Sequential Bilateral Bundle Branch Block During Dofetilide, A New Class III Antiarrhythmic Agent, In a Patient with Atrial Fibrillation

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Abstract
The mechanism of wide QRS complex tachycardias during dofetilide infusion was studied in a patient with atrial fibrillation. Endocardial recordings from the intraventricular conduction system showed that dofetilide caused "classic" aberrant conduction (Ashman phenomenon, typical QRS morphology) at high prematurity ratios (preceding interval = 1.78 x coupling interval--290), thus mimicking ventricular ectopy. In addition, there was frequent sequential bilateral bundle branch block, caused by a significant difference in preceding bundle-to-bundle intervals (mean difference +/- 1 SD: 74 +/- 26 msec). The present findings may prove helpful in the clinical assessment of wide QRS complex rhythms after dofetilide and possibly other "pure" Class III antiarrhythmics.