Cardiac arrhythmias: Introduction, electrophysiology of the heart, action potential and membrane currents

Abstract

Myocytes represent the functional unit of cardiac muscle; nonetheless, the heart behaves more or less like an electrical syncytium, whose global activity depends on low resistance coupling between the myocytes. The term “more or less” is used here intentionally to imply that while the activity intrinsic to individual myocytes is affected by coupling, its features remain recognizable within the context of the whole heart and are important to determine its function. Electrical changes within the myocytes play an important role to initiate the cardiac contraction. This chapter addresses: (a) the electrical activity of individual myocytes, namely, the resting membrane potentials and action potentials; (b) the way action potentials are conducted throughout the heart to initiate coordinated contraction of the entire heart; and (c) the transmembrane ionic currents underlying cardiac action potential.