Session P91.2

Cardiac Arrhythmias Induced by an Electrical Stimulation at a Cellular Level

S Jacquir*, S Binczak, D Vandroux, G Laurent,
P Athias, JM Bilbault

Université de Bourgogne
Dijon, France

Among the reentrant arrhythmias, our study focused on the fibrillation phenomenon, which is characterized by a high irregular excitation rate responsible for erratic atrial contractions (e.g., atrial fibrillation). The reentrant phenomenon is described as a wavefront that reenters and hence re-excites the same area repeatedly as opposed to the normal ‘planar’ wavefront emitted by the sinus node that depolarizes the myocardial tissue only once per cardiac cycle. During a fast fibrillatory rhythm, re-excitations occur at a rate higher than the normal sinus rhythm which in turn is, overdriven. Experimental evidence that functional reentrant spiral waves (SW) are present in rabbit cardiac atrial was first given by Allessie et al. (1973), and later on by Davidenko et al. (1990, 1992) and Pertsov et al. (1993). The idea that atrial or ventricular fibrillations are both caused by multiple chaotically wandering electrical wavelets leading to chaotic uncoordinated contractions, was first formulated by Moe et al. (1964). However, opinions differ on how these wavelets arise. According to the spiral breakup hypothesis, wavelets are the result of the fragmentation of an initial “mother” spiral wave (Panfilov & Pertsov, 2001; Weiss et al., 2002). According to the fibrillatory conduction hypothesis, wavelets are the result of a single excitation source (Jalife et al., 1998; Jalife, 2000; Zaitsev et al., 2000). This source emits waves at such a high frequency, that because of tissue heterogeneities, they cannot be conducted at a 1 to 1 ratio in all parts of the tissue. The aim of our investigation was to induce an experimental fibrillation phenomenon in order to identify, at a cellular level, the electrophysiological mechanism implicated in its initiation and perpetuation. In this article, we have described the method used and our preliminary results. First of all, we have studied spontaneous electrical activities of cultured neonatal rat cardiomyocytes using a Micro-Electrode Array (MEA) system. Field potentials (FP) corresponding to the extra-cellular potentials from a 2-4 cells area were recorded to approximate activation maps with one “electrical unit” resolution. Secondly, cardiomyocytes have been submitted to a high frequency burst stimulation which was applied at the edge of the MEA. This high rate stimulation was able to induce fast and irregular electrical activities which mimicked fibrillation patterns. These fibrillation waves were analyzed more precisely by reconstructing an electrical activation map. Several spiral waves (3 ± 1 SW per episode) were observed during induced arrhythmias. Within the surface mapped, SW appeared to be random and the pattern could change from one “beat” to another. SW were also unstable in location, moving randomly inside or outside the recording area.

(Abstract Control Number: 97)