Fetal Mouse Cardiovascular Imaging Using a High-frequency Ultrasound (30/45MHZ) System

Summary

High-frequency ultrasound imaging of the fetal mouse has improved imaging resolution and can provide precise non-invasive characterization of cardiac development and structural defects. The protocol outlined herein is designed to perform real-time fetal mice echocardiography in vivo.

Abstract

Congenital heart defects (CHDs) are the most common cause of childhood morbidity and early mortality. Prenatal detection of the underlying molecular mechanisms of CHDs is crucial for inventing new preventive and therapeutic strategies. Mutant mouse models are powerful tools to discover new mechanisms and environmental stress modifiers that drive cardiac development and their potential alteration in CHDs. However, efforts to establish the causality of these putative contributors have been limited to histological and molecular studies in non-survival animal experiments, in which monitoring the key physiological and hemodynamic parameters is often absent. Live imaging technology has become an essential tool to establish the etiology of CHDs. In particular, ultrasound imaging can be used prenatally without surgically exposing the fetuses, allowing maintaining their baseline physiology while monitoring the impact of environmental stress on the hemodynamic and structural aspects of cardiac chamber development. Herein, we use the High-Frequency Ultrasound (30/45) system to examine the cardiovascular system in fetal mice at E18.5 in utero at the baseline and in response to prenatal hypoxia exposure. We demonstrate the feasibility of the system to measure cardiac chamber size, morphology, ventricular function, fetal heart rate, and umbilical artery flow indices, and their alterations in fetal mice exposed to systemic chronic hypoxia in utero in real time.

Introduction

Congenital malformations of the heart are heterogeneous structural defects that occur during early cardiac development. Current technical advances of operational procedures have led to significant improvements in the survival rates of infants with CHDs^1,2. However, quality of life is often compromised secondary to prolonged hospitalization and needs for staged surgical repair procedures^1,2,3,4,5. Prenatal detection of the underlying molecu....

Protocol

The University of California, Los Angeles, Animal Care and Use Committee has approved all procedures shown in this protocol. The experiments were conducted as part of an ongoing study under active animal protocols approved by the institutional Animal Care and Use Committee of University of California, Los Angeles, California, USA. Animal handling and care followed the standards of the Guide for the Care and Use of Laboratory Animals.

1. Preparing the High Frequency Ultrasound Imaging System

1. Turn on the ultrasound imaging system and the physiology monitoring unit.
2. Connect the 30/45 MHz transducer.
3. Place the co....

Results

Statistical analyses of cardiac and hemodynamic indices were performed offline. The means of 5 consecutive measurements in 3 optimal images were calculated. The data were expressed as Mean ± SEM. Student's t-test was used to infer intergroup comparisons. A P value of ≤0.05 was considered statistically significant.

Following the above protocol, we characterized the impact of chronic exposure to prenatal hypoxia .......

Discussion

Cardiovascular malformations and diseases are substantially influenced by genetic factors and environmental elements¹⁹. We have previously demonstrated a significant impact of maternal caloric restriction, initiated during the second trimester, on feto-placental circulatory flow and fetal cardiac function⁹.

Prenatal hypoxia is another common stress factor during fetal development that may tremendously affect the feto-placental physiology and .......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Vevo 2100	VisualSonics, Toronto, Ontario, Canada	N/A	High Freequency Ultrasound Biomicroscopy. The set up is available in animal physiology core facility, division of molecular medicine, UCLA. USA
inbred mice (c57/BL6)	Charles River Laboratories	N/A	Inbread wild type mouse strain