Detrimental effects of electrical fields on cardiac muscle

The use of controlled electrical shock as a therapy to manage cardiac arrhythmia is a practice commonly used today. High intensity electrical fields are generated near the shock electrodes, and if the electrodes are placed directly on or inside the heart as is often the case, tissue injury and dysfunction may result if the shock intensity is too high. Many factors influence the degree of dysfunction, including the intensity of the shock pulse, duration of the pulse, waveform shape, size and position of the electrodes, and physiological state of the heart. One of the most immediate indications of aberrant cardiac function is an abnormality in the electrocardiogram, which results from field-induced changes in cellular electrophysiology. This article reviews results obtained primarily from animal experiments which delineate the intensities of electrical field that produce electrical dysfunction at various structural levels of the heart. Possible mechanisms underlying the detrimental effects of electrical fields are presented, with the main focus on electroporation of the cell membrane. Other mechanisms that are described include formation of oxygen-derived free radicals, conformational damage to ionic pumps/channels, barotrauma, and hyperthermia. Differences between cathodal and anodal shock effects, as well as factors which may ameliorate electrical field-induced cardiac dysfunction, are also discussed.