Clinical value of monophasic action potentials

The method of monophasic action potential (MAP) recording has experienced a significant surge in interest since the introduction of the contact electrode, which in contrast to the suction electrode, allows the safe and simple use of this technique in the clinical electrophysiology laboratory. MAP recording not only provide for a more precise determination of local activation, but most importantly, permit direct measurement of myocardial repolarization and action potential duration (APD), respectively. This had led to new insights into the cycle-length-dependence of the human APD, both in response to single extrastimuli and to steady-state heart rate changes. An advancement of the contact electrode catheter design now permits simultaneous pacing and MAP recording, and thereby, simultaneous determinations of APD and effective refractory periods (EPP) at the same endocardial site in the human heart. MAP recordings have demonstrated significant usefulness in the direct monitoring of antiarrhythmic drug effects, both in terms of dosage control and in the direct measurement of antiarrhythmic drug effects on the relationship between ERP and APD (ERP/ARD-ratio). Because MAP recordings reflect the local cellular electrophysiology, they also provide a more sensitive and precise index of myocardial ischemia than conventional ECG recordings. This can be utilized to assess the success of revascularizing procedures directly during or after the intervention. Recently, MAP recordings helped to discover early after-depolarizations in patients with "torsade de pointes", providing a possible explanation for the mechanism of polymorphous ventricular tachycardia in man.