Analysis of the Shape of the T-wave in Congenital Long-QT Syndrome Type 3 by Geometric Morphometrics

The characteristic shape of the T-wave in congenital long -QT syndrome type 3 (LQTS3) is considered a late-onset T-wave. We analyzed the difference in the shapes of T-waves between LQTS3 cases and normal subjects using generalized Procrustes analysis (GPA). The J and Q points of V5 in the ECGs of LQTS3 cases are shifted to the upper left compared to those of normal subjects. SdFmax is the point on the ECG where the second derivative is first maximized. The curvature of the T-wave takes the first maximum value at SdFmax where the T-wave has the smallest radius of curvature.The SdFmax in LQTS3 cases is shifted to the lower right compared to normal subjects. The interval from J to SdFmax of LQTS3 cases is expanded compared with that of normal subjects. As a result of principal component analysis (PCA) of the Procrustes mean shape of the T-wave landmarks, the second principal component (PC2) shows the shift in SdFmax to the lower right. These results can quantitatively explain why the T-wave of LQTS3 cases looks like a late-onset T-wave. Fitted to a multivariate logistic regression model, LQTS3 cases and normal subjects can be distinguished by the second independent component (IC2).