Electrophysiology Laboratory Survival Guide Part 1: Electrogram Basics, Catheters, and Basic Intervals.

The term 'cardiac electrogram' (EGM) was initially used to describe the surface ECG, but now EGMs represent the electrical potential within the immediate vicinity of a catheter (including pacemaker and implantable cardioverter defibrillator lead) within the heart. These EGMs are generated from electrodes on catheters that are placed in different regions of the heart: the right atrium, the right ventricle, in the coronary sinus, and near the His bundle. These EGMs, in conjunction with a surface ECG, can then be used to study the timing of electrical activity within the heart, as well as arrhythmias in the cardiac electrophysiology (EP) lab. The goals of this article are to give readers the basics of EGMs, the basics of cardiac EP catheters, and the placement of EP catheters in the heart, and to introduce readers to EGMs and intervals measured.