The protocol is significant because it allows high-fidelity cardiac functional monitoring in large animal models for the preclinical evaluation of cardiovascular therapeutics. The main advantage of the technique is to make it possible for the procedures such as recording echocardiograms in awake pigs without using anesthetics. Demonstrating the procedure will be Greg Brown, co-designer, Pia Balmaceda, postdoc fellow, and Thuy Ha, specialist from Nora Eccles Harrison Cardiovascular Research and Training Institute.
Start with the stock three-shelf, pre-made heavy duty utility cart with locking wheels. Saw off the front and back of the cart. Then, replace them with 1.25-inch PVC pipe and chain link gates.
Reinforce the cart with metal bars on the undersides to maintain the cart's integrity. Make a hole on the top of the cart large enough to accommodate a hand holding an ultrasound probe. Place a plastic cover fitted to the aperture.
Create a reinforced metal ramp for mounting and dismounting using aluminum stock. Add removable rubber padding for grip using bolts and grommets. Insert 12-inch-long, 3/8-inch pins into left-and right-side PVC hinge mechanisms Notch side rails to enable width settings for the side gates to improve restraint and prevent the animal from turning around.
For training the pigs to eat from the trough, fill it with frozen treats and prolong the pigs'standing time. Use combinations of foods such as juice, meal replacer drink, yogurt with cereal, and standard chow, biscuits, and fruit bars. Normal meals may be withheld and fed in the trough during the echocardiography period instead.
Prior to eating from the contraption, introduced the pigs to frozen treat troughs on the ground to encourage the recognition of the trough as a high-value treat provider. To train the pigs to accept standing echocardiograms, start by introducing the pig to the cart by surrounding the cart with high-value treats for one to two days. Introduce the pig to the ramp by placing treats along the ramp for a couple of days.
Provide additional rewards when a pig walks up the ramp. Provide the frozen treat troughs at the front gate for two to three days. Allow the pig to stand on the cart without engaging its side restraints or gates.
In a couple of days, place the ultrasound probe with gel on the pig to help it get accustomed to the probe contact. To obtain echocardiogram images, take images of the parasternal imaging planes from the sides of the cart to the right and left axillae. Apical view, B-mode, and M-mode images can be obtained by probing through the cart floor to the subxiphoid region.
Short-axis, transverse-view, M-mode images were obtained through the cart sides to analyze the left ventricular internal diameter in systole and diastole and subsequent ejection volume calculation. The ejection fraction generated from sedated echo sessions was lower than from conscious sessions. Parasternal long-axis view B-mode images were used to calculate the ejection volumes with the area/length method.
The ejection fractions in both sedated and conscious sessions were similar. An important thing to remember is that the cart should be built with the growing sizes of animals in mind. Individualization of the food mixture can help improve acclimation.
The cart can facilitate other procedures, including blood drawn from implanted ear vein catheters, electrocardiogram recording, and other ultrasound-based monitoring such as abdominal ultrasound. This technique provides researchers an opportunity to obtain high-fidelity key physiological data from awake pigs used for studies of various human diseases.
