Confirmation of Myocardial Ischemia and Reperfusion Injury in Mice Using Surface Pad Electrocardiography

Summary

During murine myocardial ischemia/reperfusion surgery, correct placement of the occluding ligature is typically confirmed by visible observation of myocardial pallor. Herein, a method of electrocardiographically confirming ischemia and reperfusion, to supplement observed myocardial pallor, is demonstrated in male C57Bl/6 mice.

Abstract

Many animal models have been established for the study of myocardial remodeling and heart failure due to its status as the number one cause of mortality worldwide. In humans, a pathologic occlusion forms in a coronary artery and reperfusion of that occluded artery is considered essential to maintain viability of the myocardium at risk. Although essential for myocardial recovery, reperfusion of the ischemic myocardium creates its own tissue injury. The physiologic response and healing of an ischemia/reperfusion injury is different from a chronic occlusion injury. Myocardial ischemia/reperfusion injury is gaining recognition as a clinically relevant model for myocardial infarction studies. For this reason, parallel animal models of ischemia/reperfusion are vital in advancing the knowledge base regarding myocardial injury. Typically, ischemia of the mouse heart after left anterior descending (LAD) coronary artery occlusion is confirmed by visible pallor of the myocardium below the occlusion (ligature). However, this offers only a subjective way of confirming correct or consistent ligature placement, as there are multiple major arteries that could cause pallor in different myocardial regions. A method of recording electrocardiographic changes to assess correct ligature placement and resultant ischemia as well as reperfusion, to supplement observed myocardial pallor, would help yield consistent infarct sizes in mouse models. In turn, this would help decrease the number of mice used. Additionally, electrocardiographic changes can continue to be recorded non-invasively in a time-dependent fashion after the surgery. This article will demonstrate a method of electrocardiographically confirming myocardial ischemia and reperfusion in real time.

Introduction

Heart disease remains the leading cause of death worldwide^1,2. Not only is the left ventricle (LV) the most muscular chamber, responsible for pumping blood from the heart to the entire body³, it is a common cardiac injury site post-myocardial infarction⁴. Left ventricular tissue death often results in systolic heart failure. Animal models of heart disease are imperative for the advancement of biomedical cardiovascular research. The C57Bl/6 strain of mice have been a popular choice for animal models due to their quick breeding time, low cost and ease in genetic alterations. Most murine surgical models for the study of heart disease invo....

Protocol

All surgical procedures performed on animals should be carried out in accordance with Guide for the Care and Use of Laboratory Animals¹³ or other appropriate ethical guidelines. Protocols should be approved by the animal welfare committee at the appropriate institution before proceeding.

1. Preparing for the ECG

NOTE: Before beginning, don personal protective equipment including gloves, eyewear and a clean laboratory coat or disposable gown.

1. Clean the ECG pad using a non-alcohol and non-bleach based decontamination solution. Gently use a delicate task wipe to blot off excess solution to ens....

Results

A normal murine ECG is displayed in Figure 2 with alphabetic markers for electrical events P, Q, R, S, J and T. P is the initial atrial depolarization. QRS is the wave of depolarization over the ventricles. J is early repolarization and T represents heterogeneous repolarization also known as recovery¹¹. It should be noted that many labs do not use the J-wave nomenclature and instead refer to the SJT-segment as the ST-segment^10,15-17. Here, results an.......

Discussion

Using ECG changes as a supplemental method for confirming myocardial ischemia and reperfusion ensures the accurate placement of the occluding ligature. Accuracy of ligature placement is critical to reducing data variability among animals. The LAD in a mouse heart is a difficult artery to visualize. Therefore, supplementing visual pallor with electrocardiographic changes will help ensure the correct placement of the ligature and resulting tissue damage.

Since the ECG pad offers a non-invasive v.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Vevo 1100	Fujifilm Visual Sonics		Echocardiography Machine
Mouse Handling Plate	Fujifilm Visual Sonics		Heated ECG plate
Signa-Gel			Highly Conductive Multi-
Electrode Gel	Parker	15-25	Purpose Electrolyte
Transpore Medical Tape	3M	1527-0
PI-Spray II	Pharmaceutical Innovations	NDC 36-2013-25	Cleaning agent for ECG plate
C57Bl6 Mice	The Jackson Laboratory	000664	Male, 8 - 12 wk
IsoThesia-Isoflurane	Henry Schein	NDC 1169-0500-1
Excel	Microsoft
Systane Nighttime Lubricant Eye Ointment	Alcon	65050935
7-0 Perma-Hand Silk Sutures	Ethicon	640.O32
5-0 Perma-Hand Silk Sutures	Ethicon	K809.O32
Surgical Scissors	ROBOZ	RS-5881
Forceps	Fine Science Tools	11052-10
Gauze	Bio Nuclear Diagnostics Inc	DIS-022B
Needle Holder	Fine Science Tools	12565-14
Buprenex CIII	Patterson Veterinary	0-891-9756	Buprenorphine Hydrochloride Analgesic
Betadine	Purdue Products	67618-150-08
Nair	Church and Dwight Co.	NRSL-22339-05