29. The electrocardiogram
29. The electrocardiogram
- Gillian Pocock, Gillian PocockSenior Lecturer in Clinical Science, Canterbury Christ Church University, Canterbury, UK
- Christopher D. RichardsChristopher D. RichardsEmeritus Professor of Experimental Physiology, Division of Physiology, Pharmacology and Neuroscience, Faculty of Life Sciences, University College London, London, UK
- and David A. RichardsDavid A. RichardsAssociate Professor, Department of Basic Pharmaceutical Sciences, Husson University School of Pharmacy, Bangor, Maine, USA
Abstract
This chapter discusses the initiation of the heartbeat which begins with the pacemaker activity of the sinoatrial (SA) node. It demonstrates how a heartbeat spreads across the heart from the right atrium to the left before passing to the ventricles by way of the atrioventricular (AV) node and the bundle of its left and right branches. Since the cardiac myocytes form a syncytium, an electrical disturbance in one region can spread across the whole heart in much the same way as the conduction of the action potential in unmyelinated nerve fibres. The chapter examines how the heart remain depolarized as the wave of excitation proceeds, while other regions are polarized and at rest. Local electrical circuits are established between these regions which permit the flow of small currents through the extracellular fluid.
