SEQUENTIAL BILATERAL BUNDLE-BRANCH BLOCK DURING DOFETILIDE, A NEW CLASS-III ANTIARRHYTHMIC AGENT, IN A PATIENT WITH ATRIAL-FIBRILLATION

Introduction: The mechanism of wide QRS complex tachycardias during do fetilide infusion was studied in a patient with atrial fibrillation. M ethods and Results: Endocardial recordings from the intraventricular c onduction system showed that dofetilide caused ''classic'' aberrant co nduction (Ashman phenomenon, typical QRS morphology) at high prematuri ty ratios (preceding interval = 1.78 X coupling interval -290), thus m imicking ventricular ectopy. In addition, there was frequent sequentia l bilateral bundle branch block, caused by a significant difference in preceding bundle-to-bundle intervals (mean difference +/- 1 SD: 74 +/ - 26 msec). Conclusion: The present findings may prove helpful in the clinical assessment of wide QRS complex rhythms after dofetilide and p ossibly other ''Pure'' Class III antiarrhythmics.