Physiology of the Cardiac Conduction System

The diagnosis and management of cardiac arrhythmias has progressed rapidly as a science. Advances in the ability to diagnose and either suppress or eliminate arrhythmic substrates has taken an exponential trajectory. Whether utilizing three-dimensional electroanatomic mapping systems for examining complex arrhythmias in patients with palliated congenital heart disease or genetic analysis in a search for evidence of heritable arrhythmia syndromes, technological advances have improved our ability to observe, diagnosis, and manage rhythm disturbances in patients from fetal life through adulthood. To fully harness the possibilities offered by these new technologies, a detailed understanding of cardiac anatomy and cellular electrophysiology is imperative. The orderly spread of electrical activity through the myocardium is a wellchoreographed process involving the coordinated actions of multiple intracellular and membrane proteins. Abnormalities in the physical structure of the heart or the function of these cellular proteins may serve as the substrate for arrhythmias. Cardiac myocytes like other excitable cells maintain an electrical gradient across the cellmembrane.Various proteins including ion channels, ion pumps, and ion exchangers span the membrane contributing to the voltage difference between the inside and outside of the cell. Because these integral membrane proteins, along with membrane receptors and regulatory proteins, form the basis of the electrophysiologic properties of the heart, a knowledge of their structure and function is necessary to understand fully cardiac arrhythmias, as well as for the appropriate selection of antiarrhythmic pharmacological agents.