Basic ECG theory, 12-lead recordings and their interpretation

The recorded electrocardiogram (ECG) remains one of the most vital monitors of a given patient's cardiovascular status and is used today in nearly every clinical setting. This chapter discusses the ECG as a measure of how the heart's electrical activities may change 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, we present the techniques for obtaining ECG data. Electrocardiography has progressed rapidly since it was first employed in the early 1900s. New, smaller, and more sophisticated instruments and innovative analysis techniques are continually being developed. The trend has been toward developing smaller, easier-to-use devices to gather and remotely send information to aid patient diagnosis and treatment.