T wave components in LQTS 1

• CIRCEP.110.958827Published online before print April 21, 2011
• Original Article

Detection of Extra-Components of T Wave by Independent Component Analysis in Congenital Long QT Syndrome

1. Hitoshi Horigome,
2. Yasuhiro Ishikawa,
3. Junko Shiono,
4. Mari Iwamoto,
5. Naokata Sumitomo and
6. Masao Yoshinaga

1. ¹ University of Tsukuba, Tsukuba, Ibaraki, Japan;
2. ² Ishikawa Clinic & Toyohashi University of Technology, Toyohashi, Aichi, Japan;
3. ³ Ibaraki Children's Hospital, Mito, Ibaraki, Japan;
4. ⁴ Yokohama City University, Yokohama, Japan;
5. ⁵ Nihon University, School of Medicine, Tokyo, Japan;
6. ⁶ National Hospital Organization Kagoshima Medical Center, Kagoshima, Jap
   hhorigom@md.tsukuba.ac.jp

Abstract

Background—The main EKG criteria for the diagnosis of long QT syndrome (LQTS) include abnormal T wave morphology as well as prolonged QT interval. The T wave in LQTS probably includes additional components of myocardial repolarization process, which is derived from aberrant ion currents. We investigated whether independent component analysis (ICA) can extract such abnormal repolarization component.

Methods and Results—Digital EKG data were obtained as time series from 10 channels using 20 surface electrodes in 22 patients with genetically-confirmed LQTS type 1 (LQT1) and 30 normal subjects. In each case, T wave area was analyzed by radical ICA after noise reduction by the wavelet thresholding method. Furthermore, inverse ICA was applied to determine the origin of each independent component (IC). Radical ICA revealed that a T-wave consisted of four basic ICs in all control subjects, whereas five or more (mostly 6) ICs were identified in all 22 cases of LQT1. The extra ICs, which were not evident in normal subjects, were assumed to contribute to the formation of abnormal T-wave morphology. The extra ICs were identified even in those patients with normal QTc values and those taking β-blockers. Inverse ICA indicated that the additional ICs originate predominantly from the late phase of the T wave of the left ventricle.

Conclusions—Extra ICs appear during repolarization in all LQT1 patients but not in normal subjects. ICA is a potentially useful multivariate statistical method to differentiate LQT1 patients from normal subjects.