Monophasic action potential recordings: evaluation of antiarrhythmic drugs

The use of MAP recording techniques has been said to have bridged the gap between basic in vitro investigation of the transmembrane action potential and observations made in situ from the beating heart. With regard to antiarrhythmic agents, MAP recordings are particularly useful in evaluating drugs which prolong repolarization. The simultaneous measurement of MAP and ERP at the same site permits the comparison of drug effects on repolarization and refractoriness. The ability to safely and reliably record the MAP contributes importantly to the evaluation and classification of antiarrhythmic drug effects in vivo and may ultimately lead to more rational selection of drug therapy for individual patients. Antiarrhythmic drug effects demonstrated with MAP recordings have generally shown good agreement with the Vaughan Williams classification of electrophysiological actions. An important key to drug efficacy may be that some drugs prolong refractoriness beyond their effect on repolarization. Conversely, a potential explanation for proarrhythmia may lie in slowing of conduction without the concomitant protective effect of postrepolarization refractoriness. The phenomenon of use dependence, which has been demonstrated for many drugs, suggests why an agent that prevents induction of arrhythmia during programmed stimulation in the electrophysiology laboratory may not prevent spontaneous arrhythmia initiation at slower heart rates. The paramount task of clinical electrophysiology is the successful treatment of rhythm disturbances. The more detailed and quantitative evaluation of drug effects afforded by MAP recordings may ultimately result in the more effective use of antiarrhythmic drugs in general and to more precise tailoring of therapy for individual patients.