New insights into the atrial electrophysiology of rodents using a novel modality: the miniature-bipolar hook electrode

Abstract

(EP) in rodents are challenging, and available data are sparse. Herein, we utilized a novel type of bipolar electrode to evaluate the atrial EP of rodents through small lateral thoracotomy. In anesthetized rats and mice, we attached two bipolar electrodes to the right atrium and a third to the right ventricle. This standard setup enabled high-resolution EP studies. Moreover, a permanent implantation procedure enabled EP studies in conscious freely moving rats. Atrial EP was evaluated in anesthetized rats, anesthetized mice (ICR and C57BL6 strains), and conscious rats. Signal resolution enabled atrial effective refractory period (AERP) measurements and first time evaluation of the failed 1:1 atrial capture, which was unexpectedly longer than the AERP recorded at near normal cycle length by 27.2 Ϯ 2.3% in rats (P Ͻ 0.0001; n ϭ 35), 31.7 Ϯ 8.3% in ICR mice (P ϭ 0.0001; n ϭ 13), and 57.7 Ϯ 13.7% in C57BL6 mice (P ϭ 0.015; n ϭ 4). While AERP rate adaptation was noted when 10 S1s at near normal basic cycle lengths were followed by S2 at varying basic cycle length and S3 for AERP evaluation, such rate adaptation was absent using conventional S1S2 protocols. Atrial tachypacing in rats shortened the AERP values on a timescale of hours, but a reverse remodeling phase was noted thereafter. Comparison of left vs. right atrial pacing in rats was also feasible with the current technique, resulting in similar AERP values recorded in the low right atrium. In conclusion, our findings indicate that in vivo rate adaptation of the rodent atria is different than expected based on previous ex vivo recordings. In addition, atrial electrical remodeling of rats shows unique remodelingreverse remodeling characteristics that are described here for the first time. Further understanding of these properties should help to determine the clinical relevance as well as limitations of atrial arrhythmia models in rodents.atrial effective refractory period; rate adaptation; electrical remodeling MICE AND RATS ARE USED EXTENSIVELY in cardiac research, and reliable models of cardiac pathologies have been developed and applied in these species (4,19,31). Moreover, genetically altered mice have become invaluable tools for studying the molecular basis of cardiac pathologies including ventricular arrhythmias (7, 28). Use of rodents for studying atrial arrhythmias has been largely limited, but in recent years atrial tachyarrhythmias have been repeatedly produced in rats and mice, and rodents are increasingly used for studying various molecular, cellular, and pharmacological aspects of atrial function (1,5,8,24,36,37). In addition, mice with genetic alterations are providing important insights in this field as well (17,23,27,32).Due to the small size of the rodent heart and, more so, the rodent atria, electrode implantation for studies of functional electrophysiology is challenging. Several techniques were developed to increase the applicability of such studies (2, 23). The transesophageal approach, which is least invasive, necessitates the use of high e...

Speckle-Tracking Echocardiography Elucidates the Effect of Pacing Site on Left Ventricular Synchronization in the Normal and Infarcted Rat Myocardium

“…The implantable device that was used to pace the heart at different locations was originally designed for long-term atrial pacing and recording in freely moving rats [16]. In this device, the electrical connections to the epicardial surface are achieved using miniature-bipolar hook electrodes, which have been described in detail previously [16].…”

“…In this device, the electrical connections to the epicardial surface are achieved using miniature-bipolar hook electrodes, which have been described in detail previously [16]. The specific design of the miniature-bipolar hook electrode allows it to be positioned on a desired location on the epicardial surface of the atria or ventricles through a small lateral thoracotomy without the need of additional suturing [16]. The implantable device consists of an 8-pin 'female' connector that is attached by flexible insulated electrical wires to a set of two miniature bipolar hook electrodes (Figure 1a).…”

“…Following chest closure, each animal was placed in a prone position and the back connector was exteriorized through the skin of the back ( Figure 1B). Postoperative recovery and analgesia were done as described previously [16].…”

“…During BIV pacing, two independent isolation units were used for simultaneous but independent RV apical and LV pacing. A program developed by YE [16] was used to control data acquisition, electrical stimulation and off-line analysis. QT interval measurements were manually done off-line on the digital signals under high time and voltage magnification scales.…”

“…In the present study, using an implanted device that was developed for pacing and recordings in conscious rodents [16], we acutely evaluated the effect of pacing site on LV synchronization in normal and infarcted rats following post operative recovery. We hypothesized that the mechanical effects of LV pacing and BIV pacing should be favorable compared to RV pacing.…”