Class 1 antiarrhythmic agents have been demonstrated to suppress a variety of clinical arrhythmias; however, their efficacy in the prevention of sudden death has not been established (5). Failure in the management of life-threatening arrhythmias has arisen in part because of the limiting side-effects frequently associated with the use of these agents (22). Episodes of proarrhythmia, sometimes proving fatal, and more tolerable yet limiting side-effects associated with central nervous system penetration, e.g., giddiness, tremor, and convulsions, are quite common with these agents (1 3,18). To try to overcome some of the limitations of presently available antiarrhythmic therapy, we embarked on a programme of research directed toward the development of a novel antiarrhythmic agent with restricted access to the central nervous system.
BW A256C [5(3)-a~no-6-(2,3-dichlorophenyl)-2,3(2,5)-dihydro-3-(5)-imino-2-isopropyl-1,2,4-triazine] is a chemically novel antiarrhythmic agent that reduces in a concentration-dependent fashion the sodium-dependent rate of rise of phase 0 of the cardiac action potential, an action described by Vaughan Williams as class 1 antiarrhythmic action ( 19). In this respect it is more potent than other class 1 agents such as quinidine, lidocaine, disopyramide, and flecainide (2). In common with other class 1 antiarrhythmic agents, the effects of BW A256C are use, frequency, and voltage dependent. However, unlike other agents, BW A256C has no effect on the duration of the action potential and its kinetics of onset of and recovery from use-dependent block are slower than for any previously reported class 1 agent (10). These distinctive properties place BW A256C in subclass 1 C in the present classification of antiarrhythmic agents (6).Pharmacological studies in vivo demonstrate that BW A256C prevents arrhythmogenesis induced chemically by aconitine administration or that induced by coronary