Development of 3-D Intramural and Surface Potentials in the LV: Microstructural Basis of Preferential Transmural Conduction.
BACKGROUND
Extracellular potentials measured on the heart surfaces are used to infer events that originate deep within the heart wall. We have reconstructed intramural potentials in three dimensions for the first time, and compare these with epicardial and endocardial surface potentials and cardiac microstructure.


RESULTS
Extracellular potentials from intramural point stimulation were measured from a high density 3-D electrode array in the in vivo pig LV. MR and extended volume imaging were used to register electrode locations and characterize fiber and laminar orientations throughout the recording volume. Measured potentials were compared with predictions of tissue-specific bidomain computer activation models. Positive potentials recorded in the LV wall preceded the depolarization wavefront as it spread in the fiber direction. Transverse to this, passive and active potentials spread preferentially in the laminar direction (anisotropy ratio ∼1.6:1). Epicardial surface potentials reflect initial intramural propagation at the stimulus location, but endocardial potentials do not, particularly adjacent to papillary muscles. Measured 3-D potentials were consistently better captured by computer models that incorporate three distinct conductivities aligned with local microstructural axes, but the preferential spread of potentials in the laminar direction was not fully predicted.


CONCLUSIONS
This study provides evidence for preferential transmural conduction and raises questions about the extent to which intramural electrical events can be inferred from endocardial potentials.
Auckland Bioengineering Institute, The University of Auckland, New Zealand.
Bryan J
BJ
Caldwell
Auckland Bioengineering Institute, The University of Auckland, New Zealand.
Mark L
ML
Trew
Auckland Bioengineering Institute, The University of Auckland, New Zealand.|Department of Physiology, The University of Auckland, New Zealand.
Ian J
IJ
Legrice
Auckland Bioengineering Institute, The University of Auckland, New Zealand.|Department of Physiology, The University of Auckland, New Zealand.
Bruce H
BH
Smaill
D000200:Action Potentials; D000818:Animals; D002304:Cardiac Pacing, Artificial; D003198:Computer Simulation; D056149:Epicardial Mapping; D006329:Heart Conduction System / Q000033:anatomy & histology / Q000502:physiology*; D006339:Heart Rate; D006352:Heart Ventricles / Q000033:anatomy & histology; D023421:Models, Animal; D008955:Models, Cardiovascular; D034421:Sus scrofa; D013997:Time Factors; D016277:Ventricular Function, Left
anisotropy; computer modeling; electrical mapping; extracellular potential; ventricular microstructure