Current status of monophasic action potential recording: theories, measurements and interpretations

Time for primary review 26 days. Monophasic action potentials (MAPs) are extracellularly recorded wave forms that, under optimal conditions, can reproduce the repolarization time course of transmembrane action potentials (TAPs) with high fidelity 1–3. While TAP recordings require the impalement of an individual cardiac cell by a glass-microelectrode and therefore generally are limited to in vitro preparations, MAPs can be recorded from the endocardium and epicardium of the in situ beating heart, including that of human subjects. MAP recordings therefore are suitable for studying the characteristics of local myocardial electrophysiology, especially of repolarization, in the clinical setting. This has made MAP recordings an important bridge between basic and clinical electrophysiology in multiple areas of arrhythmia research 4. Despite the growing use of the MAP recording method, there still is surprisingly little hard data on the exact mechanism by which MAPs are created and recorded. New methods for recording MAPs recently have been proposed, and new theories and models have been suggested to explain the mechanisms that underlie the genesis of the MAP signal. There have been attempts to record MAPs from sites within the myocardial wall, an effort spurred on by the discovery that mid-myocardial cells (M-cells) have different repolarization characteristics than either epicardial or endocardial cells 5, and these different characteristics have been found to be important for the development of torsade de pointes arrhythmias 6. This article attempts to review the available information on the MAP genesis and its particular recording modes. It also highlights some important MAP quality criteria and guidelines for correct interpretation of MAPs and how to avoid artifacts. Last but not least, important differences between unipolar and bipolar recordings of both MAPs and conventional electrograms will be discussed, as they pertain to the fidelity and spatial resolution of these recordings. … * Tel.: +202-745-8398; fax: +202-745-8473; e-mail: mfranz@washington.va.gov