Depolarization-repolarization inhomogeneity after repair of tetralogy of Fallot. The substrate for malignant ventricular tachycardia?

BACKGROUND

We have previously shown that QRS prolongation (> or = 180 ms) is a risk marker for sustained ventricular tachycardia (VT) late after repair of tetralogy of Fallot (rTOF). We have now examined the dispersion of QT and its components QRS and JT, in an attempt to determine whether any association exists between these measurements and the presence of VT in these patients.

METHODS AND

RESULTS

QRS duration and QT/QRS/JT dispersion were measured manually from standard ECGs in 10 syncopal rTOF patients (21.4 +/- 4.6 years after repair; group 1) with QRS > or = 180 ms and with documented VT and were compared with 9 rTOF patients with QRS > or = 180 ms and no VT (group 2), 40 rTOF patients with QRS < 180 ms and no clinical arrhythmias (group 3), and 40 nontetralogy control subjects (20 with right bundle-branch block [group 4] and 20 with normal ECG patterns [group 5]). Mean QT dispersion (62 +/- 36 ms) in the tetralogy patients was greater than in the nontetralogy control subjects (34 +/- 10 ms, P < .001). There were significant differences in all measured parameters between groups 1 and 3 and more importantly between groups 1 and 2. QRS dispersion in group 1 also correlated with QRS duration but not with JT dispersion.

CONCLUSIONS

Our data suggest that both depolarization and repolarization abnormalities are associated with VT after rTOF. Furthermore, increased QT, QRS, and JT dispersions, combined with a QRS > or = 180 ms, refine risk stratification for VT in these patients.