CELLULAR ELECTROPHYSIOLOGIC BASIS OF CARDIAC-ARRHYTHMIAS

During normal sinus rhythm, the cardiac impulse originates in the sinu s node at a rate appropriate to the age and activity of the animal and spreads in an orderly fashion throughout the atria, the atrioventricu lar (AV) node, the His-Purkinje system, and then throughout the ventri cles. An arrhythmia is an abnormality in the rate, regularity, or site of origin of the cardiac impulse or a disturbance in conduction of th e impulse so that the normal sequence of activation of atria and ventr icles is altered. Cardiac arrhythmias and conduction disturbances occu r in every region of the heart and ore caused by numerous factors. In particular, some are aligned with certain disease states. In the final analysis, however, all arrhythmias and conduction disturbances-regard less of their pathoelectrophysiologic cause-result from critical alter ations, either acute or chronic, in the electrical activity of the car diac myocyte. This review will provide basic information on how normal cardiac electrophysiology can be changed by disease and how these cha nges can lead to conduction disturbances and cardiac arrhythmias.