Optimization of Transesophageal Atrial Pacing to Assess Atrial Fibrillation Susceptibility in Mice

Summary

The present protocol describes the optimization of experimental parameters when using transesophageal atrial pacing to assess atrial fibrillation susceptibility in mice.

Abstract

Mouse models of genetic and acquired risk factors for atrial fibrillation (AF) have proven valuable in investigating the molecular determinants of AF. Programmed electrical stimulation can be performed using transesophageal atrial pacing as a survival procedure, thus enabling serial testing in the same animal. However, numerous pacing protocols exist, which complicates the reproducibility. The present protocol aims to provide a standardized strategy to develop model-specific experimental parameters to improve reproducibility between studies. Preliminary studies are performed to optimize the experimental methods for the specific model under investigation, including age at the time of the study, sex, and parameters of the pacing protocol (e.g., mode of pacing and definition of AF susceptibility). Importantly, care is taken to avoid high stimulus energies, as this can cause stimulation of the ganglionic plexi with inadvertent parasympathetic activation, manifested by exaggerated atrioventricular (AV) block during pacing and often associated with artifactual AF induction. Animals demonstrating this complication must be excluded from the analysis.

Introduction

Atrial fibrillation (AF) represents a final common pathway for multiple acquired and genetic risk factors. For studies investigating the pathophysiologic mechanisms of the AF substrate, mouse models are advantageous given the ease of genetic manipulation and the fact that, in general, they reproduce the AF susceptibility observed in humans for different clinical phenotypes^1,2,3. However, mice rarely develop spontaneous AF⁴, necessitating the use of provocative atrial pacing studies.

Programmed electrical stimulation (PES) ca....

Protocol

This procedure was approved by the Vanderbilt Institutional Animal Care and Use Committee and is consistent with the Guide for the Care and Use of Laboratory Animals. The protocol was developed using both genetic⁹ and acquired¹⁰ (e.g., hypertension) mouse models of AF susceptibility. The operator was blinded to the phenotype of the mouse under study.

1. Animal selection

1. For genetic models, subject mice to biweekly (i.e., every other week) atrial pacing as described below (see step 6.) to determine the optimal period of AF susceptibility.
   1. Begin biweekly ....

Results

Transesophageal atrial pacing studies assess the electrophysiologic properties of the SA and AV nodes by determining the SNRT and AVERP, as well as AF susceptibility⁶ (Figure 1). ECG recording enables measurements of P wave duration, PR interval, QRS duration, and QT/QTc intervals. Continuous recording of the ECG during rapid atrial pacing can provide the following measurements of AF vulnerability: the number of episodes induced during the study, cumulative and averag.......

Discussion

Transesophageal atrial pacing not only allows serial studies in the same animal, but its duration is typically shorter than intracardiac studies (~20 min), thus minimizing anesthetic use and its effects on electrophysiologic parameters.

It is critical to optimize the methods initially for each individual mouse model. Aging increases AF inducibility in normal mice^18,19, and individual genetic models may demonstrate AF inducibility over.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
27 G ECG electrodes	ADInstruments	MLA1204
2-F octapolar electrode catheter	NuMED	CIBercath
Activated carbon canister	VetEquip	931401
Analysis software	ADInstruments	LabChart v8.1.13
Biological amplifier	ADInstruments	FE231
Data acquisition hardware	ADInstruments	PowerLab 26T
Eye ointment	MWI Veterinary	NC1886507
Heating pad	Braintree Scientific	DPIP
Isoflurane	Piramal	66794-017-25
Stimulator	Bloom Associates	DTU-210
Stimulus Isolator	World Precision Instruments	Model A365