The overall goals of this surgical procedure are to create a clinically relevant model of chronic cardiac ischemia and to observe the effects of revascularization in this model using the current clinical therapy of coronary artery bypass graft surgery. This method can help answer key questions in the field of cardiothoracic surgery about how standard surgical treatments of blood flow restoration alter cardiac function and biology. The advantage of this technique is that it accurately mimics the gradual development of clinical atherosclerotic disease in a large animal model of chronic ischemia without infarction.
To create a model of hibernating myocardium, place a five-week-old, eight to 10 kilogram female Yorkshire pig onto it's right side and prep and drape the left side of the chest from the spine to the scapula, centering the third rib space in the sterile field. After IV Cefazolin administration, perform an intercostal nerve block at the second, third, and fourth ribs. To expose the heart, use monopolar electrocautery to make a lateral third spaced thoracotomy incision approximately 10 centimeters from the cranial aspect of the scapula to the axcilliary area, followed by an electrocautery incision to the skin and underlying musculature.
To prevent arrhythmia, deliver a two milligram per kilogram IV Lidocaine bolus and carefully insert a Finochietto rib retractor at the third intercostal space using gauze to retract the lung. Sharply incise the pericardium and use 2-0 polyglactin stay sutures to retract the pericardium to the side exposing the heart. Using a gauze-covered spatula retractor, retract the left atrial appendage and use Iris scissors to open the adventicia over the left anterior descending artery.
Bluntly dissect an approximately quarter centimeter portion of the artery, approximately one centimeter distal to the left anterior artery and the circumflex artery junction. Using a right angle clamp, encircle the left anterior descending artery and loosely place two 4-0 polyester sutures around the artery. Place a plastic c-shaped constrictor onto the left anterior descending artery proximal to the first diagonal, without occluding the vessel, and secure the constrictor with the two 4-0 polyester ties encircling the artery.
It is critical that large enough space is dissected around the left anterior descending artery to allow placement of the constrictor. Using a 2-0 polyglactin suture in a simple interrupted pattern, loosely close the pericardium and the intercostal muscle layer performing a breath-hold to remove the air from the chest as the intercostal muscle suture is tied. Carefully monitor the airway pressure manometer on the anesthesia machine to maintain the pressure in the 20 to 30 centimeters of water range, and release when the breath is complete.
Then use 2-0 and 3-0 absorbable sutures, respectively, to close the muscle and skin layers according to standard protocols and use skin adhesive over the incision for skin closure. At least eight weeks after constrictor placement surgery, place the chronically ischemic animal in the dorsal position and prepare the pickford surgery as just demonstrated. Using monopolar electrocautery, make an approximately three centimeter skin incision over the femoral artery to expose the artery for cannulation.
Connect the femoral cannula to a transducer to monitor the blood pressure during the surgery. Using electrocautery, make an incision from the manubrium to the xiphoid process to expose the sternum and divide the sternum with an oscillating saw. Use straight Mayo scissors to divide the posterior sternal plate and use a chest retractor to expose the thoracic cavity.
Remove any adhesions from the thoracotomy by monopolar electrocautery and have an assistant gently elevate the left sternal border. Using the same retractor, dissect the left internal mammary artery free from the chest wall and use hemoclips to control the arterial branches. When fully mobilized, heparinize the animal with 200 to 300 units per killogram of heparin for three minutes.
Next, over-sew the distal end of the artery and proximally place an occluder. Then use Iris scissors to create a three millimeter extension in the proximal end of the artery. Open and retract the pericardium and confirm that the length of the left internal mammary artery is adequate to reach the appropriate anastimotic sight on the left anterior descending artery.
Using a spring-form clip and cardiac stabilizer, open the adventicia to expose the left anterior descending artery and secure the opening with elastic tape. Place an appropriately-sized intralumenal device into the vessel and release the tape slightly to avoid ischemia. Use a running 7-0 polypropylene suture to anastimose the left internal mammary artery to left anterior descending artery and remove the intralumenal shunt.
After tying the suture, remove the occluder from the left internal mammary artery to establish the flow. Hemostasis is critical to the performance of the anastimosis. Have one assistant hold the left internal mammary artery and have another use an air blower device to keep the field dry during the anastimosis.
Once hemostatic, place a chest tube between the ribs on the left lateral chest and use suction to remove air from the chest cavity for 15 to 30 minutes. Place a suture around the chest tube and close the incision with number 5 polyester sutures in a figure 8 pattern to approximate the sternum. Close the muscle, subcutaneous, and the skin layers according to standard protocols.
When the wound is closed, remove the chest tube while performing a Valsalva maneuver to remove any residual air from the chest cavity and close the chest tube insertion site with one skin suture and an appropriate dressing. Then remove the femoral catheter and close the catheter incision with a 7-0 proline u-stitch closure. Following the initial hibernation surgery, stenosis greater than 70 percent, as well as the patent graft should be able to be visualized by cardiac MRI.
Eight weeks after the surgical application of the left anterior descending constrictor, the analysis of regional function by cardiac MRI reveals a reduced function under an increased workload in the left anterior descending artery restricted animals. Following a successful coronary artery bypass surgery, the animal may demonstrate incremental improvements in their regional cardiac function, both at rest and under anitropic stimulation, although these improvements do not restore function back to normal levels. A successful bypass surgery will also eliminate the mortality risk associated with hibernating myocardium.
Once mastered, the initial hibernation surgery can be completed in one and a half hours and the revascularization procedure can be completed in three hours if each technique is performed correctly. While attempting this procedure, it is important to remember to maintain a proper sterile technique and anesthetic depth, as well as to administer lidocaine before entering the pleural cavity to prevent arrythmia, and to administer heparin to prevent clotting. Following this procedure, this animal model of cardiac disease can be used to answer questions about disease etiology and to test novel therapies for chronic cardiac ischemia.
Generally, individuals new to this method will struggle because it is a highly technical vascular surgery. Surgical skills and loupes for magnification are important for success. After watching this video, you should have a good understanding of how to create a large animal model of chronic cardiac ischemia without infarction that is amenable to revascularization surgery.
Visual demonstration of this method is critical as the surgical techniques are complex due to the small size of the vessels. The dissection steps must be precisely completed to reduce the risk of bleeding and ventricular fibrillation.
