A lead is a device that measures the passage of electrical signals. Leads are used in electrocardiograms to record the electrical activity of the heart (Fig. 1). Leads are also used with pacemakers or Implantable Cardioverter Defibrillator devices (ICDs) to detect abnormal beating of the heart, and to deliver electrical impulses to the heart, in order to correct the abnormal heartbeat, or rhythm (Fig. 2).