Atrioventricular 1:1 tachycardia effectively terminated by antitachycardia pacing : What is your diagnosis?

This case describes a tachycardia with a 1:1 atrioventricular relationship that was effectively terminated with antitachycardia pacing by the implantable cardioverter defibrillator. The differential diagnosis and clues that allow the reader to establish the correct diagnosis are discussed. The case also serves to analyse technical features of Boston Scientific dual-chamber defibrillators.