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Coronary artery bypass grafting (CABG) has been shown to be an effective therapy for prolonging life and decreasing symptoms in appropriately selected patients with coronary artery disease (CAD). However, more recent advances in catheter-based therapies—specifically, drug-eluting stents—have resulted in fewer patients' choosing surgical bypass. Although many patients are well served by these exciting new options, others are perhaps less well served.
In this brief summary, I will focus on CABG, rather than compare it with various catheter-based therapies. In the United States, CABG includes, in nearly all cases, a left internal mammary artery graft (LIMA) to the left anterior descending coronary artery (LAD). The benefits of surgically bypassing the LAD with the LIMA are well known and have been reported in multiple studies. Not only does the LIMA graft prolong life and decrease symptoms better than any other therapy for CAD, but excellent data from Tatoulis and colleagues1 show that these benefits persist for the life of the graft and that graft patency extending beyond 10 and 15 years is commonplace.
With such good results, why are so fewer patients being referred for CABG? Arguably, the main factors that have contributed to decreased CABG referrals are the perceived morbidity associated with cardiopulmonary bypass (CPB) and sternotomy and the morbidity resulting from saphenous vein graft (SVG) attrition. However, technology currently under development might mitigate each of these issues.
Over the last decade, several new tools and techniques have evolved that enable surgeons who are skilled in their use to perform most CABG procedures without CPB. A number of prospective, randomized studies have now compared off-pump coronary artery bypass (OPCAB) with conventional CABG using CPB. Although individual studies vary somewhat, the consensus seems to be that the 2 techniques result in similar outcomes with respect to death, stroke, and major adverse cardiac events; however, OPCAB is associated with decreased postoperative blood loss and postoperative transfusion.2-7 In addition, certain high-risk groups, such as patients with aortic atheroma, renal insufficiency, or cirrhosis, might have better outcomes after OPCAB than after conventional CABG, although the supporting evidence for this is less well established.7-12
There are conflicting reports with respect to graft patency after OPCAB versus CABG with CPB. Although some studies have reported increased graft attrition and late major adverse cardiac events with OPCAB,13 others have reported equivalence.6,14–17
Although sternotomy is well tolerated and infection rates of 1% to 2% are commonly reported, a patient's desire to avoid having his or her “chest cracked” is understandable. Even with the aid of modern analgesia, the discomfort from a well-performed sternotomy is hard to ignore for 3 to 4 weeks, or longer. In addition, patients in our “body-conscious” society want, increasingly, to avoid an anterior chest scar. As a result, numerous new techniques have been developed in an effort to avoid sternotomy; many of these rely on a partial sternotomy or a small thoracotomy. These smaller incisions mitigate some of the concerns with full sternotomy and are very common in some surgeons' practices. Using modern tools and techniques, we can now perform a multivessel OPCAB through a 10-cm lateral thoracotomy with acceptable results.
Saphenous vein graft attrition is another area of active research and development. It is well accepted that SVG patency is inferior to that of the mammary artery. Data from the 1970s suggested that approximately 90% of SVGs were patent after 1 year and that patency remained fairly stable for 5 years. Subsequently, approximately 10% of grafts became occluded each year, which left only 50% of SVGs patent at 10 years; and 50% of these had significant disease, as seen during angiography.18,19 Although this study has not been repeated recently, there are several reasons to suspect that SVG patency is worse in the modern era. Because of advances in catheter-based therapies, patients who are referred for CABG tend to be older and sicker, and to have more diffuse atherosclerosis.
To date, efforts to modify the SVG biologically before grafting have not been successful.20,21 Recent efforts to support the SVG externally with a fine nitinol mesh have, however, yielded interesting results in primate experiments.22,23 The hypothesis is that by decreasing SVG diameter and increasing the effective thickness of the wall, the mesh reduces wall tension, which is believed by many to be a primary trigger for the development of intimal hyperplasia and the acceleration of graft loss. The clinical evaluation of these technologies is ongoing and promising.
Perhaps the most intriguing technologic advance with respect to avoiding sternotomy is the field of surgical robotics. A highly evolved robotic system, the da Vinci® Si HD™ Surgical System (Intuitive Surgical, Inc.; Sunnyvale, Calif), can enable a surgeon to gain access to the heart and LIMA without opening the chest. Instead, 4 incisions between the ribs, each one-half inch in length, enable robotic instruments and a video scope to be introduced into the chest. The surgeon sits at a robotic console and can see inside the patient's chest through high-definition, 3-dimensional optics. The console is connected electronically to the bedside robot, enabling the surgeon to manipulate the robotic instruments and the scope just as one would manipulate conventional, hand-held surgical instruments. The robotic system provides image magnification and enables the surgeon's movements to be scaled and filtered, which provides superhuman precision but eliminates sense of touch. A rapid exchange system makes it easy for a bedside nurse to change the robotic instrument in use from forceps to scissors, to needle driver, to electrocautery.
Using the da Vinci System, skilled surgeons can harvest the LIMA from the back of the sternum, open the pericardium, stabilize the segment of the LAD chosen for grafting, and perform the anastomosis between the LIMA and LAD on a beating heart. Despite numerous reports of success,24-27 this technology is far from mainstream. A committed team, however, can obtain excellent results. One of the challenges associated with this technique is performing the actual anastomosis. Ways to automate this aspect of the procedure are evolving.
Although a few leaders in the field of robotic surgery have combined the use of a surgical robot and an automated anastomotic device to perform faster, more reproducible, closed-chest, beating-heart CABG, this procedure is still considered experimental by most cardiothoracic surgeons. Several groups have attempted to develop automated anastomotic devices that can reproducibly construct a “one-shot” hemostatic connection between the graft and the coronary artery. Unfortunately, none of these extremely creative devices, including ones that use strong rare-earth magnet clips or locking nitinol frames,28 has functioned well enough to obtain approval for use in the United States. In November 2006, however, the U.S. Food and Drug Administration did approve the automated C-Port xA® Distal Anastomosis System (Cardica, Inc.; Redwood City, Calif). This device uses compressed carbon dioxide to actuate a mechanism that anastomoses the end of the bypass graft to the target artery by firing 13 small staples at the same time that it precisely incises the target artery. Angiograms obtained up to 2 years postoperatively show equivalent mid-term graft patency in comparing the automated and hand-sewn anastomoses. The skill required and the expense involved have, to date, limited widespread application. Further refinement and simplification, however, might one day render this combination a valuable option for patients with CAD.
Summary. By continuing to develop and refine new technology to improve outcomes after CABG, cardiac surgeons hope to maintain or increase the use of surgical bypass so that patients will continue to enjoy the benefits of this valuable therapy, including the long-term patency of LIMA-to-LAD grafts.
Address for reprints: William E. Cohn, MD, Director, Minimally Invasive Surgical Technology, MC 1–114A, P.O. Box 20345, Texas Heart Institute at St. Luke's Episcopal Hospital, Houston, TX 77225
Presented at the 9th Texas Update in Cardiovascular Advancements; Houston, Texas; 4–5 December 2009
Program Director: James T. Willerson, MD