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(Circulation Research. 2000;86:e23.)
© 2000 American Heart Association, Inc.

Response to Research Commentary

Effects of Cardiac Microstructure on Propagating Electrical Waveforms

Madison S. Spach, Roger C. Barr

From the Departments of Pediatrics (M.S.S., R.C.B.), Cell Biology (M.S.S.), and Biomedical Engineering (R.C.B.), Duke University Medical Center, Durham, NC.

Correspondence to Madison S. Spach, Box 3475, Duke University Medical Center, Durham, NC 27710. E-mail cspach{at}acpub.duke.edu

Abstract—Electrical waveforms measured during propagation at microscopic level are considerably affected by normal variations in cardiac microstructure as well as by the superfusing fluid. On the basis of evidence we present in this article, we argue that the anisotropic waveform variations discussed here are explained primarily by the associated variations in different microstructural components of myocardial architecture rather than by the effects of the perfusing bath. The results suggest that different components of myocardial architecture have preferential effects on _max and on the shape of the foot of the transmembrane action potential (V_m foot). Resistive discontinuities primarily affect _max, and an additional capacitive component in the local circuit due to the capillaries in interstitial space primarily affects V_m foot. Resistive discontinuities also have an important influence on cardiac conduction. These discontinuities include spatial variations in the size of interstitial space (interstitial resistive discontinuities) and the role of cellular scaling (effects of cell size) when changes occur in the cellular and multicellular distribution of gap junctions during remodeling of normal mature myocardium to proarrhythmic structural substrates. The full text of this article is available at http://www.circresaha.org.

Key Words: discontinuous conduction • anisotropy • action potential foot • capillaries • interstitial discontinuities

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