Basic Cardiac Electrophysiology: Excitable Membranes

Cardiomyocytes are excitable cells and have the ability to contract after excitation; therefore, each heartbeat is an event of electrical–mechanical coupling. Cardiac electrical activity at different levels can be measured through variable means and modified by different drugs or medical devices. Understanding the basic mechanisms of cardiac excitation is essential not only to a physiologist, but also to a cardiologist, because cardiac arrhythmias are a major health issue in our society and clinical practice. Diagnosis and therapy of arrhythmias require understanding the cause or origin of each arrhythmia and making decisions to control or eliminate the arrhythmia. Advances in basic research enhance our understanding of normal cell, tissue, and organ function (physiology) and also disease processes (pathophysiology), and lead to better clinical diagnosis and improved clinical therapies, either directly or indirectly. Cardiomyocytes are the main cell type of the heart. Their electrical activity is fundamentally a biological process determined by the transmembrane potential, a voltage difference between the intracellular and extracellular compartments. During a normal cardiac cycle, mechanical contraction always follows electrical excitation. This chapter provides a basic overview of membrane excitability of cardiomyocytes and other excitable cells (i.e., neuronal and skeletal).