EVALUATION OF THE SPATIAL-ASPECTS OF T-WAVE COMPLEXITY IN THE LONG-QTSYNDROME

Background The duration of the QT interval is only a gross estimate of repolarization. Besides its limited accuracy and reproducibility, it does nor provide information on the morphology of the T wave, thus, mo rphologic alterations such as notches can be only qualitatively descri bed but not objectively quantified. Methods and Results To measure the complexity of repolarization in the long-QT syndrome (LQTS) patients, we previously applied principal component analysis to body surface ma pping and found it useful in distinguishing normal from abnormal repol arization patterns (sensitivity, 87%). In the present study, we applie d principal component analysis to 12-lead Holter recordings. The index of complexity of repolarization that we have developed (CR24h) reflec ts the average 24-hour complexity of repolarization and is mathematica lly defined as the average ratio between the second and the first eige nvalue. 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 val ue of CR24h in LQTS was 88%, and the combination of prolonged QT and a bnormal CR24h identified all LQTS patients from normal subjects, inclu ding 4 affected symptomatic individuals with a normal QT interval dura tion, suggesting that CR24h provides information independent of QT dur ation. 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 nonin vasive diagnostic tool in LQTS.