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A three dimensional electroanatomic mapping system (CARTO, Biosense Webster) can visualise the activation sequence during normal or abnormal rhythm, and has recently been used as a guide for catheter ablation for some tachyarrhythmias. Activation time at each site is measured from a bipolar (or a unipolar) electrogram and is determined as the interval between the QRS onset and the time minimum of the first derivative (Vmin) of the QRS deflection. On the other hand, the time maximum of the first derivative (Vmax) of the T wave, which is measured from a unipolar electrogram, is shown to be coincident with repolarisation at each site.
We report on a 16 year old Japanese male with congenital long QT syndrome who had episodes of syncope and a prolonged corrected QT interval (589 ms) with a notched configuration (below left). During the electrophysiological study, after obtaining informed consent, endocardial mapping of unipolar recording in the right and left ventricle was performed during constant atrial pacing (80 beats/min). We constructed maps of both activation time (panels A (right anterior oblique (RAO) 30°) and B (left anterior oblique (LAO) 45°)) and repolarisation time, which was defined as the interval between the QRS onset and the Vmax of the T wave (panels C (RAO 30°) and D (LAOf 45°)). Each colour bar of the maps is relative to the QRS onset of surface ECG lead V1, ranging from 4 ms (orange) to 84 ms (purple) in the activation time map, and from 263 ms (orange) to 494 ms (purple) in the repolarisation time map, respectively. Endocardial activation started at the inferoseptum and the anteroseptum of the left ventricle (LV) simultaneously and spread to the right ventricle (RV) and the rest of the LV. The free wall of the right ventricular outflow tract was activated last. In contrast, the repolarisation sequence was considerably opposite to the activation sequence. The left and right ventricular outflow tract repolarised first and the apex of the RV and the LV repolarised last. The dispersion of the repolarisation time was increased (231 ms) in this case compared with the averaged dispersion of the repolarisation time in three normal controls (172 (10) ms), which may be arrhythmogenic in this syndrome.