NOTE: Two female Yucatan pigs are selected, with one designated to be the cardiac graft donor and the other the recipient. Pigs aged 6-8 months, weighing approximately 30 kg, and having compatible blood types are recommended. The overview of the protocol is demonstrated in Figure 1. Housing and the treatment procedures for the pigs are performed in accordance with the guidelines of the Animal Care and Use Committee of Duke University Medical Center.
1. Preparation of the ex vivo perfusion device
- Prepare the ex vivo perfusion device and a cell saver device for use per the manufacturer's guidelines.
- Have a pacing box and defibrillator available and set them up.
- Have a point-of-care (POC) testing device available to check a complete blood count (CBC), basic metabolic panel (BMP), and arterial blood gas (ABG).
- Add the following medications to the perfusion priming solution provided by the manufacturer, if not already present in the manufacturer's perfusion solution: 100 mL of 25% albumin, 10 mL of 200 mg/100 mL ciprofloxacin, 1 g of cefazolin sodium, two 5 mL vials of multi-vitamin injection, 250 mg of methylprednisolone, 10,000 IU of heparin, and 50 IU of insulin.
- Perform POC testing of the ex vivo device priming solution to ensure that the electrolyte levels are within the normal physiologic range. If not, administer calcium gluconate, dextrose, and/or sodium bicarbonate accordingly to supplement any subtherapeutic electrolyte or glucose levels.
- To add the priming solution with the added medications, spike the solution and de-air the line delivering the solution to the ex vivo perfusion device.
NOTE: Skip to section 6 for instructions on priming the ex vivo perfusion device.
2. Initiation of anesthesia and IV access in the donor pig
- After fasting the pig for 8-12 h, premedicate it with ketamine (5-33 mg/kg, intramuscular) and midazolam (0.2-0.5 mg/kg, intramuscular) and administer isoflurane (1-4%) using a face mask.
- Place the pig in a supine position and intubate with an endotracheal tube (ETT) (5.5-6.5 mm internal diameter) to protect the airway. Secure the ETT by tying it to the pig's snout. Position the extremities using heavy ties attached to the table.
- Apply vet ointment on the eyes to prevent dryness while under anesthesia.
- Place an intravenous (IV) catheter (20-22 G) in an ear vein.
- Initiate maintenance IV fluids (Lactated Ringer's solution at 10 mL·(kg·h)-1).
- Administer intramuscular (IM) Buprenorphine 0.005-0.01 mg/kg for analgesia.
3. Vital signs and central line settings
- Start mechanical ventilation at a tidal volume of 10 mL·(kg·min)-1 and a rate of 10-15 breaths per minute with isoflurane (1-3%) maintained throughout the procedure such that reflexes are absent and the heart rate (>60 bpm, <100 bpm) and blood pressure (systolic blood pressure >90 mmHg, <130 mmHg) remain within the physiologic range.
NOTE: The addition of a paralytic is optional.
- Continuously monitor oxygen saturation and heart rates throughout the surgery.
4. Median sternotomy of the donor pig
- Palpate the sternum from the manubrium to the xiphoid. Mark the midline using a sterile surgical marker. Shave any hair from the site with a hair clipper and sterilize the area using 4% chlorhexidine for a total of 3 rounds of sterilization. Apply a sterile surgical drape around the immediate surgical site.
NOTE: Surgeons must wash hands and arms with an alcohol- or iodine-based wash and don sterile gowns and gloves.
- Use a no. 10 blade to make an incision from the manubrium down to the xiphoid, measuring 20-30 cm, depending on the size of the pig.
- Use electrocautery to divide the pectoralis major down from the sternum to the xiphoid, being careful to do this along the midline of the sternum. Once down to the sternum, score the midline and begin the sternotomy from the xiphoid by dividing it with heavy scissors.
- Extend the sternotomy cephalad with heavy scissors. After each cut, bluntly separate the heart from the sternum using finger sweeps. In this manner, complete the sternotomy through the manubrium.
- After completing the sternotomy, achieve hemostasis by applying electrocautery to the cut bone edges.
- Place a sternal retractor and open it to optimize the exposure of the surgical field. Identify and remove the thymus with electrocautery. Enter the pericardium longitudinally from the diaphragm to the aorta. Create a pericardial cradle using 5-6 size: 2-0, silk sutures.
5. Cardiac arrest and cardiectomy of the donor pig
- Fully divide the tissue between the aorta and pulmonary artery (PA) and visualize the location of the aortic arch and the brachiocephalic trunk to facilitate proper placement of the aortic cross-clamp.
NOTE: The ascending aorta is much shorter in the pig versus human.
- Circumferentially free the superior vena cava (SVC) using scissors and blunt dissection. Pass two, size: 0, silk ties around the SVC.
- Circumferentially free the inferior vena cava (IVC) using scissors and blunt dissection. Similarly, pass two 0 silk ties around the IVC.
- Apply a U-stitch, size: 4-0, polypropylene suture to the ascending aorta.
- Apply a purse-string, size: 4-0, polypropylene suture to the right atrium (RA).
- Administer a bolus of heparin IV using an initial dose of 300 U/kg.
- Insert a pediatric 4-Fr aortic root cannula, secured by the previously placed U-stitch. De-air the cannula and secure it in place with a Rummel tourniquet.
- Connect the aortic root cannula to the cardioplegia tubing after the tubing has been flushed with del Nido cardioplegia. Flush with the necessary amount to remove any air bubbles within the tubing.
NOTE: Communication with the perfusion team is critical at this point to correctly execute the cardiac arrest.
- Ensure the perfusionist(s) have installed the cell saver disposables in a sterile fashion, primed the device as recommended by the manufacturer (see section 6), and are ready to process the collected blood.
- Confirm that the cell saver cardiotomy (plastic container attached to the cell saver device where blood is stored after washing) is ready with 10,000 U of heparin and that the cardiotomy is connected to suction, not to exceed -150 mmHg of pressure.
NOTE: This is to avoid hemolysis of red blood cells.
- Create a right atriotomy within the previously placed purse-string, insert a 24 Fr venous cannula into the RA, and secure with a Rummel tourniquet.
- Connect the venous cannula to a sterile suction line connected to the cell saver cardiotomy and collect approximately 1-1.3 L of blood. Then, apply the aortic cross-clamp, carefully ensuring that the clamp completely occludes the ascending aorta. Administer 500 mL of Del Nido cardioplegia into the root at a pressure of 100-150 mmHg using a pressure bag.
NOTE: The heart will blanch and arrest.
- Place sterile ice slush on the heart.
- Once the cardioplegia is delivered, remove the aortic root cannula and the RA venous cannula and tie the purse-string sutures down.
- Divide the following: the IVC, the SVC just proximal to the azygos vein, the aorta at the level of the arch just distal to the Innominate artery, the main PA at the bifurcation, and the left azygous vein as it enters the coronary sinus.
NOTE: Pigs have a left azygous vein that drains into the coronary sinus.
- Identify the pulmonary veins and ligate them with size: 2-0, silk ties or large-sized clips. Leave one pulmonary vein open for the insertion of the LV vent.
- Remove the heart from the chest and place it in a container with sterile ice slush.
- Move the heart to the backtable to prepare the graft for placement on the ex vivo perfusion device.
6. Washing the donor blood and priming the ex vivo perfusion device
NOTE: This step is necessary to remove any components from the donor serum that might neutralize the delivery of the therapeutic when it is introduced to the perfusate. Perform this step during the explantation of the donor heart to minimize the allograft ischemic time.
- Complete a cell saver prime and wash cycle.
- Install the disposable components into the device per the manufacturer's instructions.
- Prime the cell saver device by spiking Plasmalyte A and selecting the prime function on the device. Add as much Plasmalyte A as the volume of blood collected from the donor pig in a 1:1 fashion.
NOTE: Once the device completes the priming cycle, it is ready for the addition of blood. See sections 5.9-5.11 for how to add the blood from the donor pig.
- Once the blood is in the device, select the wash cycle on the cell saver device.
NOTE: During this process, the blood is centrifuged while the Plasmalyte A is introduced to wash the blood. This step concentrates and washes the blood.
- Transfer the washed blood into a blood collection bag for transfer to the ex vivo device.
- Add the washed blood to the ex vivo perfusion device per the manufacturer's guidelines.
- Prepare an epinephrine solution by injecting 0.25 mg epinephrine and 30 IU of insulin into 500 mL of 5% dextrose in water during priming of the ex vivo machine. Spike the solution and de-air the line delivering the solution to the ex vivo device.
- Add 10,000 U of heparin to the ex vivo perfusion device.
- Add 5% albumin to reconstitute the blood.
NOTE: The volume of 5% albumin added to the device equals the amount of plasma removed by the cell saver device. This is done to help achieve a physiologic oncotic pressure and hematocrit.
- Turn the pump on to flow at 1-1.5 L/min to prime the circuit with the clear prime, drugs, and blood administered into the reservoir. After turning the pump flow on and circulating the prime through the perfusion module, ensure that the lines of the circuit are air-free.
NOTE: The final maintenance solution volume is 1000 mL in addition to the volume of washed blood.
- Obtain a baseline perfusate POC chemistry and lactate using the POC testing device. Replenish electrolytes as needed.
- Add enough dextrose to maintain a minimum glucose level of 100 mg/dL.
- Add enough sodium bicarbonate to maintain a minimum pH goal of 7.4.
NOTE: Importantly, added sodium bicarbonate cannot be removed from the perfusate. Excess sodium levels will contribute to the heart becoming edematous and must be avoided. Caution needs to be taken when treating the base deficit, as the heart will begin to correct the base deficit upon reanimation.
- Add enough calcium gluconate to maintain a minimum ionized calcium level of 0.8 mmol/L.
- Set the temperature at 37 °C.
- Set the gas flow rate to 150 mL/min and adjust as needed to achieve a physiologic pCO2 level.
- Set the mean arterial pressure (MAP) target to 60-70 mmHg.
- Turn down the pump flow to 0.6 L/min.
7. Backtable preparation of the donor heart and reanimating the heart
- Oversew the SVC. Place four pledgeted, size: 4-0, polypropylene sutures in a simple horizontal mattress fashion around the inside of the distal aorta, 5 mm below the cut edge and tie them down.
- While holding up the 4, size: 4-0, pledgeted aortic sutures, insert the aortic connector into the aorta, and tie an umbilical tape around the aorta to secure the connector.
- Place a size: 4-0, polypropylene purse-string around the distal cut edge of the main PA. Insert the PA cannula and tie down the ends of the purse-string to secure the cannula.
- Take the prepared graft from the backtable to the ex vivo perfusion device and connect the aortic connector to the device. Be sure to de-air the aorta/aortic connector before securing the heart to the device.
- Start the perfusion clock, maintain the pump flow around 0.6 L/min, and decrease the temperature set point to 34 °C.
- Start the epinephrine and maintenance drips per the manufacturer's recommendations.
- Connect the PA cannula to the PA connector on the device and secure it with a tie.
- Place the left ventricle (LV) vent drain through the untied pulmonary vein into the left atrium and across the mitral valve into the LV. Secure the vent in place with a single stitch to properly anchor it.
- Place two cardiac pacing leads onto the LV free wall.
- Check lactate, ABG, CBC, and BMP every hour. Administer potassium, 50% dextrose, and calcium as needed to maintain normal physiologic levels.
NOTE: More frequent lactate sampling may be appropriate during early stabilization to establish adequate perfusion based on lactate.
- If pacing is required, set the ventricular pace at 80 beats per minute at 10 mA (atrial pacing is typically not utilized).
- If defibrillation is required, start at 10 J after the temperature on the device has reached 34 °C. Do not exceed 50 J.
NOTE: Goal total average flow is 600 mL/min, and average coronary flow is 400 mL/min.
8. Administering the therapeutic
- Draw up the therapeutic into a syringe in a sterile fashion.
- De-air the cardioplegia port by using a sterile 3 mL syringe to draw blood through the port. Administer the therapeutic into the cardioplegia port (or equivalent) such that the therapeutic is introduced directly into the aortic root.
- Flush the port with the volume of collected blood drawn in step 8.2 when de-airing the port; be careful not to flush any air with it.
NOTE: This is to ensure the therapeutic is administered into the heart's aortic root.
NOTE: This section has been previously described in detail in Bishawi et al. to introduce viral vectors for luciferase expression15.
- Perfuse the graft on the device for 2 h after introducing the therapeutic.
9. Preparation of the recipient and laparotomy with vascular exposure
- Once the cardiac allograft is secured to the device and the therapeutic is introduced into the circuit, begin the induction of anesthesia and preoperative preparation as described in section 2 for the recipient pig.
- Initiate infusion of the immunosuppression medications: cyclosporine 50 mg/kg total as a slow drip infusion throughout the procedure and methylprednisolone 1 g IV bolus.
- Administer antibiotics: enrofloxacin IM (5 mg/kg) and cefazolin 1 g IV bolus.
- Insert a Foley catheter into the bladder.
NOTE: Decompressing the bladder aids with obtaining an optimal exposure of the infrarenal aorta and IVC.
- Mark the abdominal midline from mid-abdomen to the pubis using a sterile surgical marker. Shave any hair from the site with a hair clipper and sterilize the area using 4% chlorhexidine for a total of 3 rounds of sterilization. Apply a sterile surgical drape around the immediate surgical site.
NOTE: Surgeons must wash hands and arms with an alcohol- or iodine-based wash and don sterile gowns and gloves.
- Use a 10 blade to incise the skin (20-30 cm incision) and switch to electrocautery to dissect down to the fascia.
- Use two Kocher clamps to lift the fascia and peritoneum and carefully make a small incision (1 cm) into the peritoneal cavity using Metzenbaum scissors.
- Extend the peritoneal opening for the full length of the incision using electrocautery, placing a finger underneath to protect the underlying viscera. Place a Balfour retractor to optimize exposure. Retract the small bowel cranially and with wet towels.
- Open the retroperitoneal space inferior to the kidneys with care directed towards identifying the ureters and avoiding injury.
- Carry the dissection down to the abdominal aorta and IVC. Ligate the lymphatics with medium and large clips.
- Dissect the vessels circumferentially and expose a large enough segment to fit a large Satinsky clamp around each vessel. Take care to avoid disruption of lumbar arterial branches, which come off of the posterior part of the aorta. Place two vessel loops around the aorta and IVC at the proximal and distal ends of the exposure.
10. Final arrest and removing the heart from the ex vivo perfusion device
- At the end of the 2 h of ex vivo perfusion, connect the heater-cooler machine to the ex vivo device. Set the heater cooler temperature to 34 °C.
- In a sterile and air-free fashion, connect the de-aired cardioplegia delivery line to the ex vivo device at the aortic access port.
- Turn the temperature set point on the ex vivo device to off.
- Reduce the heater-cooler temperature to 24 °C and decrease pump flow to maintain MAP between 60 and 70 mmHg (typically a change in pump flow from 1 L/min down to 0.9 L/min).
- Once the temperature reading on the ex vivo perfusion device reaches 24-26 °C, reduce the heater-cooler temperature further to 14 °C and decrease the pump flow further by 100 mL/min.
- Once the temperature reaches 14-16 °C, detach the PA cannula from the PA port, start the delivery of antegrade del Nido (500 mL), close the AO line valve, stop the pump, and quickly clamp the AO vent line.
NOTE: Cardioplegia delivery pressure needs to be titrated to maintain a mean delivery pressure of 45-65 mmHg as displayed on the ex vivo device monitor.
- Remove the heart from the ex vivo perfusion device by disconnecting the PA cannula and the aortic connector and cutting the pacing wires.
- Place the heart in a bucket filled with sterile ice slush.
- On the backtable, oversew the pulmonary vein/left atriotomy where the LV vent had been inserted. Trim (1 or 2 mm) of the distal aspect of the aorta and PA where attachment to the cannulas may have crushed the tissue.
NOTE: The heart is now ready for intraabdominal, heterotopic implantation.
11. Heterotopic implantation of the cardiac graft
- Before placing the Satinsky clamps, administer 300 U/kg of IV heparin to the recipient pig.
- Place a Satinsky clamp on the IVC and create a longitudinal venotomy measuring ~1.5 cm using an 11-blade and Pott's scissors.
- Anastomose the graft PA to the recipient's infra-renal IVC in an end-to-side fashion using a running, size: 4-0, polypropylene suture. Perform the inner part of the anastomosis first and reinforce as necessary with interrupted sutures before completing the outer part of the anastomosis.
NOTE: The PA to IVC anastomosis is performed first, and the aorta-to-aorta anastomosis is done last to reduce the duration of aortic occlusion.
- Place a Satinsky clamp on the aorta and create a longitudinal aortotomy measuring ~1.5 cm using an 11-blade and Pott's scissors.
NOTE: Obtain an ABG prior to clamp placement. Recheck it immediately after clamp release and again 15-30 min later to assess any changes in hyperkalemia, hyperlactatemia, or acidemia indicative of ischemic injury in the recipient.
- Anastomose the graft aorta to the recipient's infra-renal aorta in an end-to-side fashion using a running, size: 4-0, polypropylene suture. Perform the inner part of the anastomosis first and reinforce as necessary with interrupted sutures before completing the outer part of the anastomosis.
- Remove the Satinsky clamps to reperfuse the heart; first, remove the IVC clamp followed by the aortic clamp.
- Place an 18 G angiocath into the LV apex of the graft to de-air. When done, remove the angiocath and close the site with a pledgeted suture.
- Carefully check the anastomoses for any bleeding.
- Carefully place the heart into the right retroperitoneal space, such that there is no tension on the anastomoses and no kinking of the vessels. Replace the small bowel.
12. Closure of the laparotomy
- Close the fascia with looped, size: 0, Maxon suture in a running fashion starting from both ends of the incision and tying in the middle. Take care to avoid any injury to the bowel.
- Close the deep dermal layer with size: 2-0, Vicryl in a running fashion and the skin with size: 4-0, Monocryl in a running fashion.
- Clean the skin incision and apply skin glue.
13. Postsurgical treatment and euthanasia
- After completion of the surgery, turn off the isoflurane flow and monitor the pig for return of muscular tone and neuromuscular reflexes (corneal reflex, withdrawal to painful stimuli, swallowing).
- After confirming the restoration of these functions, turn off mechanical ventilation and observe for spontaneous breathing. If there is spontaneous breathing, remove the endotracheal tube; if there is not, reconnect the endotracheal tube to mechanical ventilation.
- Transfer the pig off the operating table to an isolated enclosure where its vital signs (rectal temperature, blood pressure, heart rate) can be closely monitored. Use a heating lamp to warm the pig as necessary. Provide an IV fluid bolus of 250 mL of Lactated Ringer's solution in the setting of hypotension (systolic blood pressure < 100mmHg). Continue to monitor the pig until it can maintain sternal recumbency and vital signs are fully normalized.
NOTE: The animal is not left unattended until it has regained sufficient consciousness. Additionally, the animal is not returned to the company of other animals until fully recovered.
- For pain management, administer a one-time dose of buprenorphine (sustained release) subcutaneous injection 0.12 mg/kg for 72 h of analgesia.
- At the end of the experimental period, euthanize the pig for explantation of the native (thoracic) heart and the allograft (abdominal) heart.
- Prepare the pig as described in sections 2 and 3 for the procedure. Prepare two bags of del Nido and two cardioplegia lines for arresting each heart.
- Expose the thoracic heart as described in section 4. Once complete, proceed to perform a laparotomy as described in section 9.
- Once the aorto-aortic and PA-IVC anastomoses are exposed, place a Satinsky clamp on the recipient aorta and another on the recipient IVC to isolate the allograft from the systemic circulation.
- Insert a pediatric 4-Fr aortic root cannula into the aortic root of the allograft and connect a cardioplegia line to the catheter. Administer 500 mL of del Nido cardioplegia into the root at a pressure of 100-150 mmHg using a pressure bag. After the infusion is started, use Metzenbaum scissors to make a 2 cm incision at the level of the PA-IVC anastomosis to vent the allograft.
- Once the allograft is arrested, proceed to explant the allograft by using Metzenbaum scissors to excise at the level of the aorto-aortic anastomosis and the remainder of the PA-IVC anastomosis. Do not remove any of the Satinsky clamps.
- Proceed with the removal of the thoracic heart as described in section 5.
NOTE: The only significant difference is that the pulmonary veins do not need to be carefully ligated and can instead be grossly dissected using Metzenbaum scissors when performing the cardiectomy.