Surgical Porcine Model of Chronic Myocardial Ischemia Treated by Exosome-laden Collagen Patch and Off-pump Coronary Artery Bypass Graft

The overall goal of this surgical procedure is to create a surgical model of coronary artery revascularization using LIMA-to-LAD bypass and the use of exosome-laden collagen patch as an adjunct to demonstrate physiological improvement in cardiac function. Our in vivo model is a single vessel model that does not include any comorbidities, which is not representative of the typical clinical situation for patients undergoing treatment for multivessel disease. However, despite this limitation, our model has consistently produced reliable results and has maintained low mortality rates.

We developed a clinically relevant adjuvant therapy to be used during CABG and aim to understand the cellular mechanisms driving the myocardial functional improvement in chronic myocardial ischemia. Complete recovery of ischemic tissue appears to hinge on restoration of mitochondrial capabilities and reduced inflammation representing a novel area of study. To begin, position the anesthetized and intubated animal on its back and cover it with sterile towels.

Use monopolar electrocautery to make a 20-centimeter incision extending from the sternal notch approximately down to the xiphoid process distally and to incise layers of muscles, subcutaneous fat and connective tissue down to the sternum. Then carry out a medium sternotomy, employing an oscillating saw. For efficient visualization of the mediastinum, use a specialized chest retractor.

Dissect adhesions using monopolar electrocautery or Metzenbaum scissors. Then expose LIMA by dissecting the parasternal muscle and fat. Next, start the dissection of the LIMA by elevating the left sternal border to ensure optimal visualization.

Apply gentle traction to the adventitia and expose the arterial and venous branches of the LIMA. Employ blunt dissection using electrocautery tip to carefully separate it from the chest wall. Use Hem-o-lok clips on the branches and cauterize the chest wall side of these branches.

Then, clip the distal end of the LIMA just before the point of bifurcation and divide the conduit. Secure the distal end with a freely tied 2.0 silk suture. After preparing the proximal end for grafting, evaluate the flow quality manually by allowing the graft to bleed briefly.

Now, clamp the distal end of the LIMA conduit with an atraumatic bulldog clamp to prevent bleeding. Stabilize the left anterior descending or LAD artery using silicone retraction tape and a tissue stabilizer that's secured to the sternal retractor. Perform an arteriotomy in the LAD artery distal to the stenosis using an 11 blade, and extend the incision with iris scissors.

Position an appropriately sized coronary shunt in the LAD artery. Conduct the LIMA to LAD anastomosis using a 7-0 non-absorbable running suture in an off pump bypass technique. Take a three millimeter exosome suspension and use a five milliliter syringe equipped with an 18 gauge needle to mix it.

Then, gradually pipette 1.5 milliliters of this suspension onto two absorbable collagen sponges placed in a medium sized Petri dish. To target the hibernating region of the heart, place the exosome sponge upside down on the epicardium of the anterior septal region in the distribution of the LAD artery. Carefully arrange two sponges to fully cover the hibernating region.

Use a polyglactin mesh on each collagen sponge to ensure proper coverage and sew the mesh onto the epicardium with fine 7-0 interrupted sutures. Make a separate stab incision near the inferior aspect of the sternotomy incision and place the chest tube carefully on the anterior aspect of the heart. Approximate the sternum using non-absorbable sutures, employing a figure eight pattern.

Close layers of muscle and skin using 2.0 and 3.0 absorbable sutures respectively following the standard procedure. After evacuating the chest cavity with a chest tube, seal the wound using a purse-string suture. Once the wound is closed, remove the chest tube.

At rest, the peak filling rate over end-diastolic volume is compared among four animal groups. In low dose dobutamine infusion, the group with hibernating myocardium had a decrease in peak filling rate. The coronary artery bypass graft surgery group showed improvement while the coronary artery bypass graft plus mesenchymal stem cell group saw a significant increase.

MRI analysis revealed that coronary artery bypass graft plus mesenchymal stem cell group does not alter regional systolic function at rest. However, under stress, this group showed significant improvement in regional systolic function compared to coronary artery bypass graft.