Abstract
Direct-current cardioversion is an important means of managing arrhythmias. During treatment, carefully synchronizing energy delivery to the QRS complex is necessary to avoid ventricular fibrillation caused by a shock during the vulnerable period of ventricular repolarization, that is, a shock on the T wave. The presence of an accessory pathway and ventricular preexcitation can lead to difficulty in distinguishing the QRS complex from the T wave because of bizarre, wide, irregular QRS complexes and prominent repolarization. We present the cases of 2 patients who had iatrogenic ventricular fibrillation from inappropriate T-wave synchronization during direct-current cardioversion of preexcited atrial fibrillation. Our experience shows that rapidly recognizing the iatrogenic cause of VF and immediate treatment with unsynchronized defibrillation can prevent adverse clinical outcomes.