CONTACT PROBES FOR MAP RECORDING: A COMPUTATIONAL STUDY

Abstract

In this computational study, we investigate the effects of a contact probe's design on the monophasic action potential (MAP) it records. Particularly, we focus on tip size and electrode geometry. A MAP is recorded when the tip of the contact probe is pressed against myocardial tissue and an action potential propagates through the tissue. Our 2-dimensional tissue model incorporates Luo–Rudy I membrane kinetics to simulate the transmembrane action potential (TAP), and the tissue injury induced by the contact probe is modeled after ischemic conditions. We compare our simulated MAPs to the TAPs in the model. Our results show that the correlation between MAP and TAP signals is affected by both the shape of the contact probe's active electrode and the size of the probe's tip. We found that an asymmetrical active electrode which records MAPs from the downstream region of injury (e.g., right side of injury for a wave propagating across the tissue from left to right) very accurately reflects the TAP of the healthy tissue. Further, our findings suggest that the optimal size for a contact probe's tip is between 0.64 and 1 mm 2. If the tip is very small (0.04 mm 2), the resulting region of injury is too small to maintain a stable transmembrane potential, and the recorded MAPs are distorted. On the other hand, very large probe tips (>1 mm 2) covered with standard active electrodes focus their measurements too much on the interior of the injury and thus do not accurately describe the behavior of the injury currents. The results of our study could have implications on the design of contact probes used for recording MAPs in vivo.