Sudden Cardiac Death. Future progress in the ability to control the problem of sudden cardiac death will require new approaches in applied epidemiology, methods of accurately evaluating therapeutic outcome, and techniques to identify and control those transient risk factors that are responsible for the initiation of fatal arrhythmias. In regard to the latter, transient risk factors are distinguished from classical risk factors in two ways: (1) they are not present continuously over time, thus confounding sampling techniques among a population; and (2) their dynamic nature suggests a proximate role in the initiation of potentially fatal arrhythmias in contrast to the role of classical risk factors in the genesis of the underlying diseases. Transient risk factors derive from the structure/function model of sudden cardiac death, which places structural abnormalities in a conditioning role, establishing the sensitivity to a transient destabilizing influence. In contrast, functional abnormalities are those conditions immediately responsible for destabilizing the system, establishing vulnerability to potentially fatal arrhythmias. They include four categories of risk: (1) transient ischemia and reperfusion; (2) systemic abnormalities, such as hemodynamic dysfunction and fluid and electrolyte imbalance; (3) autonomic fluctuations, both central and cardiac; and (4) cardiac toxic states, including proarrhythmic effects of antiarrhythmic drugs and arrhythmogenic effects of other substances. Sudden cardiac death is a dynamic problem, and its pathogenesis contains dynamic features. The ability to identify transient risk factors and to control them before they exert their influence on a conditioned electrophysiologic system will provide new inroads into the problem of sudden cardiac death.
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