Murine Echocardiography of Left Atrium, Aorta, and Pulmonary Artery

Summary

The following protocol describes the methodology for the acquisition and analysis of echocardiographic images used to obtain the Left Atrial Volume (LAV), Aorta (Ao) diameter, and Pulmonary Artery (PA) diameter in mice. This technique is a non-invasive, non-terminal procedure that allows assessment of the cardiopulmonary function.

Abstract

The present methodology teaches the investigator how to measure and use the LAV as a surrogate of chronic elevations in Left Ventricular diastolic pressure through echocardiography, as well as to obtain measurements of the Aorta and PA diameter in mice.

Mice older than 10 d of age can be analyzed using the present technique. The technique is composed of 3 main steps: set-up, image acquisition, and image analysis. The set-up step consists of getting the mouse anesthetized with 1% isoflurane, shaving it, and taping it in a supine position to a heated EKG board where the image acquisition will take place. The image acquisition step consists of learning to identify the cardiac structures and obtaining all the required images with its correspondent probe and axis in order to be able to calculate volumes and diameters. The image analysis step consists of measuring the previously acquired images with the aid of computer software.

Advantages of the proposed technique include a fast (15 min) procedure that would allow the researcher to evaluate interventions in a non-invasive, non-terminal approach and therefore follow the same mouse over time; each mouse can be used as its own control. This fact plus having the same operator perform all the acquisition and analysis for the entire experiment minimizes the limitation of operator-dependency. The present methodology is useful for mouse researchers in cardiovascular and pulmonary medicine.

Introduction

The present methodology teaches the investigator how to measure and use the LAV, Aorta diameter and PA diameter with 2D echocardiography in mice under isoflurane. Heart Failure with preserved Ejection Fraction (HFpEF) in elderly people affects up to 10% in those 80 years and older¹ and results in significant morbidity and mortality. Significant mortality also occur from Pulmonary Hypertension (PH), an insidious disease process presenting with similar symptoms as HFpEF, in which elevated pulmonary artery pressures lead to exertional dyspnea, progressive right heart failure, and often death.² The increasing prevalence of b....

Protocol

All animals were cared for in accordance with the guidelines of the National Institutes of Health Guide for the Care and Use of Laboratory Animals at Baylor College of Medicine.

1. Set-up

1. Turn on the echocardiographic system. Start the software by selecting "Cardiac Measurements" from the drop down menu displayed and click "Initialize".
2. To begin a new study click on the "New" button on the upper part of the screen and enter the demographic information of the mouse in study. For example mouse ID, sex, date of birth as well as the name of the operator doing the study.
3. Turn on the temperature-controlled EKG boar....

Results

Assessment of the LA volume and PA diameter with echocardiography allows the discrimination between models where increased pulmonary artery resistance results in increased PA diameter with no change in LAV from those where the Pulmonary Artery and Left Atrial enlargement are both a result of elevated filling pressures on the left side of the heart. Images displaying the differences in the two pathophysiologies are shown in Figure 4. Images of the LA and PA are from young,.......

Discussion

There are three critical steps to successfully measure the LAV, Aorta and PA diameters. During the Set-up it is important to completely remove the fur on the chest; failure to do so will result in interference with image quality. During the Image Acquisition steps it is important to obtain each image with their corresponding probe and filter as the frames per second vary from probe to probe: that is 25 MHz and Cardiac Filter for the assessment of the LAV and 30 MHz and Abdominal Filter for assessment of the Aorta and PA .......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Vevo 770 high-resolution in vivo micro-imaging system	Visual Sonics	Vevo 770-120	Echocardiographic Equipment
707B RMV (Real time MicroVisualization) 30 MHz Scanhead with encapsulated transducer	Visual Sonics	707B-256	Real Time Microvisualization Scanhead
710B RMV (Real time MicroVisualization) 25 MHz Scanhead with encapsulated transducer	Visual Sonics	710B-159	Real Time Microvisualization Scanhead
Vevo integrated rail system including physiological monitoring unit	Visual Sonics
Inhalation Anesthesia System	VetEquip	VE2627	Anesthesia System
Isofluorane	Henry Schein	50033
Electric razor	Wahl	General supply
Hair removal cream	Nair	General supply
Transductor cream	Parker
Transductor gel	Parker
Standard Gauze pads	McKeeson	General supply
Tape	Durapore	General supply
Nose cone			For anesthesia delivery
Water
Vet eye ointment	Puralube	General supply	To prevent dryness
Cotton tipped applicators		General supply
USB Flash Drive		General supply