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This Article Full Text Full Text (PDF) All Versions of this Article: 289/6/H2602    most recent 00968.2004v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (1) Citing Articles via Google Scholar Google Scholar Articles by Sidorov, V. Y. Articles by Baudenbacher, F. Search for Related Content PubMed PubMed Citation Articles by Sidorov, V. Y. Articles by Baudenbacher, F.

Examination of stimulation mechanism and strength-interval curve in cardiac tissue

¹Department of Biomedical Engineering and ²Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee

Submitted 20 September 2004 ; accepted in final form 13 July 2005

Understanding the basic mechanisms of excitability through the cardiac cycle is critical to both the development of new implantable cardiac stimulators and improvement of the pacing protocol. Although numerous works have examined excitability in different phases of the cardiac cycle, no systematic experimental research has been conducted to elucidate the correlation among the virtual electrode polarization pattern, stimulation mechanism, and excitability under unipolar cathodal and anodal stimulation. We used a high-resolution imaging system to study the spatial and temporal stimulation patterns in 20 Langendorff-perfused rabbit hearts. The potential-sensitive dye di-4-ANEPPS was utilized to record the electrical activity using epifluorescence. We delivered S1-S2 unipolar point stimuli with durations of 2–20 ms. The anodal S-I curves displayed a more complex shape in comparison with the cathodal curves. The descent from refractoriness for anodal stimulation was extremely steep, and a local minimum was clearly observed. The subsequent ascending limb had either a dome-shaped maximum or was flattened, appearing as a plateau. The cathodal S-I curves were smoother, closer to a hyperbolic shape. The transition of the stimulation mechanism from break to make always coincided with the final descending phase of both anodal and cathodal S-I curves. The transition is attributed to the bidomain properties of cardiac tissue. The effective refractory period was longer when negative stimuli were delivered than for positive stimulation. Our spatial and temporal analyses of the stimulation patterns near refractoriness show always an excitation mechanism mediated by damped wave propagation after S2 termination.

cardiac excitability; cathodal stimulation; anodal stimulation; damped wave; optical mapping

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				V. Y. Sidorov, M. C. Woods, and F. Baudenbacher Cathodal stimulation in the recovery phase of a propagating planar wave in the rabbit heart reveals four stimulation mechanisms J. Physiol., August 15, 2007; 583(1): 237 - 250. [Abstract] [Full Text] [PDF]