Background: The ECG features of Andersen-Tawil syndrome (ATS) patients with KCNJ2 mutations (ATS1) have not been systematically assessed. This study aimed to define ECG features of KCNJ2 mutation carriers, to determine whether characteristic T-U-wave patterns exist, and to establish whether T-U patterns predict the ATS1 genotype.
Methods and results: In phase I, evaluation of T-U morphology in ECGs of 39 KCNJ2 mutation carriers identified characteristic T-U patterns: prolonged terminal T downslope, wide T-U junction, and biphasic and enlarged U waves. In phase II, ATS1 genotype prediction by T-U pattern was evaluated in the next 147 ECGs (57 other KCNJ2 mutation carriers, 61 unaffected family members, and 29 ATS patients without KCNJ2 mutations), with a sensitivity of 84% and specificity of 97%. Characteristic T-U patterns were present in 91% (87/96), in whom an enlarged U wave was predominant (73%). In phase III, QTc, QUc, and T- and U-wave duration/amplitude were compared in the 96 ATS1, 29 non-KCNJ2 ATS, and 75 normal subjects. In ATS1 patients, QUc, U-wave duration and amplitude, and QTc were all increased (P<0.001), but median QTc and interquartile range (IQR) were just 440 ms (IQR, 28 ms) compared with 420 ms (IQR, 20 ms) in normal subjects and 425 ms (IQR, 48 ms) in ATS non-KCNJ2 patients.
Conclusions: In ATS1 patients, gene-specific T-U-wave patterns resulting from decreased IK1 owing to KCNJ2 mutations can aid diagnosis and direct genotyping. The normal QTc, distinct ECG, and other clinical features distinguish ATS1 from long-QT syndrome, and it is best designated as ATS1 rather than LQT7.