Spread of excitation in 3-D models of the anisotropic cardiac tissue. III. Eects of ventricular geometry and ®ber structure on the potential distribution Piero Colli Franzone a,* , Luciano Guerri b , Micol Pennacchio c , Bruno Taccardi d a Dipartimento di Matematica, Universit  a di Pavia, and Istituto di Analisi Numerica del CNR, Via Abbiategrasso 209, 27100 Pavia, Italy b Dipartimento di Matematica, Universit  a di Alessandria, Italy c Istituto di Analisi Numerica del CNR, Pavia, Italy d Nora Eccles Harrison Cardiovascular Research and Training Institute, University of Utah, Salt Lake City, UT, USA Received 1 August 1997; received in revised form 6 February 1998 Abstract In a previous paper we studied the spread of excitation in a simpli®ed model of the left ventricle, aected by ®ber structure and obliqueness, curvature of the wall and Pur- kinje network. In the present paper we investigate the extracellular potential distribution u in the same ventricular model. Given the transmembrane potential v, associated with the spreading excitation, the extracellular potential u is obtained as the solution of a lin- ear elliptic equation with the source term related to v. The potential distributions were computed for point stimulations at dierent intramural depths. The results of the sim- ulations enabled us to identify a number of common features which appear in all the potential patterns irrespective of pacing site. In addition, by splitting the sources into an axial and conormal component, we were able to evaluate the contribution of the clas- sical uniform dipole layer to the total potential ®eld and the role of the superimposed axial component. Ó 1998 Elsevier Science Inc. All rights reserved. * Corresponding author. Tel.: +39-382 529 600; fax: +39-382 529 566; e-mail: colli@drag- on.ian.pv.cnr.it. 0025-5564/98/$19.00 Ó 1998 Elsevier Science Inc. All rights reserved. PII: S 0 0 2 5 - 5 5 6 4 ( 9 8 ) 1 0 0 0 4 - 4 Mathematical Biosciences 151 (1998) 51±98