The protocol describes three reproducible techniques for delivering cardioactive drugs to porcine subjects. It is of great interest to translational scientists pursuing novel biological approaches to cardiac repair following myocardial infarction. In this video, drug delivery is demonstrated via intramyocardial injection following surgical exposure of the heart.
This technique allows accurate drug delivery under direct vision, and is associated with high local retention of the delivered product. Demonstrating the procedure today with me will be Juntang Lu, a veterinary surgeon from our lab. Assisting him will be Dr.Alan Marcus, veterinary anesthetist, Dr.Sally Kim, Samuel Turnbull and Mr.Vu Tran.
Begin thoracotomy and epicardial cell injection by administering intravenous prophylactic antibiotics and continue it every 90 minutes throughout the procedure. Position the animal in the right lateral recumbency position and apply a 100 micrograms per hour fentanyl patch to the flat plane behind the pig's ears. Cover it with an adhesive dressing or 2-0 suture.
Set up the electroanatomic mapping system, cabling, and patches following the product specifications. Before marking a 10 centimeter horizontal line between ribs four and five on the animal. Prepare a mixture of lidocaine and bupivacaine in a syringe with a 25 gauge needle and perform the cutaneous line block procedure on an aseptically prepared surgical site as described in the manuscript.
After draping the animal, make a 10-centimeter skin incision along the marked line using a number 22 scalpel. Using monopolar cautery, deepen the incision through the underlying muscle layers until the intercostal muscles have been reached. Prepare a sterile syringe of bupivacaine and lignocaine.
Attach a 25 gauge needle and insert the needle on the caudal edge of the fourth rib. Slowly inject a quarter of the syringe's volume without passing the needle through the intercostal vein or artery. Repeat this at three more locations along the caudal edge of the fourth rib.
After confirmation from the anesthetist, incise the intercostal muscles carefully using the Metzenbaum scissors. Ensure to turn off the ventilator and incise the pleura. After the incision has been made, turn the ventilator back on and adjust the positive and expiratory pressure to four centimeters of water.
Place the self retaining rib retractors between the ribs and open them slowly to expose the heart. Using tissue forceps, gently grasp the pericardium and incise with Metzenbaum scissors to exteriorize the heart. Place temporary 2-0 stay sutures at both ends and sides of the pericardial incision to fix it to the thoracic wall.
Create a pericardial well, ensuring the sides of the pericardium are supported to render the pericardial well as shallow as possible. Once done, pack the region surrounding the heart using moistened swabs or laparotomy sponges to prevent the drying of exposed tissues. Next, deliver the apex of the heart from within the pericardial cavity with an index finger behind the left ventricle.
Take care to minimize left ventricular compression. Return the heart immediately to the pericardial cavity and take the necessary steps to improve hemodynamic parameters before further dislocation. Use an electrophysiological mapping catheter and create an electroanatomic voltage map of the left ventricular epicardial surface.
Identify scar, border, and remote zones by standard voltage cutoffs. Bend the needle of the 27 gauge therapeutic delivery syringe to roughly an 80 to 90 degree angle and advance the needle into the target tissue at a shallow angle. Apply pressure to the syringe plunger to discharge one fourth to one third of the total volume.
Annotate the injection site location on the generated epicardial voltage map using the electrophysiological mapping catheter. Partially withdraw the needle, redirect it within the myocardium, and discharge another one fourth to one third of the volume of the syringe. Repeat this to deliver the desired dose.
Next, remove the swabs packing off the heart and gently remove the sling under the heart so it returns to its neutral position. Remove the 2-0 stay sutures from the pericardium before relaxing and removing the retractor from the thorax. Close the thorax by placing size one polydioxanone sutures, or PDS, through the spaces between ribs three and four and ribs five and six using a blunt-tipped round needle.
Insert a short silicone tubing into the ventral edge of the incision before tightening and tying off the rib-approximating sutures. Place the free end of the tubing into a bowl of sterile saline for underwater sealed drainage of the pleural cavity. To expel the free air from the thorax, turn the ventilator onto the free breathing setting.
Use the reservoir bag on the rebreathing circuit to provide consistent positive pressure to the airways and continue this pressure until bubbling is no longer observed in the saline bowl. Then remove the silicone tube. Then close the overlying muscle layers in the simple continuous pattern with 2-0 absorbable sutures, and close the skin in a simple continuous pattern with a 2-0 or 3-0 non-absorbable suture.
Finally, apply an adhesive dressing to the surgical site and place scattered simple interrupted sutures to assist in keeping the dressing in place. Out of 29 animals that underwent thoracotomy and epicardial injection, 26 survived. Histological analysis confirmed that the human cell engraftment was successful in all these surviving animals.
Careful and gentle handling of the heart by the surgeon, along with stringent observation of hemodynamic parameters by the anesthetist are critical to ensuring safety for this procedure. Use of vasopressor drugs may be required to correct any transient hemodynamic instability. This reproducible protocol facilitates reliable intramyocardial drug delivery and can be tailored to suit individual study designs.
