An Ex Vivo Porcine Model for Hydrodynamic Testing of Experimental Aortic Valve Procedures and Novel Medical Devices

Limited options exist for testing new cardiac procedures and investigative medical devices before use in a large-animal model. Our protocol provides the opportunity to fine-tune such procedures and devices in a biologically and anatomically relevant context prior to embarking on large-animal studies. Other techniques for mounting an aortic valve on a pulse duplicator require inserting or fixing a rigid structure to the aortic valve annulus, thus distorting the valve's hydrodynamic properties.

Our protocol offers an innovative way to cannulate the LVOT so that all measured hydrodynamic properties are valid. This method is designed to assess the viability of leaflet substitution materials for use as a valve repair patch or prosthesis. It is a pivotal tool for our future research, in which we are developing biomimetic polymeric materials for use as durable valve substitutives with native tissue like mechanical and hydrodynamic properties.

To begin, collect a fresh porcine cardiac specimen after cardiectomy. Dissect the pulmonary artery off the aorta with Metzenbaum scissors until ventricular tissue is visible. Then, dissect the right and the left coronary arteries, and ligate them using silk ties at their origin from the aortic sinuses without narrowing the sinuses.

Transect the coronary arteries distal to the silk ties. Using Metzenbaum scissors, incise the right ventricle between the aorta and the pulmonary artery at the base of the pulmonary valve. Beginning anteriorly, continue the incision circumferentially along the intraventricular septum to remove the right ventricle free wall.

Continue the incision posteriorly through the tricuspid valve annulus along the interatrial septum to remove all right atrial tissue. Next, using Metzenbaum scissors, incise the left atrium through the right pulmonary vein ostium parallel to the aorta. Continue this incision towards the anterolateral commissure of the mitral valve.

Trim excess left atrium tissue while maintaining the three-millimeter cuff of atrial tissue on the aorta and the mitral valve annulus circumferentially. Now, extend the incision onto the left ventricle through the anterolateral commissure of the mitral valve without damaging the anterolateral papillary muscle. Divide the chordae tendinae from the anterolateral papillary muscle to the posterior mitral valve leaflet preserving attachments to the anterior mitral valve leaflet.

Extend the incision to the apex of the heart. Trim excess left ventricle tissue below the papillary muscles, preserving both papillary muscles. After preparing the left ventricular outflow tract, or LVOT, trim any excess lymphatic, connective, or pulmonary artery tissue off the aorta.

Using Metzenbaum scissors, incise the superior aspect of the aortic arch from the descending aorta to the left subclavian artery. Continue the incision on the superior aspect of the aortic arch from the left subclavian artery to the brachiocephalic trunk. To cannulate the LVOT, insert the fixture into the LVOT under the anterior leaflet of the mitral valve.

Wrap the left ventricle free wall around the fixture and trim excess tissue to maintain a tight wrap around the fixture. Next, remove half the thickness of the left ventricle free wall starting at the interventricular septum. Trim one centimeter of the tissue off the superior corner of the left ventricle free wall wrap.

Place the fixture in the LVOT so the supporting rod attachment hole is one centimeter behind the left ventricle incision. Using one or two six-inch zip ties, fasten the anterior leaflet of the mitral valve to the fixture positioned between the chordae tendinae of the leaflet. Next, using a taper point needle, suture the cuff of the left atrium tissue on the aorta to the mitral valve annulus.

Continue the running stitch onto the left ventricle without tearing the tissue. Using Hagar dilators, measure the diameter of the aortic valve. Then, lift the specimen by grasping the aorta to identify the neutral position of the aorta.

Insert the pulse duplicator, or PD fixture, into the aorta, ensuring the rod attachment holes are aligned with the neutral position of the aorta. Verify the specimen's length by inserting the support rods into the attachment holes. Using one or two six-inch zip ties, secure the PD fixture to the aorta.

Then, using screws provided with the PD set, secure the support rods in place. Subsequently, secure the LVOT around the PD fixture using one or two eight-inch zip ties. Place the specimen in the PD and start the hydrodynamic testing.

The values for hydrodynamic testing of the native aortic valve were within the normal range with a mean regurgitation fraction of 5.74%Hydrodynamic testing values showed no significant differences between formalin and glutaraldehyde-fixed samples. After the Ozaki procedure, the values obtained with the control patch material suggested consistent valve replacement outcomes.