Is this pacemaker working properly? Prolongation of the atrial escape interval following activation of the ventricular safety pacing algorithm in a dual-chamber implantable cardioverter defibrillator with atrial-based, lower rate timing.

With the introduction of various new pacing features and algorithms, 12-lead electrocardiogram analysis of paced rhythms can be a challenging undertaking. An incorrect interpretation may lead to an inappropriate medical decision in the care of such patients. The authors present an interesting paced 12-lead electrocardiogram that posed a diagnostic challenge.