Quantification of Biventricular Function and Morphology by Cardiac Magnetic Resonance Imaging in Mice with Pulmonary Artery Banding

Summary

To understand the pathophysiology of right ventricular (RV) adaptation to abnormal loading, experimental models are crucial. However, assessment of RV dimensions and function is complex and challenging. This protocol provides a method to perform cardiac magnetic resonance imaging (CMR) as a noninvasive benchmark procedure in mice subjected to RV pressure load.

Abstract

Right ventricular (RV) function and failure are major determinants of outcome in acquired and congenital heart diseases, including pulmonary hypertension. Assessment of RV function and morphology is complex, partly due to the complex shape of the RV. Currently, cardiac magnetic resonance (CMR) imaging is the golden standard for noninvasive assessment of RV function and morphology. The current protocol describes CMR imaging in a mouse model of RV pressure load induced by pulmonary artery banding (PAB). PAB is performed by placing a 6-0 suture around the pulmonary artery over a 23 G needle. The PAB gradient is determined using echocardiography at 2 and 6 weeks. At 6 weeks, the right and left ventricular morphology and function is assessed by measuring both end-systolic and end-diastolic volumes and mass by ten to eleven cine slices 1 mm thick using a 9.4 T magnetic resonance imaging scanner equipped with a 1,500 mT/m gradient. Representative results show that PAB induces a significant increase in RV pressure load, with significant effects on biventricular morphology and RV function. It is also shown that at 6 weeks of RV pressure load, cardiac output is maintained. Presented here is a reproducible protocol for the quantification of biventricular morphology and function in a mouse model of RV pressure load and may serve as a method for experiments exploring determinants of RV remodeling and dysfunction.

Introduction

Patients with acquired and congenital cardiovascular diseases, including pulmonary hypertension (PH), are at risk of right ventricular (RV) dysfunction and failure¹. RV adaptation as a result of increased pressure load is characterized by concentric hypertrophy in early stages and progressive dilatation in end-stage disease. Furthermore, it is associated with disorders in metabolism and the extracellular matrix, processes of inflammation and, eventually, RV failure^2,3,4,5,6. Animal m....

Protocol

All experiments and animal care are conducted according to the Dutch Animal Experimental Act and conform to the Guide for the Care and Use of Laboratory Animals published by the US National Institutes of Health. The Animal Experiments Committee of the University of Groningen, the Netherlands, approved the current experimental protocol (permit number: 2014-041/3005).

1. Housing and acclimatization

1. Use 20–30 g wild type C57 black 6 (C57BL/6) mice (institutional breeding line described previously⁴⁷), male and female, all more than 8 weeks old. House the mice in groups with a maximum of five per cage. I....

Results

Mortality rate of the PAB surgical procedure is around 10%. The presented results show characteristics of mice in the sham (n = 5) and PAB (n = 8) groups. As shown in Figure 3, PAB gradient values significantly increased compared to sham animals at 2 and 6 weeks after PAB. This increase of loading caused RV dilatation expressed as increased RV, EDV, and RV ESV (Figure 4A,B). RV dysfunction occurred as RV EF decreased (Figure.......

Discussion

This protocol provides a reproducible method for PAB in mice and the subsequent assessment of cardiac remodeling and functional adaptation using CMR.

PAB differs from other models of increased RV pressure load because it involves absolute and static increase of afterload without the presence of other triggers. RV pressure load in models of hypoxia, monocrotaline, shunt, or a combination of these inducers are based on remodeling of the pulmonary vasculature. This remodeling is driven by endothe.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
14.0 MHz i13L-echocardiography transducer	GE Healthcare, Waukesha, WI, USA
20G cannula
23G needle
9.4T magnetic resonance scanner with 1,500 mT/m gradient set	Bruker BioSpin, Ellingen, Germany
Anesthesia induction chamber
Blunt 25G needle
Buprenorphine
Chloride-hexidine
CMR post-processing software	Medis Medical Imaging Systems, Leiden, The Netherlands		Qmass version 7.6
Data visualisation and statistical software	GraphPad Prism Inc, La Jolla, CA, USA		software version 7.02
Echocardiography machine	GE Healthcare, Waukesha, WI, USA		Vivid Dimension 7
Eye ointment
Heat mat
Incubator (37°C)
Isoflurane
Isoflurane evaporator
Miniventilator for rodents	Hugo Sachs	model 687
monofilament polypropylene 5-0 sutures
monofilament polypropylene 6-0 sutures
Needle and syringe for subcutaneous injections
Pediatric electrocardiogram-stickers
pure polyglycolic acid 5-0 sutures
Sterile surgical instruments
Ventilation mask