Atrioventricular Junctional Parasystole with Ventricular Fusion Beats Due to Complicating Wolff-Parkinson-White Syndrome

We present a case of atrioventricular (AV) junctional parasystole manifesting with ventricular fusion beats due to the presence of an accessory AV conduction pathway. Ventricular fusion beats are usually impossible in AV junctional parasystole. In the reported case the ventricular fusion occurs because the ectopic AV junctional impulse is conducted through the His bundle, whereas the sinus impulse is conducted to the ventricles through the Kent bundle. (Chest 1989; 96:414–15)