QT dispersion(QTd) is a crude and approximate measure of abnormality of the complete course of cardiac repolarization. To overcome the methodological limitations of QTd, novel T-wave morphology variables, such as the complexity of the T wave assessed by principal component analysis (PCA), have been recently developed. To determine whether PCA can differentiate postMI(PMI) patients with malignant ventricular arrhythmias(VA) from without VA, 36 patients were studied : 12 PMI patients with VA, 12 age, sex and infarct-size matching PMI patients without VA and 12 healthy subjects were studied. Standard 12-lead ECGs were recorded digitally using the MAC-VU system (Marquette Medical Systems). QTcD was quantified as the difference between maximum and minimum QT intervals. T-wave loop morphology was quantified by the ratio of the second to first eigenvalues of the T-wave vector by PCA (PCA ratio). PCA parameters were computed using the QT Guard software package by Marquette. Results : PMI patients with VA(n =12) had increased PCA ratios compared with those without VA(44.3%짹31.5% vs 38.5%짹25.7%, P = 0.015). However, QTcD did not show the significant difference between groups(Table). Conclusion : Abnormalities of repolarization measured by PCA of the T-wave loop can detect the future arrhythmic events in postMI survivors than any other conventional ECG-derived repolarization parameters.

?	Normal n=12	PMI-VT n=12	PMI+VT n=12	P value
Age(years)	53짹9	59짹13	63짹13	NS
Sex(Male,%)	4(33)	9(75%)	8(67%)	NS
QTcD(ms)	23.2짹13.0	42.1짹19.4	32.1짹28.9	0.113
PCA ratio2(%)	15.7짹7.2	38.5짹25.7	44.3짹31.5	0.015