Wolff-Parkinson-White (WPW) Syndrome

Electrical signals from the atrium normally go through the atrioventricular (AV) node to reach the ventricles.  The normal conduction down the AV node prevents extra beats from occurring and keeps the next beat from happening too soon. People with WPW Syndrome have an extra, or accessory, pathway that may cause a re-entry circuit, resulting in a very rapid heart rate called supraventricular tachycardia (SVT). 

Patient with atrial fibrillation may also have rapid ventricular rate when rapid and chaotic electric impulses from the atrial are transmitted directly through the accessory pathway to the ventricles. This may result in ventricular fibrillation.