other versions

abstract in J. Electrocardiol. 40 Suppl. (2007) page S76-S77

conference proceedings paper in Anatol. J. Cardiol. 7 Suppl 1 (2007) pp 123-124

manuscript for the proceedings paper (better graphics!)

abstract

introduction  Propagation of depolarization and repolarization in myocardium result from an interplay of membrane potential, transmembrane current, and current flow between the cells ("electrotonic coupling"). This process can be represented mathematically with a reaction-diffusion (RD) equation. Even today, solving RD equations for a whole heart still requires a supercomputer. Earlier models relied on predefined action potential (AP) shapes and fixed propagation velocities. It is our purpose to explain the difference between these models for a nonspecialized audience and to show why RD models are important when T waves are studied.

methods  We simulated propagating AP with an RD model of the human heart, which included transmural and LV-RV heterogeneity of membrane properties. Computed activation times served as input to a model that used predefined AP, and to a "hybrid model" that computed AP only in the repolarization phase. Fixed AP were obtained from simulations of isolated cells, and represented the same heterogeneity of cell types as the heart model. The RD model had a spatial resolution of 0.25 mm. The hybrid model was tested with different spatial resolutions. ECGs were computed with all three models.

results  As expected, computed QRS complexes were practically identical in all models. T-waves in the fixed-AP model had 20 to 40% larger amplitudes in the precordial leads V1-V3, became biphasic in lead III, and notched in leads II and aVF. In contrast, the hybrid model produced the same T waves as the RD model at 0.25-mm resolution, but underestimated T-wave amplitude in V1-V3 at lower resolutions.

conclusion  Fixed AP waveforms in a forward ECG model lead to exaggerated T waves. Hybrid models only equal RD models when used with the same spatial resolution. Thus, a model that can be trusted to simulate electrocardiographic T waves correctly still requires a supercomputer.

funding

Computational resources for this work were provided by the Réseau québécois de calcul de haute performance (RQCHP). M. Potse was supported by a postdoctoral research award from the Groupe de recherche en sciences et technologie biomédicale (GRSTB), École Polytechnique and Université de Montréal; and by the Research Center of Sacré-Coeur Hospital, Montréal, Québec, Canada.