[In vivo registration of monophasic action potentials--new possible applications in clinical electrophysiology].

Monophasic action potential (MAP) recordings have gained a more important role during the recent years. A new application for their use in the clinical laboratory is the precise differentiation between ventricular tachycardias and ventricular fibrillation. A correct diagnosis of the arrhythmic episode may be of relevance for the determination of the defibrillation threshold during implantation and testing of implantable cardioverter defibrillators. Diagnostic studies and ablation procedures of triggered arrhythmias represent another indication for MAP recordings. The focus of enhanced automaticity can be located by the detection of afterdepolarizations which allows a reliable ablation using a MAP-ablation combination catheter. Recently, a new phenomenon has been reported regarding the relationship between ventricular repolarization and excitability during programmed electrical stimulation in humans. Each additional extrastimulus was able to capture the myocardium at a less complete repolarization level than the previous one. This "facilitation of excitability" phenomenon or "encroachment" was correlated with the initiation of ventricular tachyarrhythmias. The involved mechanism can be modulated pharmacologically and might therefore play a role in the antiarrhythmic treatment of patients with ventricular arrhythmias.