The JT interval as a depolarization independent measurement of repolarization: Lessons from catheter ablation of the Wolff-Parkinson-White syndrome

In patients with Wolff-Parkinson-White syndrome (WPW), preexcitation precludes accurate assessment of the ventricular repolarization by the QT(c). In patients with long QT syndrome, it has been demonstrated that the JT(c) does not change when depolarization abnormalities develop. We hypothesized that this phenomenon should also be applicable to WPW patients. To test this, we assessed the surface ECG of 29 patients (16 males, 13 females) with WPW pre- and postablation. The QRS, QT, and JT intervals were measured pre- and postablation at 50 mm/s paper speed in leads II and V-2. QT(c) and JT(c) were calculated according to Bazett's formula. The average age was 12.8 +/- 4.9 years (range 1.5-21). All patients had no residual preexcitation on postablation EGG. Early and late follow-up ECGs were obtained at 32 +/- 34 days and 388 +/- 197 days postablation, respectively. Both the QRS and the QT(c) intervals shortened significantly on the postablation versus preablation ECGs (QRS: 115 +/- 23 ms vs 89 +/- 15 ms, respectively; P < 0.0001), (QT(c): 454 +/- 26 vs 423 +/- 23, respectively; P < 0.001). The preablation JT(c) interval did not change, postablation (319 +/- 21 vs 323 +/- 23, respectively; P > 0.2). Also, the JT(c) interval did not change between early and late follow-up, postablation. JT(c) is an independent measure of repolarization, not related to depolarization. JT(c) may be a useful tool in assessing repolarization in patients with WPW and other depolarization abnormalities.