Cardiac action potential mapping is an important tool for both clinicians and researchers. Analysis of the monophasic action potential (MAP) can lead to insight regarding ionic flux across membranes, electro-mechanical coupling, activation time, repolarization and depolarization cycles, and arrhythmia. More importantly, MAP recordings provide insight into local cellular electrophysiology, which can provide a very precise index of ischemia compared to measurements from surface (skin) electrodes.
MAP recordings have been conducted for over a century, with the earliest experiments in 1882 by Burdon-Sanderson and Page [1,2]. A number of mid 20th century action potential compilations were also made by Hodgkin (1951) and Grundfest (1947, 1961) using wick, pressure, and intracellular electrodes that facilitated an understanding of membrane structure and properties [3,4]. These studies were also important for elucidating the sequence of chemical and electrical events that occur during impulse propagation. Other clinical uses of MAP recording today include:
In our lab, action potential waveforms are acquired directly from the myocardium. Several methods exist for the acquisition of such signals. The major methods include the use of glass micropipette electrodes, metal electrodes of various design, multielectrode arrays, optical mapping, and contact or non-contact endocardial mapping. There are various designs for metal recording electrodes which are employed to monitor action potential waveforms extracellularly.
Our method involves using a needle electrode with two embedded conductors. The spacing between the active and reference conductors can be manipulated to control the sensing area. A permutation to this method involves using an internal conductor needle and the cannula of the needle as the reference electrode. The internal conducting wire is electrically isolated from the cannula. In a monopolar configuration, the needle is a single shaft, and the reference is taken from the subject ground. Our most frequently used electrode spacing is 0.30 mm, which allows for very local recording of myocardial activity.
Future projects in our lab include detailed cardiac ischemia studies using a local infarct model and the identification of ischemic regions and border zones. We are also in the process of setting up an optical mapping system that will allow monitoring the wavefront of propagation around regions of interest.
Needle electrodes: Top left: Concentric needle
at 175x. Top right: Monopolar needle tip at 175x.
Bottom left: Single fiber needle at 80x. Bottom right: Side port of single fiber needle at 175x.
Photos taken with Keyence VXH-100 digital microscope microscope by Maneesh Shrivastav.
© Visible Heart Lab/Medtronic.
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