title: Evaluation of the spatial aspects of T-wave complexity in the long-QT syndrome.
abstract: BACKGROUND
  The duration of the QT interval is only a gross estimate of repolarization. Besides its limited accuracy and reproducibility, it does not provide information on the morphology of the T wave; thus, morphologic alterations such as notches can be only qualitatively described but not objectively quantified.
  
  
  RESULTS
  To measure the complexity of repolarization in the long-QT syndrome (LQTS) patients, we previously applied principal component analysis to body surface mapping and found it useful in distinguishing normal from abnormal repolarization patterns (sensitivity, 87%). In the present study, we applied principal component analysis to 12-lead Holter recordings. The index of complexity of repolarization that we have developed (CR24h) reflects the average 24-hour complexity of repolarization and is mathematically defined as the average ratio between the second and the first eigenvalue. We studied 36 LQTS patients and 40 control subjects. A mean of 22+/-1.3 ECG recordings at 1-hour intervals was used in each patient, and a total of 1655 recordings were analyzed. CR24h was significantly higher in LQTS than in control subjects (34+/-12% versus 13+/-3%; P<.0001). A CR24h exceeding 2 SD above the mean of the control group (>20%) was present in 32 of 36 patients (88%). The negative predictive value of CR24h in LQTS was 88%, and the combination of prolonged QT and abnormal CR24h identified all LQTS patients from normal subjects, including 4 affected symptomatic individuals with a normal QT interval duration, suggesting that CR24h provides information independent of QT duration.
  
  
  CONCLUSIONS
  Our data suggest that principal component analysis applied to 24-hour, 12-lead Holter recording adequately quantifies the complexity of ventricular repolarization and may become a useful noninvasive diagnostic tool in LQTS.
authors.affiliation: Molecular Cardiology and Electrophysiology, Fondazione Salvatore Maugeri, Pavia, Italy.
authors.forename: S G
authors.initials: SG
authors.lastname: Priori
authors.forename: D W
authors.initials: DW
authors.lastname: Mortara
authors.forename: C
authors.initials: C
authors.lastname: Napolitano
authors.forename: L
authors.initials: L
authors.lastname: Diehl
authors.forename: V
authors.initials: V
authors.lastname: Paganini
authors.forename: F
authors.initials: F
authors.lastname: Cantù
authors.forename: G
authors.initials: G
authors.lastname: Cantù
authors.forename: P J
authors.initials: PJ
authors.lastname: Schwartz
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D004562:Electrocardiography; D005260:Female; D006801:Humans; D008133:Long QT Syndrome / Q000503:physiopathology*; D008297:Male