Apicoaortic Conduit

Apicoaortic Conduit (AAC), also known as Aortic Valve Bypass (AVB), is a cardiothoracic surgical procedure that alleviates symptoms caused by blood flow obstruction from the left ventricle of the heart. Left ventricular outflow tract obstruction (LVOTO) is caused by narrowing of the aortic valve (aortic stenosis) and other valve disorders. AAC, or AVB, relieves the obstruction to blood flow by adding a bioprosthetic valve to the circulatory system to decrease the load on the aortic valve. When an apicoaortic conduit is implanted, blood continues to flow from the heart through the aortic valve. In addition, blood flow bypasses the native valve and exits the heart through the implanted valved conduit. The procedure is effective at relieving excessive pressure gradient across the natural valve. High pressure gradient across the aortic valve can be congenital or acquired. A reduction in pressure gradient results in relief of symptoms. Apicoaortic Conduit (AAC), also known as Aortic Valve Bypass (AVB), is a cardiothoracic surgical procedure that alleviates symptoms caused by blood flow obstruction from the left ventricle of the heart. Left ventricular outflow tract obstruction (LVOTO) is caused by narrowing of the aortic valve (aortic stenosis) and other valve disorders. AAC, or AVB, relieves the obstruction to blood flow by adding a bioprosthetic valve to the circulatory system to decrease the load on the aortic valve. When an apicoaortic conduit is implanted, blood continues to flow from the heart through the aortic valve. In addition, blood flow bypasses the native valve and exits the heart through the implanted valved conduit. The procedure is effective at relieving excessive pressure gradient across the natural valve. High pressure gradient across the aortic valve can be congenital or acquired. A reduction in pressure gradient results in relief of symptoms. The figure depicts a typical apicoaortic configuration with a left ventricle connector sutured to the apex of the heart, and a conduit containing a bioprosthetic valve anastomosed to the descending thoracic aorta. Blood exits the left ventricle either through the natural valve or the bypass conduit. The concept of an apicoaortic conduit to bypass valvular aortic stenosis (AS) was conceived by Carrel in 1910, and performed experimentally by Sarnoff and colleagues on dogs in 1955. In 1962-63, Templeton implanted prostheses similar to those originally described by Sarnoff in five patients with severe aortic valve stenosis; one patient survived more than 10 years. In 1975, Bernhard and coworkers reported a reoperation in which a conduit was implanted between the left ventricle and the thoracic aorta. The procedure was also developed in the late 1970s as a way to treat complex left ventricular outflow tract obstructions (LVOTO) in children and young adults. AAC is no longer performed on children as the Ross procedure has superseded it. Today, AAC is performed clinically on elderly aortic stenosis patients, and has gained in popularity in recent years. In the past 25 years, a number of case series on adults have been published. As of 2010, the estimated total number of AAC cases performed worldwide in the last 30 years is greater than 1500. The procedure has not been adopted widely because it is technically challenging and blood loss can be significant. The most difficult part of the procedure is the insertion of a left ventricle connector into the apex of the heart. AAC requires specialized implants and installation tools. Hancock Laboratories, now part of Medtronic (Minneapolis, MN), developed and released a set of left ventricle connectors, valved conduits, and installation trocars in the 1970s. The Hancock left ventricle connectors, with inner diameters of 12 to 22 mm, have been used clinically for the vast majority of AAC procedures reported in the literature. For the valved conduit, surgeons have used the Medtronic Hancock Model 105 or 150 valved conduits which contain a complete porcine aortic valve. Other surgeons have constructed valved conduits on the back table using a variety of bioprosthetic valves such as the Medtronic Freestyle valve. The Hancock trocars for creating a hole in the left ventricle are rarely used clinically. Surgeons typically assemble their own tools to core and remove a plug of muscle from the left ventricular wall. In 2011, Correx (Waltham, MA) released a complete kit for AVB with an installation tool that enables coring and insertion of a left ventricle connector on a beating heart while maintaining hemostasis. Cardiopulmonary bypass (CPB) is not required. The kit is CE Marked and available in Europe. Several cases have been done in Canada under the Special Access Programme. This kit is not currently available for use or sale in the United States. The general procedure has evolved over the years as surgeons gained experience and improved techniques. A video of an AVB procedure performed by Dr. Jim Gammie of the University of Maryland Medical Center can be found here. The patient is placed on the table in the supine position. Anesthesia is induced, and the patient is intubated with a double-lumen endotracheal tube, which facilitates one-lung ventilation and allows the surgeon to work within the left chest. The patient is positioned with his or her left side up (see figure). A left anterior-lateral thoracotomy is performed between the fifth and sixth ribs to expose the heart and provide access to the descending aorta. A portion of a rib may be removed to enable easier access and to minimize the chance of a rib fracture. The left lung is deflated and retracted.