Use of Cardiac Electric Near-Field Measurements to Determine Activation Times

Abstract

In a recent paper, we described the behavior of the cardiac electric near-field, E, parallel to the tissue surface during continuous conduction. We found that T_E, the time at which the peak near-field, $\hat E$, occurs, is an accurate marker of local activation time. Examination of experimentally recorded E vector loops revealed a large variety of morphologies. We postulated that propagation around an obstacle could lead to the observed deviations in loop morphology. The purpose of this study was to determine if this was plausible, and if so, whether T_E remains an accurate time marker of local activation under these conditions. We used a monodomain computer model of a sheet of cardiac tissue with a central conduction obstacle immersed in an unbounded volume conductor. Activation times $T_{I_m }$, T_Φ, and T_E were derived from the transmembrane current I_m, the extracellular potential Φ _e, and E, respectively. The obstacle led to deformations of the vector loops, morphologically similar to those observed experimentally, particularly during the initial and terminal phases, and to a lesser degree near the time of $\hat E$. Despite these loop deformations, T_E was an accurate time marker of local activation. We found that T_E was significantly closer to $T_{I_m }$ than T_Φ. We concluded that isochrone maps computed from T_E better reflect intracellular activation patterns than those computed from T_Φ. For a given electrode spacing of 60 μm, the sensitivity to noise of E was significantly less than that of $\dot \phi _e$. Hence, T_E was less affected by noise than T_Φ.© 2003 Biomedical Engineering Society.

PAC2003: 8719Nn, 8719Hh, 8780Tq