Optical Mapping Analysis of the Spatiotemporal Pattern of Experimental Tachyarrhythmia in Improved Isolated Rat Atrium Preparation

Abstract

Abstract:We have studied the experimental tachyarrhythmia in an improved isolated rat atrial preparation for the optical mapping of excitation spread. The atrial preparation, including the right or left auricle, was dissected from the adult rat heart, and an artificial hole was made in the center of the preparation. The preparation was then stained with a fast merocyanine-rhodanine voltage-sensitive dye (NK2761). Using a multi-element (16 × 16) photodiode array, the spread of excitation was assessed optically by timing the initiation of the action potential-related extrinsic absorption changes. In comparison with the intact isolated right atrial preparation, which we used previously, the mapping of the excitation spread was much easier and more precise because of the simple structure of the preparation. The electrical stimulation applied by a bipolar electrode evoked the sustained excitation with a fast rhythm, which we termed "experimental tachyarrhythmia" (ET). We optically mapped the spatiotemporal patterns of the spread of excitation during the initiation and the maintenance phases of ET. In most cases, a rotation of the excitatory wave around the artificial hole, i.e., a circus movement of the excitatory wave, was observed. These maps suggest that this circus movement resembles the basic mechanism of the tachycardia-like excitation observed in the intact isolated right atrial preparation. On the other hand, the appearance of an ectopic pacemaker with a fast rhythm was also observed. In some examples, two ectopic pacemakers appeared simultaneously. We consider that the experiment using the improved preparation is a superb in vitro model of atrial arrhythmia.Key words: rat atrium, voltage-sensitive dye, multiple-site optical recording, circus movement, ectopic pacemaker.To elucidate the basic mechanism(s) of atrial arrhythmia, we have been carrying out experiments using optical methods for monitoring membrane potential activity using fast voltage-sensitive dyes [1,2]. We optically mapped the spread of excitation in the intact isolated rat right atrial preparation during an abnormal state of atrial rhythm, which we termed "tachycardia-like excitation", evoked by electrical stimulation [3][4][5]. During this event, the occurrence of the excitatory waves shows a much faster rate than that in the normal condition, and the physiological pacemaker does not work. From the optical mapping, we demonstrated that the reentry mechanism took part in tachycardia-like excitation. In the most cases, the excitatory wave rotated around an anatomical obstacle (mostly the ostium of the superior vena cava). Moreover, in some examples, abnormal automatism, i.e., an ectopic pacemaker, also took part in the generation of tachycardia-like excitation. This phenomenon is interesting because transient complex patterns of excitation spread were observed during the initiation phase of the event before the establishment of the stable reentry pattern. Furthermore, event-to-event variations were observed in the excitation spread pattern. Thi...

Optical mapping study of blebbistatin-induced chaotic electrical activities in isolated rat atrium preparations

“…The right or left auricle preparation was incised. The preparation was attached, positioning the endocardial side upward, to the silicone (KE106LTV; Shin-etsu Chemical, Tokyo, Japan) bottom of a simple chamber by pinning with tungsten wires, as described previously [3,4,6]. Preparations did not include the physiological pacemaker, and they did not exhibit spontaneous excitation.…”

“…Optical measurement An optical recording system, designed to record the absorption change of NK2761 as an action potential-related optical signal, equipped with a 16 9 16-element photodiode array was used [4,6]. In this system, the preparation chamber was mounted on the stage of a microscope (FLUOPHOTO-VFD; Nikon, Tokyo, Japan).…”

“…The results enabled optically mapping of the spread of excitation in isolated rat atrial preparations during an abnormal state of atrial rhythm evoked by electrical stimulation [3][4][5][6]. Excitatory waves occurred at a much faster rate during this abnormal state than in the normal condition, and the physiological pacemaker did not function.…”

“…In order to reduce contraction-related optical signals, we used mechanical stretching as well as 2,3-butanedione monoxime (BDM: 20 mM) or cytochalasin D (Cyto D: 20-40 lM) [3][4][5][6][7]. These chemicals inhibit muscle contraction while having little effect on the electrical activities of the cardiac muscle.…”

The Photodiode Array: A Critical Cornerstone in Cardiac Optical Mapping

“…Investigators have successfully used optical surface recordings to determine wavefront orientation beneath the surface (Hyatt et al, 2005;Zemlin et al, 2008), and also to interrogate deeper layers of tissue using transillumination methods (Baxter et al, 2001) and deeper-penetrating, near-infrared fluorescing dyes (Matiukas et al, 2006;Matiukas et al, 2007;Salama et al, 2005). Photodiode sensors were used in some of the earliest optical recordings of cardiac APs (Morad & Salama, 1979;Salama, 1976), and continue to be used today (Cheng, 2006;Sakai, 2008). Photodiodes function by transferring incoming photonic energy to bound electrons in a semi-conductive material in a transistor configuration.…”