Abstract
Electrocardiography, one of the most useful tools in the field of cardiology, offers an electrical snapshot of the heart that can potentially reveal information about physiological conditions in the human body. As such, the physician must clearly understand the elements of the electrocardiogram (ECG) from the generation of the normative tracing to the significance of changes in that tracing during various clinical situations. This chapter presents the ECG in its entirety, beginning with the derivation of the leads, axis, and standardization of the recording. The chapter can basically be broken down into four sections: the basics of electrocardiographic generation; description and illustration of the waves and intervals, including the physiology behind each and examples of pathological alterations; myocardial infarction and its differential diagnosis; and other commonly encountered medical scenarios and their respective influence on the ECG. The fourth section of the chapter includes discussion of drug effects of digoxin, metabolic abnormalities, pulmonary diseases, acute pericarditis, pericardial effusion, central nervous system disorders, the preexcitation syndrome, and congenital and acquired heart disease. Updated sections of the chapter in the most recent edition expand upon the early repolarization pattern/J-wave and the prolonged as well as the congenitally shortened QT interval.