial Infarction / Q000150:complications* / Q000503:physiopathology; D017202:Myocardial Ischemia / Q000503:physiopathology; D010865:Pilot Projects