Epicardial MAPs are extracellularly recorded waveforms that reproduce the depolarization and repolarization time course of transmembrane action potentials with high fidelity. MAP duration is useful in the characterization of the electrophysiological properties that accompany acute myocardial ischemia, as well as various chronic conditions, such as hypertrophy, dilated cardiomyopathy and left ventricular remodeling.
The target site of recording is invariably the lateral LV wall adjacent to the infarct scar. The hand-held probe is placed on the LV base, exerting mild, constant pressure against the epicardium. The probe is gently shifted towards the infarct area, until an abrupt transition to very low amplitude signals is observed; the probe is then slowly withdrawn, until the re-emergence of a MAP signal with a stable baseline, rapid upstroke phase, smooth repolarization phase, and stable duration and amplitude.