High Risk Patients
High risk patients can benefit from the less invasive technique of Aortic Valve Bypass. Currently, AVB surgery can be performed on a beating heart with little or no time on the heart/lung machine. The sternum is not cracked to gain access to the chest cavity, so healing time is significantly reduced.
Aortic Valve Bypass surgery is particularly attractive for high-risk patients with aortic stenosis, including "porcelain" (heavily calcified) ascending aorta, and redo surgery with open coronary bypass grafts, where aortic valve bypass surgery allows the surgeon to avoid reoperative sternotomy and manipulation/possible injury of the previously placed coronary bypass grafts. Recently published clinical results (ATS 2006) validate this approach. Aortic valve bypass surgery uses FDA-approved prosthetic valves within the conduit.
Current Procedure
In Aortic Valve Bypass surgery, a conduit is constructed from the apex of the left ventricle to the descending thoracic aorta. The conduit contains a bioprosthetic valve.
Instead of replacing the stenotic (narrowed) native valve, aortic valve bypass surgery bypasses the obstruction to left ventricular outflow. As such, blood flow exits the left ventricle by way of both the stenotic native valve and the AVB conduit. MRI flow studies have shown that approximately 70% of the blood flow exits via the AVB conduit and the remainder exits via the native valve.
As currently performed clinically, insertion of the apical left ventricle connector (LV connector) into the apex of the heart is the most difficult part of the aortic valve bypass (AVB) procedure and is performed in a relatively primitive fashion. LV connector insertion involves the use of available surgical tools to create a calibrated hole in the apex of the ventricle. Specifically, with the patient on cardiopulmonary bypass (CPB), a Foley catheter (a balloon) is inserted into the left ventricle via a small stab wound at the apex. The Foley catheter is inflated and used as a backstop to allow cutting and removal of an apical tissue plug by a sterilized cork borer or coring knife. As a separate step after the apical hole has been created, a Hancock LV connector is inserted and sutured in place - a procedure obviously associated with significant blood loss. Some surgeons avoid CPB by using a manual technique to rapidly insert the conduit, but any misstep can result in even greater blood loss.
Advantages
As performed clinically today, Aortic Valve Bypass Surgery offers several specific advantages over conventional aortic valve replacement, including:
- Avoidance of sternotomy: faster recovery
- Avoidance of aortic cross-clamping: AVB is a "beating heart" operation
- Cardiopulmonary bypass and cardioplegic arrest not required
- Brain protection: In the perioperative period, AVB avoids manipulation of the ascending aorta, debridement of the native calcific valve, cardiopulmonary bypass, and aortic cross-clamping, all of which are associated with stroke.
- Brain protection: In the long-term, aortic valve bypass protects the brain due to its unique blood flow pattern: 70 percent of left ventricular outflow occurs via the conduit, 30 percent via the native stenosed valve. NO blood flow to the brain flows across the prosthetic valve; hence the risk of brain thromboembolism (stroke) is minimized.
- Avoidance of patient-prosthesis mismatch
- No paravalvular leakage
- If the valve wears out, it can be readily replaced
- No injury to the heart's conduction system
- No post-op anticoagulation required
While Aortic Valve Bypass minimizes the risk of stroke, both conventional aortic valve replacement and percutaneous valve replacement increase the risk of stroke perioperatively and long term. Both of these procedures work at the site of the native valve where disruption of calcium deposits can cause small particles of calcium to embolize to the brain. Long term, emboli due to prosthetic valve disease are a chronic risk.
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