We seek to provide a realistic animal model of acute pulmonary embolism in pigs. The model creates an opportunity to investigate pathophysiology of pulmonary embolism, but also to evaluate novel treatments. Furthermore, the model is well-suited for hands-on training for healthcare workers in interventional procedures.
The field of acute pulmonary embolism has undergone fundamental changes in recent years. Novel pharmacological, and especially interventional therapies, are being developed, and preclinical testing and development in a realistic, in vivo setting are needed. Previous in vivo models have used artificial materials, such as glue or plastic beads, to induce pulmonary embolism.
In this model, we use the pig's own blood to create autologous emboli, which are therefore similar in size, shape, and texture to those found in patients. The model is well-characterized in previous studies of pathophysiology and interventions. Evaluations have included invasive hemodynamic meshes, various imaging modalities, histology, and biochemistry.
As the pig has a similar anatomy of an adult human and the emboli and hemodynamic phenotype are similar to that of a patient with acute pulmonary embolism, the model is ideal for investigation of pharmacological and interventional treatments. To begin, unpack a cardiopulmonary oxygenation system and locate the non-heparin-coated polyvinyl chloride or PVC tubes. Cut seven of these tubes into pieces of approximately 30 centimeters in length and close one end of each PVC tube with large hemostat forceps.
Obtain an anesthetized animal, establish ultrasound-guided intravascular access, and infuse the venous sheaths with saline. For clot formation, first, pause the isotonic saline infusion on one of the venous sheaths and draw a total of 180 milliliters of blood from the sheath. Partition the drawn blood into six PVC tubes and close the top of each tube with another hemostat forceps.
Then, hang the tubes vertically for a minimum of three hours at room temperature. Next, flush saline through the sheath and restart the saline infusion. For insertion of 26F sheath, pause the infusion pump connected to the sheath in the right external jugular vein.
Insert a long extra stiff guidewire through the sheath. Advance the wire caudally through the upper central veins, the superior vena cava, the right atrium, and into the inferior vena cava guided by fluoroscopy. Then, slowly extract the sheath while observing via fluoroscopy that the guidewire remains in the inferior vena cava.
Using a sterile napkin, compress the entry point while retracting the sheath. Use the Seldinger technique to exchange the sheath for a 16 French dilator. Extend the skin incision if necessary upon encountering resistance to advance the sheath into the venous circulation under fluoroscopic guidance.
Employ the Seldinger technique again to exchange the 16 French dilator for a 26 French sheath. Slowly advance the sheath through the large veins until the radiopaque tip reaches the superior vena cava. Carefully retract the dilator and guidewire out of the pig, ensuring that the sheath remains in place.
Draw blood to confirm the sheath placement and flush with 60 milliliters of saline to ensure that the sheath is fully flushed. Then, place a stack of sterile napkins under the external end of the sheath and the sterile drape to elevate it above heart level. Reconnect the infusion pump and resume the saline infusion.
For assembling the embolus delivery device, unpack the rest of the cardiopulmonary oxygenation system under sterile conditions. From the auto transfusion set, locate the 10-centimeter-long silicone tube attached to the bottom of the cardiotomy container and the three-by-eight to one-by-four inch connector piece attached to the silicone tube. Then, cut the silicone tube into two equal-sized pieces and set aside the half without the connector for now.
After locating the quick prime line, cut it approximately 20 centimeters from the Luer lock end and attach the open end to the one-by-four inch end of the connector piece. Then, connect a three-by-eight inch piece to a one-to-two inch connector piece with the open end of the silicone tube to complete part A.For part B, attach the remaining half of the silicone tube to the distal end of the aortic perfusion cannula. Locate and attach any three-by-eight inch connector to a one-by-two inch connector with the open end of the silicone tube.
To evaluate the clot, retrieve one of the PVC tubes containing a fully formed embolus and gently place the embolus on a surgical napkin, discarding the supernatant. To induce acute pulmonary embolism, place a 1, 000-milliliter bag of isotonic saline into a pressure infusion bag. Insert an infusion set and inflate the pressure bag to at least 200 millimeters of mercury, but not beyond the recommended pressure.
Then, connect the part A of the embolus delivery device to the side port of the three-way stopcock, followed by connecting the last PVC tube to the open end of part A.Place one embolus in the tube and fill the system with saline. After attaching part B to the other end of the PVC tube, insert the embolus device into the 26 French sheath and open the pressurized saline flow for about five seconds to infuse the embolus. Finally, induce the emboli until the mean pulmonary arterial pressure has doubled from baseline or until all six emboli have been induced, and monitor the pig to ensure it remains stable for 30 minutes.
Pulmonary CT scans showed no signs of pulmonary embolism at baseline, but after induction, multiple emboli were visible, increasing the pulmonary obstruction percentage from 0 to 57.1%Necropsy revealed large autologous emboli in the pulmonary arteries.
