QRS aberration during atrial fibrillation at rest and during exercise. Effect of a selective potassium channel blocking agent

This study assesses the occurrence of and identifies clinical characteristics associated with the development of aberrant conduction during infusion of the I-kr-blocker almokalant. Class III drugs may induce aberrant conduction by prolongation of cardiac repolarization, especially during atrial fibrillation (AF). Ninety-two patients with AF received a 6-hour almokalant infusion, aiming at conversion to sinus rhythm (SR). Fiftyfive of the patients received an identical infusion during SR. During almokalant infusion, the number of patients with intermittent QRS aberration during AF increased, from 21% to 80% at rest, and was further increased to 89% during exercise, with predominantly left, and sequential bilateral, bundle branch aberrancy. Patients with aberrant conduction showed signs of more advanced myocardial disease. Predictors of the development of QRS aberration were female gender, arrhythmia duration, and decreased left ventricular ejection fraction, while use of calcium antagonists decreased the probability. No patient showed aberration during regular SR. Twenty-one patients experienced aberrantly conducted supraventricular premature beats. in conclusion, aberrant conduction is common during infusion of the I-kr-blocker almokalant during AF, and seems to be more frequent in females and in patients with more advanced myocardial disease.