According to the World Health Organization (WHO) report The Global Burden of Disease1, ischaemic heart disease is currently the number one cause of death. Approximately 25% of the population over 75 years of age suffers from symptoms of cardiovascular diseases.
Coronary artery bypass grafting (CABG) has become one of the surgical procedures performed most often all over the world. Coronary artery bypass grafting has faced an unprecedented challenge in recent times from percutaneous therapies, but many centres now report a trend for more patients with multivessel disease to be referred for surgery than in recent years. This is likely to be explained, in part, by a growing acceptance of the long-term durability of revascularization by CABG, which contrasts with the higher requirements for reintervention after percutaneous therapies in randomized studies.2
Since the first CABG surgical procedure, preoperative as well as postoperative care has evolved. Patients undergoing CABG are now generally older and suffer from significantly more comorbidities. In addition, the choice of the most appropriate graft conduit has become an important issue, as novel techniques of graft handling and harvesting have been developed, with the aim of improving patency rates.3
The aim of this article is to give a short overview on the current state-of-the-art in CABG surgery – summarizing the scientific literature with the inclusion of our own institutional experience.
Saphenous vein conduits
Despite the fact that, in general, the graft patency of venous conduits is lower than that of arterial conduits, saphenous veins (SVs) are still frequently used as grafts in CABG surgery. Patency rates at 10 and 20 years are about 60% and 20% respectively. However, there is evidence that the low patency rates of SVs have significantly improved during the last few years. Better harvesting strategies, together with risk factor management and the use of statins, are thought to be the reasons why 5-year patency rates of nearly 80% for SVs grafted to the largest non-left anterior descending (LAD) vessel have been reported in some studies.3,4
Endoscopic vein harvesting (EVH) for CABG has increased significantly during the last decade. The main advantages of this technique are reduced wound area and decreased risk of wound complications. However, concerns have been raised regarding the patency rates of veins harvested endoscopically. Some studies5–6 have found that graft patency is reduced in comparison with open harvested veins. However, a closer look at these data shows that when EVH is performed by experienced surgeons, with a high caseload, it is a safe and reproducible technique which does not harm graft patency.5 Experience in our institution shows that after 20 cases the learning curve drops dramatically; thus, we recommend that experienced surgeons perform at least two EVH procedures a week to achieve persistent and satisfying results.
Arterial grafts – mammary arteries
Surgeons and cardiologists have been aware of the limitations of SV grafts for some time. Extensive arterial revascularisation has developed over the last 10 years. As the left internal thoracic artery has become the graft of choice for the LAD, there is growing evidence that two internal thoracic artery grafts are superior to the use of a single internal thoracic artery graft.
About 85–92% of left internal mammary artery (LIMA) grafts are patent at 15 years. The failure rate of right internal mammary artery (RIMA) grafts is overall, greater, but not significantly so, than that of LIMA grafts. However, when grafted to the LAD artery, the patency is similar. Innovative strategies have been developed to improve the number of distal anastomoses using sequential and composite internal thoracic grafts.
Bilateral mammary artery
The use of both mammary arteries should be considered, especially in younger patients, because of the improved patency rates and potential survival benefit. However, the use of both mammary arteries might result in higher rates of wound-healing disturbances.7
Harvesting of the internal mammary arteries
Traditionally, internal mammary arteries have been harvested as pedicels in order to minimize trauma and manipulation to the vessel. During the last few years, most surgeons and centres have switched to skeletonized preparations. This leads to more length and flexibility of the graft and preserves at least some perfusion of the sternal edge from the intercostal arteries, leading to fewer wound-healing complications.
Other arterial grafts
The radial artery graft introduced by Carpentier et al. in 19738 initially developed a poor reputation because of high failure rates, but was revisited by Acar et al.9 after the findings that many of these original grafts were widely patent at 6 years. Use of the radial artery continues to increase and has provided an additional arterial conduit that has advantages over other arterial grafts such as the gastroepiploic or inferior epigastric artery grafts. However, in the case of all arterial grafts, and especially grafts of the radial artery, it is crucial that the stenosis of the target vessel is highly significant (> 90%). Radial arteries with stenosis < 70% that anastomose with coronary arteries often become occluded because concurrent flow from the coronary system is too high.
Off-pump versus on-pump coronary artery bypass grafting
Cardiopulmonary bypass is one of the basic requirements for cardiac surgery. During the past 30 years, CABG was primarily was performed with the use of cardiopulmonary bypass (‘on pump’) with cardioplegic arrest. On-pump CABG was shown to improve ischaemic symptoms and prolong survival. In the 1990s, off-pump CABG was developed in order to reduce complications associated with cardiopulmonary bypass including systemic inflammatory response, myocardial depression, ischaemia–reperfusion injury, cerebral dysfunction and haemodynamic instability.
Initial clinical reports showed rather promising results; thus, an increasing number of surgeons started to perform off-pump CABG. Recently, the first prospective randomized trials comparing off-pump and on-pump CABG found that off-pump CABG is associated with significantly higher 1-year composite outcome [death or major complication (reoperation, new mechanical support, cardiac arrest, coma, stroke, renal failure)]. The proportion of patients with fewer grafts completed than was originally planned was higher with off-pump CABG than with on-pump. Follow-up angiography revealed lower graft patency in fewer patients receiving off-pump CABG than on-pump CABG.10
Nevertheless, there are centres with very experienced surgeons performing off-pump CABG with very satisfying results. A high level of experience and surgical skill seems to be necessary to achieve results comparable to on-pump CABG. Therefore, routine off-pump CABG should be performed only in centres with high caseload and experienced off-pumps surgeons. Despite these facts, basic off-pump techniques are a requirement for every cardiac surgeon. In patients with significant atherosclerotic changes of the ascending aorta, cross-clamping has to be avoided and off-pump CABG, or at least on-pump beating heart CABG with peripheral cannulation for cardiopulmonary bypass, has to be performed. In order to screen for such patients, we recommend preoperative computed tomography (CT) scans for every patient older than 65 years and patients with additional risk factors for artherosclerosis (e.g. peripheral or central arterial vascular disease) in order to rule out significant atherosclerotic pathology and adapt the surgical strategy accordingly.
Patients undergoing CABG today are generally older and suffer significantly more often from obesity, diabetes mellitus and peripheral artery disease. Furthermore, more surgeons try to use both mammary arteries in an increasing number of patients in order to improve graft patency and patient survival. Therefore, the risk of wound-healing disturbances has increased during the last few years. Postoperative wound disturbances following cardiothoracic surgery, most notably surgical site infection, are associated with increased morbidity, mortality and costs. Occurrence of sternal infection (mediastinitis) has been reported in up to 20% of cases; however, most studies report an incidence of 1–5%.11
There is no room for wound-healing complications in cardiac surgery today, and every effort has to be made to reduce the number of sternal wound-healing disturbances. Meticulous attention, careful soft tissue handling and excellent treatment of the sternum, including midline sternotomy and perfect sternotomy closure, are basic requirements for every cardiac surgeon.
There are some strategies that might reduce wound-healing problems in high-risk patients. Skeletonization of internal mammary arteries preserves sternal perfusion, but bone wax should be avoided in patients with risk factors for wound-healing disturbances. In patients with severe obesity (with a body mass index > 35 kg/m2), osteosynthesis by primary plating (Titanium Sternal Fixation System Synthes™, Synthes Inc.; West Chester, PA, USA) should be considered. Additional measures, such as application of autologous fibrin glue enriched with growth factors, may promote wound healing even further.12
Coronary artery bypass grafting is a standardized and highly reproducible surgical method with high long-term survival and graft patency rates. Nevertheless, the technique is still evolving, for example as a reaction to older and sicker patients undergoing CABG.
The most important developments of the last few years are the standard use of LIMA to LAD grafting, the general trend towards all arterial revascularisation strategies, skeletonization of mammary arteries and no-touch harvesting strategies of the grafts. Novel techniques such as endoscopic vein harvesting are important tools for decreasing morbidity after CABG; however, focused training and high caseload are crucial for the success of the operation. Off-pump CABG is an alternative approach for trained surgeons with a high caseload and is an indispensible strategy for patients with atherosclerotic ascending aortas. Preoperative CT of the ascending aorta should be performed in at least every patient older than 65 years and patients with additional risk factors for atherosclerosis. Wound-healing complications are an increasing problem as patients today suffer from significantly more comorbidities and risk factors for wound infection, but can be avoided by careful attention to surgical techniques and patient comorbidities.