The overall goal of this procedure is to perform a complete heart replacement in a large animal model, using two centrifugal implanted pumps. This method can help answer key questions in the surgical heart failure field, regarding the optimal speed settings for intracorporeal, biventricular support using two centrifugal flow ventricular assist devices. This technique allows for real-time systemic and pulmonary pressure assessments in situations where the total artificial heart is not an option.
After performing a sternotomy, score the bleeding muscle edges with an electric cautery tool, and apply bone wax to the sternum to help with any residual bleeding. Use the cautery tool to remove the thymus, and enter the pericardium in a longitudinal fashion, reflecting from the diaphragm to the aorta. Using 520 silk sutures, bring all of the corners of the pericardium directly anterior to the skin, to create a pericardial cradle for supporting the heart.
Dissect the connective tissue to create a 3-inch long window between the aorta and the pulmonary artery, then apply a purse string 3-0 polypropylene suture to the ascending aorta, proximal to the bifurcation. Use blunt dissection to circumferentially free the superior vena cava, or SVC, and place a second purse string using a 3-0 polypropylene suture. Administer an initial dose of 300 units of heparin per kilogram, to achieve an activated clotting time greater than 400 seconds, and to establish systemic herparinization.
Then use a number 11 blade to incise the aorta, and insert an 18 French arterial cannula. After de-airing the cannula, attach it to the arterial line of the cardio-pulmonary bypass, or CPB. Place a 28 French right-angle cannula in the SVC, and initiate the CPB.
Cannulate the inferior vena cava, or IVC, as just demonstrated for the SVC. Then, use a Y-connector to splice together the SVC and IVC drains into one main circuit, and loop both the SVC and IVC with umbilical tape to allow complete blood isolation from the heart. While on full cardio-pulmonary support, use the tape to snare down the SVC and IVC, and apply an aortic cross-clamp proximal to the aortic cannulation site.
When the clamp is in place, circumferentially excise the ventricular tissue one to two centimeters distal to the right and left atrial ventricular grooves, leaving the rim of the ventricular muscle with the mitral and tricuspid annuli to provide further support for the implantation of the sewing rings. Transect the sub-valvular apparati for the mitral and tricuspid valves as they are encountered, and excise the right ventricular outflow tract, or RVOT muscle, and the RVOT itself, including the pulmonary valve. Next, open the left ventricular outflow tract, or LVOT, taking care to preserve the posterior aspect of the aortic valve, as part of the aortal mitral curtain.
Then, resect the residual intraventricular septum, leaving at least a one centimeter room of muscle at the mitral and tricuspid annuli, and ligate the orifice of the coronary sinus with 5-0 polypropylene sutures. For implantation of the centrifugal flow pumps, or CFP, first use pledgeted interrupted 2-0 braided sutures to secure a sewing ring to the ventricular tissue and mitral valve annulus, exiting the sutures on the epicardial surface of the ventricular muscle rim, and bringing the sutures through the sewing ring. The sutures must be placed in a manner to avoid ventricular tissue bunching when the ring is being tied down.
Using a similar approach, attach the sewing ring to the right ventricular muscle rim and tricuspid annulus, and attach the CFPs to the sewing rings using the standard locking mechanism to secure the pumps. Adjust the outflow graft length according to the orientation of choice, and cut the outflow graft to the appropriate length. Bevel the cut of the graft if the diameter is less than that of the aorta or pulmonary artery.
Using running 4-0 polypropylene sutures, anastomose the outflow grafts to the aorta for the left CFP, and to the main pulmonary artery for the right CFP, in an end-to-end fashion, releasing the tape on the SVC and IVC drainage cannulas prior to completing the anastomosies, to fill the pumps and grafts. Start the clearing process, allowing blood to fill the right and left pumps, and place an 18-gauge needle into each of the outflow grafts for further de-airing. Use the ventilator to provide large volume breaths to allow any air trapped in the pulmonary veins to be removed.
When the de-airing is complete, remove the needle and use pledgeted 5-0 polypropylene sutures to repair the site. Now, start the pumps at 3, 000 RPM, and remove the aortic cross-clamp. Gradually increase the pump speeds while weaning and terminating the CPB, to allow the circulation to be supported entirely by the right and left side pumps.
Introduce the pressure catheters directly into the left atrium, and use a purse string 5-0 polypropylene suture to secure the catheters in place. Transduce the pressure signals to the software under the labels pulmonary artery and pulmonary vein. To establish the biventricular assist device flow, slowly increase first the left CFP speed, followed by a slow increase of the right CFP speed, while gradually decreasing the CPB flow.
Pay careful attention to the hemodynamics, including the systemic blood pressure and central venous pressure. Increase the left and right CFP speeds as necessary to achieve a flow of approximately four liters per minute on each side, to achieve normal pulmonary artery and vein pressures. Once hemodynamic stability is achieved, remove the SVC and IVC cannulas, and tie down the purse string sutures.
In this image, improper ring attachment resulted in bunching of the ventricle tissue, which may create a problem with the pump attachment. Here, the pumps are positioned so that the outflow grafts are short, and exit directly into the connected arteries. In this alternative orientation, the outflow grafts are positioned so that both the right and the left CFPs are able to rotate circumferentially prior to being anastomosed to the pulmonary artery and aorta, respectively.
Once mastered, this technique can be performed in about three hours, if done properly.
