Echocardiography Assessment of Cardiac Function and Pulmonary Hypertension in Lambs

Summary

This protocol describes echocardiography assessment of cardiac structure, function, and pulmonary hypertension in a lamb model of evolving bronchopulmonary dysplasia. The method enables serial evaluation of cardiopulmonary disease and may be applied to other large-animal models of neonatal and adult cardiovascular disease.

Abstract

Premature birth is strongly associated with cardiac dysfunction, including impaired ventricular function and altered cardiac structure, which can lead to progressive heart failure and other short- and long-term morbidities. However, the natural history of cardiac dysfunction in infants born prematurely is not well defined. In the lamb model of bronchopulmonary dysplasia with associated pulmonary hypertension (BPD-PH), lambs are delivered at 110–128 days gestation (full term is approximately 145 days) and mechanically ventilated. The lambs develop cardiopulmonary complications of prematurity, including alveolar simplification on lung histology, the hallmark of BPD, and signs of increased pulmonary vascular resistance on echocardiography, consistent with evolving BPD-PH. This article describes a protocol for serial assessment of cardiac morphometry and function by echocardiography in preterm and former preterm lambs (up to approximately two months postnatal age). The protocol was developed by adapting guidelines from the American Society of Echocardiography. Echocardiography is serially performed on intubated and moderately sedated lambs using a bedside ultrasound system. Atrial and ventricular dimensions, right and left ventricular function, and PH-related measurements are obtained at each echocardiographic assessment. Measurements are reproducible and correlate with clinical status. This echocardiography protocol for assessing cardiac structure and function in lambs enables characterization of BPD-PH and evaluation of therapeutic approaches.

Introduction

The lamb model of evolving bronchopulmonary dysplasia and pulmonary hypertension (BPD-PH) replicates both the developmental lung stage and clinical care setting experienced by preterm infants in the neonatal intensive care unit (NICU). In the lamb model of evolving BPD-PH, lambs are delivered across a range of gestational ages from 110 d gestation (late canalicular phase of lung development, equivalent to 22–24 weeks gestation) through term (145 d) and mechanically ventilated. Lambs are followed for up to six months for the development of cardiopulmonary disease. This model recapitulates pathophysiology and histopathology resulting from mechanical ventilation wi....

Protocol

All experimental procedures were performed in compliance with the animal handling and training standards of the University of Utah’s Institutional Animal Care and Use Committee.

1. Procedure setup

1. Position the lamb in a sling in the prone position.
2. Position the echocardiographer on the left side of the lamb for most echocardiographic views described in this protocol, unless otherwise noted.
3. Place the ultrasound machine toward the head of the sling setup so that the echocardiographer can interface with the controls using the left hand and hold the transducer in the right hand.
4. Use an....

Results

The majority of the standard views recommended in the American Society of Echocardiography (ASE) pediatric echocardiography guidelines can be obtained in lambs. The standard A4C view, A2C view, and A5C view including the LVOT can be visualized (Figure 2A–2C). The parasternal long-axis view including the LVOT is also feasible (Figure 2D). A full complement of parasternal short-axis views, including views at the level of the aortic valve, pulmonar.......

Discussion

Echocardiography offers a noninvasive method to assess cardiac structure, function, and PH in lambs, including preterm and former preterm lambs (up to approximately two months corrected for gestational age) with evolving BPD-PH. A critical aspect of echocardiography in neonatal lambs is the use of a standardized protocol based on established guidelines and the application of the same rigor and best practices for image acquisition and measurement used clinically in human infants.

Other investig.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Phased-array cardiac transducer	GE	H44901AB	12S-RS probe; 4.5–12.0 MHz
Sling for animal positioning	Made on site from heavy-duty fabric	N/A	Used to support lamb in prone position during imaging
Ultrasound gel	Parker Laboratories, Inc.	PLI 01-08	Aquasonic 100 ultrasonic transmission gel
Ultrasound imaging system	GE	H48232DM	Vivid iq Vet v208