It is important to evaluate new heart preservation strategies using clinically relevant large-animal model for a reliable clinical translation. The porcine heart model for research in cardiac surgery is a very useful one because human and porcine hearts share lots of similarities in terms of anatomy, physiology, even size, so it's an almost ideal platform for research. After opening the pericardium of an anesthetized donor pig, have an assistant carefully retract the right ventricular outflow tract inferiorly and the pulmonary artery to the left and carefully retract the aorta to the right to avoid direct lesions to the pulmonary artery.
Use the cautery to dissect the aortal pulmonary space and clear the anterior aspect of the ascending aorta from the connective tissue. After carefully retracting the right ventricular outflow tract use a 4.0 PROLENE suture to place a purse string stitch on the proximal ascending aorta adventitia and secure the suture with a tourniquet. Insert the cardioplegia delivery cannula into the ascending aorta within the purse string suture and tighten the tourniquet to secure the cannula.
Next open the left inferior pulmonary vein and the superior and inferior vena cavae to ensure adequate cardiac venting and place the aortic cross-clamp on the distal ascending aorta. Initiate cardioplegia infusion targeting an aortic root pressure of 80 to 100 millimeters of mercury. Apply a 0.9%sodium chloride ice slush to the thoracic cavity and over the organ.
When the cardioplegia infusion is finished, proceed with the cardiectomy in a traditional manner, sectioning the aorta after the innominate artery and the pulmonary artery and at the bifurcation to ensure a sufficient length for the implant. To initiate a cardiopulmonary bypass in the recipient, first use Metzenbaum and right angle forceps to dissect between the superior vena cava and the innominate artery and the inferior vena cava and the pericardium of the anesthetized recipient animal. Individually encircle the superior and inferior vena cavae with a 0-silk tie and secure each tape with a tourniquet.
Use a 4-0 PROLENE suture to place two concentric purse string sutures on the distal ascending aorta adventitia and place purse string sutures on the inferior and superior vena cavae at the level of the pericardial reflection. Secure each suture with a tourniquet and use the Seldinger technique to insert a 17-21 French arterial cannula into the aorta. Use a 3/8-3/8 connector to connect the cannula to the arterial line of the bypass circuit.
Make a five-millimeter incision at the center of the purse string sutures placed on the vena cavae and dilate the incision with a small angled instrument. Using a 24-28 French right-angled, single-stage venous cannula, cannulate the superior and inferior vena cavae, directing the angle superiorly in the superior vena cava and inferiorly into the inferior vena cava, away from the heart. Tighten the tourniquet holding the purse string suture to secure the cannula, and use a 3/8-3/8 1/2-Y connector to connect the cannulas to the venous line of the bypass circuit.
Then initiate the cardiopulmonary bypass. After cardiopulmonary bypass initiation, use a sharp dissection instrument and a right angle to encircle the left hemiazygos vein and ligate the vessel distally with an O-silk tie. Cross-clamp the recipient aorta proximally to the arterial cannula and snare both vena cavae with the previously placed O-silk ties.
Compare the left atrial cuff sizes of the donor and recipient and modify each as necessary. Deliver the first cardioplegia dose to the donor heart using the previously placed cardioplegia cannula. Next use the standard biatrial anastomotic technique and an SH needle to place one 4-0 PROLENE suture at the junction between the left atrium and the right inferior margin of the inferior vena cava.
Place another suture at 180 degrees from the first suture to connect the donor and recipient cuffs, then complete the posterior and anterior wall anastomoses from the superior suture to the inferior suture. For the right atrium, open the donor right atrium from the appendage towards the inferior vena cava, creating a donor cuff that matches the recipient cuff size, then, starting at the junction between the inferior vena cava and the right atrium, complete the interior wall anastomosis and then the lateral wall. For the pulmonary artery, trim the edges of both the recipient and donor pulmonary arteries to create matching sizes.
Use a BB needle to place a 5-0 PROLENE suture at the left lateral wall, uniting the donor and recipient vessels, and another at the right lateral edge. Then complete the inferior wall anastomosis and the anterior wall anastomosis. For the aorta, trim the edges as just demonstrated and place a suture on the left lateral wall connecting the donor and recipient vessels.
Then complete the inferior wall and the anterior wall anastomosis before initiating a 60-minute reperfusion on the cardiopulmonary bypass. For a functional assessment of the graft, place a 0-silk tie around the inferior vena cava and insert a pressure-volume conductance catheter into the left ventricle through a small apical ventriculotomy to permit continuous measurements of the left ventricular pressure-volume relations. Here representative results from pressure-volume relationships and echocardiographic parameters taken at baseline, and at three hours post-transplantation in a set of five experiments are shown.
During steady-state assessments, volume-dependent parameters are recorded such as the maximum and minimum rate of developed pressure. Volume-independent parameters are obtained by intermittent occlusion of the inferior vena cava during which the volume of the left ventricle progressively decreases and the end-systolic and end-diastolic pressure-volume relationships are recorded. The pre-load recruitable stroke work data can be used to determine the relationship between the stroke work and the corresponding end-diastolic volume.
Various other metabolic parameters can also be measured with this model. This procedure requires at least one trained surgeon and approximately five practice experiments to optimize the research protocol for each research group. The porcine heart is fragile, friable, and especially sensitive to manipulation and ischemia, thus being prone to tears.
It is important to revise all anastomoses to ensure minimal to no bleeding. This protocol can help in the development of new myocardial preservation strategies to decrease ischemia-perfusion injury and to prevent primary graft failure.
