[Monophasic action potentials: considerations and limits]

Monophasic action potentials are currents recorded in vivo in the extracellular milieu which can reproduce the repolarisation signal of intracellular action potentials. For a long time unstable and complex to record, they now require simply a firm myocardial contact with a bipolar electrophysiological catheter and modification with recording filters, without a high-pass filter (DC). They have been widely used in recent years to study in vivo modifications of the action potential durations with frequency, epi-, endo-, or intramyocardial cellular topography, endocavity pressure modifications, or antiarrhythmic medication. They allow a unique means of continuous analysis in animals or in patients of the action potentials during polymorphic arrhythmias such as atrial fibrillation, ventricular fibrillation and torsades de pointes, although in these cases the refractory periods can not be measured precisely and continuously, beat after beat. In contrast, their clinical or experimental use in the study of arrhythmias dependent on premature post-depolarisations has without doubt been excessive and disputable, because it appears improbable that authentic premature post-depolarisations could ever be obtained on a monophasic action potential, which always represents the summation of the action potentials of dozens of cells.