Most preclinical cardiovascular research is conducted on rodents and other small animal models. From a logistical, economic, reproducibility, and throughput perspective, it has obvious advantages. However, their phylogenetics, pathophysiological, and pharmacological responses are different from humans, and this may preclude the reliable translation to clinical use.
Taking advantage of our highly specialized surgical and endovascular skillset, we have focused on developing surgical and hybrid large animal models of common cardiac pathologies. This protocol is one good example of a simple, minimally invasive procedure that provides a good balance between reliability, reproducibility, and animal welfare. By monitoring the gradient in real-time using high-fidelity pressure sensors, we are able to accurately titrate the pressure gradient across the stenosis, resulting in a very homogeneous degree of severity between animals.
Furthermore, the minimally invasive approach results in a much lower complication rate and better animal recovery. The development of large animal models, in this case, swine, is promising for human-like pharmacological and device testing. This is particularly true for very sensitive areas where anatomy physiological similarities to humans are key, like anesthesia, cardiopulmonary bypass, ECMO, LVAS, percutaneous intracatheter therapies, and minimally invasive and robotic surgery.
To begin, identify the puncture site for arterial cannulation in an anesthetized pig. Using the vascular probe, identify the common femoral artery and confirm the position of the ultrasound marker and correct depth. Before assembling the introducer sheath, flush the introducer and dilator with heparinized saline.
Under ultrasound guidance, insert an echogenic arterial needle into the femoral artery. Once the arterial lumen is reached and pulsating arterial blood comes out from the needle hub, advance a J-tip guidewire into the artery. While maintaining pressure on the puncture site, remove the needle and advance the introducer and dilator assembly into the artery.
Next, remove the dilator and aspirate the blood from the side port of the introducer to confirm the correct positioning of the introducer. Sequentially, flush the introducer with sterile saline. Finally, connect an arterial pressure line to the side port of the femoral artery introducer to monitor blood pressure.
After performing arterial cannulation in an anesthetized pig, using the cardiac ultrasound transducer, locate the position of the ascending aorta. Then mark the incision site and disinfect the chest of the animal. Using a scalpel, make a two to three centimeter skin incision at the level of the 3/4th intercostal space.
Then dissect the underlying fascia and muscle layers, until the intercostal space is reached. Stop the ventilation without positive and expiratory pressure. Ensize the intercostal muscles to enter the thorax.
Then increase the incision to allow the placement of the retractor blades. Retract the ribs and visualize the underlying structures. Using minimally invasive cardiac surgery forceps and scissors, open the pericardium.
Then use wet sterile gauze to retract the left atria and any lung tissue covering the view of the aorta. Carefully separate the aorta from the pulmonary artery until the transverse pericardial sinus is reached. To facilitate aortic catheterization, place a radiopaque marker in the banding area.
Position the ePTFE graft or the nylon band around the ascending aorta. Connect a dual hemostasis valve adapter to a six French MP1 guide catheter and flush it with heparinized saline. Preload the guide catheter with a 260 centimeter 0.035 inch J-tip guide wire and introduce this assembly through the femoral arterial sheath.
Under fluoroscopic guidance, advance the guidewire and guide the catheter into the ascending aorta. When the aortic valve is identified, carefully cross it with a guidewire and introduce the guide catheter into the left ventricle. Check pressure traces to confirm left ventricle positioning.
Next, remove the guidewire, while leaving the guide catheter in the left ventricle. After aspirating the blood, flush the catheter with sterile saline and ensure no air bubbles are present in the catheter. After advancing two high-fidelity pressure sensors through the dual hemostasis valve adapter, pull the guide catheter back into the ascending aorta distally to the radiopaque marker, placed on the banding site.
While leaving one of the high-fidelity pressure sensors in the left ventricle, confirm the catheter position using pressure traces. After left ventricle catheterization, close the nylon band one click at a time, while closely monitoring pressures. Place sterile plastic tubing on the nylon band end to avoid accidental damage to the surrounding structures.
For ePTFENs constrict the band using 45 degree forceps. Monitor the pressure to estimate the relative location of the constriction. Finally, place a titanium hemoclip on the forceps position.
The use of high-fidelity pressure sensors enables obtaining high-quality pressure signals, allowing real-time and accurate calibration of the stenosis. Transthoracic echocardiography confirmed significant aortic stenosis immediately after surgery and during follow-up. Banding surgery resulted in significant aortic stenosis and left ventricular concentric hypertrophy.
Postmortem macroscopic analysis of the heart revealed larger hearts and a thicker left ventricular wall.
