Symmetry! Bypass System Aortic Connector:A Star is Born!

For nearly thirty years, cardiac surgeons have rerouted blood around blockages in the coronary arteries by using blood vessels from other parts of the body and attaching them with needle and suture in order to restore circulation to the heart. Although cardiac surgery has evolved over the last three decades, it is important to note that one unfortunate statistic still remains: between one and five percent of the 400,000 Americans who undergo coronary artery bypass surgery each year will suffer some level of cerebrovascular event or stroke. This number approaches 10% as patients reach age 65 or greater. As alarming as these statistics are, an even larger number of patients who undergo coronary artery bypass surgery will suffer some form of cognitive deficit. Reported incidents range from 33% to 83%, and of these patients, up to 35% will have deficits that will persist for 12 months.¹ Most patients who experience neurocognitive effects such as attention deficits, loss of cognitive function or memory impairment will readily acknowledge that these unfortunate complications are less catastrophic than increasing loss of cardiac function. However, for some patients this debilitating loss of cognitive function can alter the quality of their life every bit as much as cardiac disease. A September 2000 New York Times article profiles one such patient, a very successful attorney in New Orleans and a member of several state and federal law committees who underwent coronary bypass surgery in 1989. ² Following his successful operation, he began to notice problems with his memory. Performing even simple tasks had also become noticeably difficult. When he inquired about this problem, his physician told him that this would be a transient event and should improve over the next 30 days. After returning to work a month later, he became increasingly frustrated with his inability to remember important information and events. He began searching for ways to enhance his memory function but was mostly unsuccessful, and tragically had to give up his law practice. As clinicians begin to investigate the extent of these post-surgical alterations in cognitive function, studies are suggesting that 10 to 50 percent or more of post-surgical bypass patients struggle on tests of language, memory and spatial relationship. The largest contributing factor to these neurologic complications has proven to be manipulation of the aortic wall during cardiac surgery using cross clamps and partial occlusion clamps. This can result in plaque embolization from atherosclerotic lesions of the ascending aorta. Until recently, the use of these clamps has been absolutely necessary to create the proximal end (anastomosis) of the saphenous vein bypass graft. The conventional suturing of the proximal end of these vein grafts requires placement of a partial occlusion clamp (known as side biting) on the section of aorta where the proximal end of the graft is to be placed. The proximal end is then cut at an angle in order to create a hood that is sutured to the aorta, creating an angled takeoff. Multiple graft placements require multiple clampings of the aorta, placing the patient at greater risk. ³ However, new technology now provides cardiac surgeons with a device that dramatically reduces the risk of these often-catastrophic neurologic events. The Symmetry! Bypass System Aortic Connector (St. Jude Medical, Minnetonka, MN) received FDA approval in May of 2001 and to date, there have been nearly 34,000 implants in patients during coronary bypass surgery. Approved for use with the saphenous vein to create the proximal anastomosis for each graft, the Symmetry Bypass System Aortic Connector uses no suture and eliminates the need for partial occlusion clamps during surgery. The Symmetry Bypass System Aortic Connector is a one-piece, laser cut section of nitinol that is molded into a star-shaped configuration. This creates a proximal anastomosis of precise size and geometry that cannot be duplicated using the traditional needle and suture method. Internal and external struts assist positioning and provide strength as the device is attached to the aortic wall. Race tracks then expand radially to create the ostial opening and a circumferential series of hooks attach the connector to the saphenous vein. With the Symmetry connector, the necessity for side-biting clamps are eliminated and the vein is deployed as follows: 1. First, a precise circular hole is cored through the aortic wall. 2. With the vein loaded onto the connector, the nose end is then inserted into the aortotomy and a button at the opposite end is pressed which releases the internal struts, allowing them to lie flat against the inner lumen of the aorta. 3. As the device is retracted, radial expansion of the racetracks occurs, creating the ostial opening. 4. The external struts fire next, to position and hold the connector in place in order to unsheath the remaining portion of the vein from the system. 5. Once the vein is attached proximally, a clip is placed at its distal end until it is sewn to the target vessel, where the clip is removed and blood flow is established. With the vein loaded for firing, the deployment time for the Symmetry connector is less than 60 seconds (compared to conventional suturing, which can take approximately 5-10 minutes). This represents a decrease in general anesthesia time and extracorporeal circulation for patients. Both of these factors have also proven to be major contributors to increasing risks for neurologic complications associated with cardiac surgery. ^1,3 It should be noted that the takeoff angle for a graft with the Symmetry connector is different than those created by conventional suturing. It mimics the 90-degree takeoff of the native coronary vasculature. In order to support and maintain this 90-degree placement, the ostia are generally in different locations than those of conventional sutured grafts. This might lead to the belief that they would be difficult to locate during angiography. However, the connector can be visualized under fluoroscopy, since it is made of the same material as intracoronary stents. It serves as its own location marker during coronary angiography, which makes the search for grafts substantially less tedious. Once deployed, the connector becomes endothelialized into the aortic wall and over the course of the next six months, a new and smooth neointimum will be formed. With the utilization of the Symmetry Bypass System Aortic Connector, concerns have been raised that connector technology would somehow increase the incidence of acute graft closure. The data collected to date, though, shows something quite different. For many years, the gold standard for graft patency has been the data that was collected and published by Fitzgibbons and Edmunds showing a 92.6% graft patency rate at one week, 85% patency at 30 days, and 75-85% patency at one year. ^{4 However, the patency rate decreases to 60% in the high-risk category of patients.5 There is a caveat to this data that should be mentioned. This data was collected from the late 1970s and the early 1980s in which the mean age of patients requiring CABG procedures was 54 years old. The data that has been collected to date on the use of Symmetry reports graft patency rates from 84-96% between 1 month and 1 year in a substantially older and higher-risk group of patients. 6,7 It has been documented that between 30 and 70% of patients needing coronary artery bypass surgery have significant atherosclerotic plaque of the ascending aorta that is not identified by palpation during surgery. 8 As the technology of interventional cardiology continues to evolve, the age of patients requiring bypass operations is certain to increase. With the aging process comes greater risk of plaque formation. Connector technology is still in its infancy, but it is clearly a large step in the right direction. The Symmetry Bypass System Aortic Connector technology allows less manipulation of the proximal aorta and the elimination of the side biting clamp, and offers cardiac surgeons another option for their patients who are at the greatest risk of micro embolic events during coronary artery bypass surgery.}

1. Fearn SJ, et al. Cerebral injury during cardiopulmonary bypass: emboli impair memory. J Thorac Cardiocasc Surg 2001;121:150-60.

2. Jauher S. Saving the heart can sometimes mean losing the memory. New York Times Sept 19, 2000.

3. Stump DA, Newman SP. Emboli detection during cardiopulmonary bypass. In: Tigler CH, Babikian VL, Gomez CR eds. Neurosonology 1996;252-5.

4. Edmunds LH. Techniques of Myocardial Revascularization. In: Edmunds LH (ed.) Cardiac Surgery in the Adult 1997;488-505.

5. Paz MA, Lupon J, Bosch E et al. Predictors of early saphenous vein aortocoronary bypass graft occlusion. Ann Thorac Surg 2000;56:101-06.

6. Mack M. Off pump coronary artery bypass with aortic connectors for the proximal anastomosis- The Dallas Experience. Presented at the 2002 meeting of Society of Thoracic Surgeons. Ft. Lauderdale FL.

7. Wiklund L. Angiographic results after the use of a sutureless aortic connector for proximal vein graft anastamosis. The Annals of Thoracic Surgery 2001;6:1993-4.

8. Davila-Roman VG et al. Intra-operative ultrasonographic evaluation of the ascending aorta in 100 consecutive patients undergoing cardiac surgery. Circulation 1991;84 SIII:47-53.