ROLE OF CONDUCTION IN THE GENESIS OF ALTERNANS OF ACTION POTENTIAL DURATION IN A SIMULATED ONE DIMENSIONAL FIBER

• Main Author: Ramalingam, Sanjiv
• Format: Others
• Published: UKnowledge 2007
• Subjects: Ventricular fibrillation|reentrant circuit|unidirectional block|alternans|anti-arrhythmic
• Online Access: http://uknowledge.uky.edu/gradschool_theses/442; http://uknowledge.uky.edu/cgi/viewcontent.cgi?article=1445&context=gradschool_theses

Ventricular fibrillation is one of the leading causes for Sudden Cardiac Death and is characterized by multiple activation wavefronts. Multiple activation wavefronts originate from a reentrant circuit which requires the presence of a unidirectional block in the path of a propagating excitation wave. It has been proposed that at the cellular level beat to beat alternation in the action potential duration at rapid pacing rates can result in a conduction block. Various mechanisms have been postulated to show the mechanisms of alternans. We use simulated activation in a one dimensional tissue fiber to show the existence of a new mechanism via which alternans can result. We used a new pacing protocol to eliminate alternans at the pacing site, and thus eliminating restitution of action potential duration at this site to reveal existence of alternans down the fiber. Effects on alternans of manipulations of specific ionic currents such as the sodium current (INa), calcium current (ICaL), potassium current (Ikr) and of the diffusion co-efficient (Dx) which simulates reduced expression of connexin 43 were determined. Decrease in sodium conductance, i.e. in excitability by half caused the alternans to occur at the pacing site itself even though APD restitution was eliminated. An increase or decrease in calcium current (ICaL) eliminated alternans throughout the fiber. The use of a novel pacing approach in investigation of alternans, as in this study, furthers our understanding of the mechanism of alternans and may prove helpful in the development of better anti-arrhythmic drugs in the future.