Basic ECG theory, 12-lead recordings, and their interpretation

The recorded electrocardiogram (ECG) remains as one of the most vital monitors of a patient's cardiovascular status and is used today in nearly every clinical setting. This chapter discusses the ECG as a measure of how the electrical activity of the heart changes over time, as action potentials within each myocyte propagate throughout the heart during each cardiac cycle. By utilizing the resultant electrical fields present in the body, electrodes can be placed around the heart to measure potential differences as the heart depolarizes and repolarizes. Furthermore, various techniques for obtaining ECG data are presented. Electrocardiography has progressed rapidly since it was first employed back in the early 1900s. New instruments that are smaller and more sophisticated, as well as innovative analysis techniques, are continually being developed. The trend has been toward developing smaller, easier-to-use devices that can gather and remotely send a wealth of information to aid patient diagnosis and treatment.