Basic Physiology of Ion Channel Function

It is a common habit that the first chapter of a book on electrical diseases deals with the basic principle of cardiac cellular electrophysiology. It is also common behavior that readers (almost a rule if they are clinicians) skip this chapter to directly enter what they consider the heart of the matter: clinical rhythmology. However, skipping the first chapter would be a great mistake. In cardiac electrophysiology, there is a continuum of concept between the function of ion channel molecules and the clinical phenotype (Figure 1-1). As an example, it would be almost impossible to understand heritable or iatrogenic cardiac channelopa- thies without knowing what an action potential is and how it is formed. The beauty of cardiac electrophysiology is that it is the same elementary electrical signal arising from billion of single channel proteins that is summed up at the level of a single cell to generate action potentials and is also summed up in time and space to generate a surface electrocardiogram (EKG) signal. Thus cardiac electrophysiology offers the unique opportunity to obtain different levels of view of the same phenomenon either nanoscopically (at the level of a channel pore) or macroscopically (at the level of the whole organ). The present chapter aims to provide the clinical cardiologist specialized in arrhythmias with the very minimum that should be known about ion channel function to understand serenely the mechanisms generating these either acquired or inherited arrhythmias and the fundamentals of antiarrhythmic drug therapy.