Our MRI-compatible minimally invasive closed chest swine model. It facilitates a more rapid translational study of ischemic heart disease. We've shown that a mother-and-child catheter can be used to precisely deploy coronary implants in a safe and quick manner, limiting adverse effects to the animal subjects.
Our method can be used to develop new diagnostic imaging techniques in ischemic heart disease. With some slight modifications, it can also be applied to other vascular disease states. Although it can be difficult to selectively cannulate the left main coronary artery in smaller pigs, using a mother-and-child catheter allows excellent quality angiograms to be obtained.
Our method allows us to induce a focal coronary lesion in the vessel of our choice and to conduct an MRI study on the same day. Visual demonstration of the technique will help reduce trial and error in future investigations, resulting in more reproducible results. The day before the procedure, use tweezers to dip coat printed implants in a 25%Heparin solution.
And allow the implants to dry for 24 hours. On the day of the procedure confirm an appropriate level of sedation in a 30 to 45 kilogram Yorkshire swine, and use the Seldinger technique to insert the arterial and venous sheaths into the bilateral femoral arteries and veins of the animal. Then flush all of the catheter ports continuously with Heparinized normal saline.
After vascular access has been obtained, administer 5, 000 to 10, 000 units of Heparin to maintain an activated clotting time of greater than 300 hundred seconds. For hemodynamic monitoring, use electrocardiography chest feeds for recording changes in the ST segment, T waves, and heart rate during the entire experimental period. Use a pressure transducer to record the continuous femoral arterial pressure throughout the procedure.
Attach a pulse oximeter to the animal's ear for continuous pulse oximetry recordings. Insert a deflated NC TREK over the wire coronary balloon through a mother-and-child catheter of the desired size such that the balloon tip extends beyond the tip of the catheter. Mount the 3D printed implant onto the deflated angioplasty balloon such that the implant is positioned between the markers of the balloon and close to the proximal marker.
Then use an Instaflator to inflate the balloon to two to three atmospheres to fix the implant onto the balloon and verify that the implant is positioned closer to the proximal half of the balloon so it'll be closest to the mother-and-child catheter when ready for removal. To induce a coronary angiography with a fluoroscopic C-arm in the antero posterior projection, attach a control valve to a left or right coronary guide catheter. Introduce the guide catheter over a J tipped wire through the right femoral artery sheath.
And under fluoroscopic guidance advance the catheter to the aortic root. Selectively engage the catheter into the left main coronary artery, and inject five milliliters of iodinated contrast under fluoroscopy to visualize the left coronary system. Position the guide catheter toward the left main coronary artery for the second angiogram.
Once engaged within or position near the left main coronary artery, advance a 0.014 inch 300 centimeter coronary wire into the left main coronary artery and further advance the wire to the distal left anterior descending artery. Insert the previously assembled mother-and-child catheter with the inflated coronary angioplasty balloon and implant over the coronary wire and advance the assembly to the desired location along the coronary vessel. Inject five milliliters of iodinated contrast to visualize a discreet narrowing at the desired location where the coronary implant should be deployed.
Once the implant is in position, advance the mother-and-child catheter to the proximal marker of the inflated balloon. The geometric constraints of the delivery system allow the stenosis to be positioned within the proximal to mid portion of the pig coronary artery. Deflate the balloon and retract it through the mother-and-child catheter to shear the implant off the balloon as it is retracted, fixing the position of the implant within the designated segment of the vessel.
Then perform final angiograms to document the location of the new artificial stenosis within the vessel and two orthogonal views as possible to acquire visual estimation of the stenosis severity. After harvest, dissect the ex-vivo heart to expose the coronary vessels. Note the location of the implant in relation to the branches it was positioned next to to retrieve the implants and inspect the vessel for gross injury.
Then photograph the heart tissue for gross pathology and stain with TTC to exclude myocardial infarction. In these stress cardiac profusion magnetic resonance images of a coronary implant deployed in the proximal to mid left anterior descending artery, the implanted vessel can be observed at rest and at peak adenosine vasodilator stress. Note the inducible perfusion defects in the segments subtended by the left anterior descending artery.
Remember to ensure that the mother-and-child catheter is flush against the implant in a stable position prior to deflation of the coronary balloon to allow for shearing of the balloon upon withdrawal. We can now deploy an implant and conduct an entire MR imaging study start to finish in a single day, drastically cutting down on the timing and logistical challenges for these experiments.
