Echocardiographic Assessment of the Right Heart in Mice

Summary

This article provides a protocol for the echocardiographic assessment of right ventricular size and pulmonary hypertension in mice. Applications include phenotype determination and serial assessment in transgenic and toxin-induced mouse models of cardiomyopathy and pulmonary vascular disease.

Abstract

Transgenic and toxic models of pulmonary arterial hypertension (PAH) are widely used to study the pathophysiology of PAH and to investigate potential therapies. Given the expense and time involved in creating animal models of disease, it is critical that researchers have tools to accurately assess phenotypic expression of disease. Right ventricular dysfunction is the major manifestation of pulmonary hypertension. Echocardiography is the mainstay of the noninvasive assessment of right ventricular function in rodent models and has the advantage of clear translation to humans in whom the same tool is used. Published echocardiography protocols in murine models of PAH are lacking.

In this article, we describe a protocol for assessing RV and pulmonary vascular function in a mouse model of PAH with a dominant negative BMPRII mutation; however, this protocol is applicable to any diseases affecting the pulmonary vasculature or right heart. We provide a detailed description of animal preparation, image acquisition and hemodynamic calculation of stroke volume, cardiac output and an estimate of pulmonary artery pressure.

Introduction

Elevated pulmonary pressure and right ventricular (RV) dysfunction are the hallmarks of pulmonary vascular disease in animal models and human patients with pulmonary arterial hypertension (PAH). Transgenic and toxic (e.g. monocrotaline or hypoxia) models of PAH are widely used to study the pathophysiology of PAH and to investigate potential therapies. Given the expense and time involved in creating animal models of disease, it is critical that researchers have tools to accurately assess phenotypic expression of disease.

Echocardiography is the mainstay of the noninvasive assessment of ventricular function in rodent models^1,2

Protocol

1. Equipment Preparation 

1. Examine the ultrasound transducer for defects. Depending on the equipment used, this step may be unnecessary.
   1. If an air bubble is observed, remove the screw located on the right side of the transducer head, and add sterile water through the hole with a 26 G needle. Air bubbles inside the transducer head are common. They will impede the acquisition of quality images.
   2. Check the membrane covering the probe for leaks or holes. Replace if necessary.
2. Open the software and initialize the probe.
   1. Choose the cardiac package from the drop down menu, along with the appropriate tr....

Results

The principal goals of this protocol are to quantify RV size and function, and to understand the degree to which the pulmonary vasculature is diseased. Appropriate preparation of both the mouse and echocardiography equipment is essential to obtaining accurate and reproducible results. Mice should have their chest depilated and limbs secured to the imaging platform with tape. Anesthesia, in this case isoflurane, is administered via nose cone. The transducer should be checked for defects, particularly air bubbles, which ca.......

Discussion

Mouse models of disease, either transgenic or toxin-related, require phenotypic validation that the model actually recapitulates the human disease it is intended to emulate. This validation can often be accomplished by the presence or absence of a particular feature, for example development of a tumor. However, models that result in hemodynamic abnormalities such as aortic constriction models of left ventricular hypertrophy or our transgenic model of PAH are more difficult to validate. These models require either termina.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Vevo 770 High Resolution Micro-Ultrasound System	Visualsonics Inc.		get more info at www.visualsonics.com/products
RMV (Real-Time MicroVisualization) 704B 40 mH Scanhead w/ Encapsulated Transducer	Visualsonics Inc.		get more info at www.visualsonics.com/products
Vevo Integrated Rail System including the Physioogical Monitoring System	Visualsonics Inc.		get more info at www.visualsonics.com/products
Computer Monitor set up for use with the Vevo770	DELL or other General Supplier
Computer Mouse set up for use with the Vevo770	General Supplier
Vevo770 Cardiac Package Software	Visualsonics Inc.		get more info at www.visualsonics.com/products
VetEquip Portable Tabletop Anesthesia Machine with an Isoflurane Vaporizer	VetEquip		get more info at vetequip.com
Activated Charcoal Waste Gas Containers	VetEquip/Vaporguard	931401	get more info at vetequip.com
Puralube Eye Ointment	Henry Schein		get more info at henryschein.com
Ecogel 100 Ultrasound Gel	EcoMed Pharmaceuticals	30GB	get more info at ecomed.com
3M Transpore Tape	Fisher Scientific	1527-0	get more info at fishersci.com
Small Flathead Screwdriver	General Supplier
Sterile H2O	DDI H2O from faucet and then autoclave
6 in Cotton Tipped Applicators	Fisher Scientific		get more info at fishersci.com
Nair (depilatory cream)	General Supplier
2 in x 2 in Gauze Sponges	Fisher Scientific		get more info at fishersci.com