- Email: [email protected]
Coronary artery bypass surgery
REVASCULARIZATION
Coronary artery bypass surgery
every year worldwide. For the last three decades, CABG has remained the ‘gold standard’ treatment for patients with multivessel CAD and is the most extensively studied surgical procedure with follow-up data extending to several decades. It is highly effective in relieving the symptoms of ischaemic heart disease and improves life expectancy in certain anatomical subsets; these benefits are magnified in patients with more severe disease and those with impaired left ventricular function. Furthermore, CABG is a remarkably safe therapy. Improvements in medical, anaesthetic and surgical management have ensured static mortality rates over the last decade despite increasing application to an ageing and sicker patient population. Relief from angina and improved quality of life are achieved in the majority of patients but the main long-term drawback is vein graft failure leading to recurrent angina, myocardial infarction and death. The annual attrition rate of vein grafts is about 2e4% leading to recurrent angina in 20% of patients at 5 years and 40% at 10 years. However, the widespread use of arterial grafting, anti-platelet agents and statins is likely to improve graft longevity and subsequent outcome.
Yasir Abu-Omar David P Taggart
Abstract For over four decades, coronary artery surgery has been shown to relieve angina and extend life expectancy in patients with severe coronary artery disease and to date it remains the gold standard method for coronary revascularization especially in patients with the most severe disease. Pioneered in the 1960s, it has since grown to become the most commonly performed and most intensively studied surgical procedure in the world. Although increasingly challenged by percutaneous techniques using stents, the last decade has witnessed a significant reduction in surgical mortality (currently around 1% in elective patients) and morbidity despite being applied in an increasingly older and sicker population. The use of arterial grafts, especially the left internal mammary artery, has resulted in significant improvements in long-term patency and clinical outcome. More recent technical advances include beating heart (off-pump) surgery and minimally invasive techniques.
Indications Randomized trials performed in the 1970s confirmed the superiority of CABG over medical therapy with respect to relief from angina and improved quality of life in symptomatic patients. The main trials included: the Coronary Artery Surgery Study (CASS), the Veteran’s Administration Coronary Artery Bypass Trial, and the European Coronary Artery Bypass Trial. These studies served to define the population subsets most likely to derive prognostic benefit from surgery. A landmark meta-analysis confirmed the benefits of CABG, especially in high-risk patients.1 The clinical indications for CABG are listed in Table 1.2
Keywords conduits; coronary artery bypass; ischaemic heart disease; off-pump; revascularization
Coronary artery disease (CAD) represents a major health burden in the western world. It accounts for around 95,000 deaths in the UK each year, making it the most common cause of death (one in five men and one in seven women die as a consequence of CAD). Around 2.1 million men and 1.3 million women (3.4 million adults) in the UK have suffered angina and/or a heart attack. Worldwide, cardiovascular disease results in over 19 million deaths and CAD accounts for the majority. Around 100,000 revascularization procedures (>77,000 percutaneous and >20,000 coronary artery bypass grafting (CABG) procedures) were performed in the UK in 2008. Revascularization (either surgical or percutaneous) improves symptoms and quality of life in patients with CAD but only surgical revascularization has been shown to also improve life expectancy.
Risk assessment Several systems of stratification can be used to estimate the risk associated with cardiac surgery. Risk stratification defines the ability to predict outcomes from a given intervention by arranging patients according to the severity of their illness. Thus, outcomes from surgery may be compared to those predicted by risk models. Risk stratification also serves to estimate the risks of surgery in individual patients, allowing careful comparison with the potential or perceived benefits. The most commonly used risk stratification systems include: Parsonnet e this model was originally developed in the USA in 1985. Recent advances in clinical practice mean that this now tends to overestimate the risk of mortality associated with cardiac surgery. Euroscore e developed in Europe and widely used in the UK, this is a better predictor of risk than Parsonnet and readily used at the patients’ bedside (Table 2). As described above, it consistently overestimates risk and a modified version is in current development. Society of Thoracic Surgeons e used in the USA, this extensive system provides measures of both mortality and morbidity.
Coronary artery bypass grafting CABG is the most common surgical procedure performed on the heart, with approximately half a million operations performed
Yasir Abu-Omar DPhil MRCS is a specialist registrar at Papworth Hospital, Cambridge, UK. Competing interests: none declared. David P Taggart MD(Hons) PhD FRCS is currently Professor of Cardiovascular Surgery at the University of Oxford and Consultant Cardiac Surgeon at the John Radcliffe Hospital, Oxford, UK. Competing interests: none declared.
MEDICINE 38:8
Conduits for CABG The principle of CABG is to bypass diseased segments of the coronary circulation using arterial and venous conduits e the 446
Ó 2010 Elsevier Ltd. All rights reserved.
REVASCULARIZATION
used with varying results. Performance is judged on the basis of long-term patency and effect on clinical outcome. Patient factors, including coronary anatomy, also play an important part in the decision-making process. Figure 1 shows some of the graft configurations that may be used in CABG.
Indications for surgery in ischaemic heart disease Indications for myocardial revascularization Relief of angina (stable or unstable) which is unresponsive to medical therapy. Severe symptoms despite optimal medical therapy. Congestive heart failure complicating acute myocardial ischaemia or severe coronary artery disease. Cardiogenic shock after myocardial infarction. Anatomic considerations indicating prognostic benefit of CABG Left main coronary artery stenosis >50%. Left main equivalent disease: significant stenosis (>70%) of proximal LAD and proximal circumflex artery. Three-vessel coronary artery disease with left ventricular dysfunction (left ventricular ejection fraction [LVEF] <50%). Two-vessel disease including a proximal LAD stenosis combined with left ventricular dysfunction. Other indications Mechanical complications of myocardial infarction including postinfarction ventricular septal defect, mitral regurgitation secondary to papillary muscle dysfunction, and ventricular rupture.
Left internal mammary artery Initially used in the early 1970s, popularity of the LIMA conduit has grown remarkably following reports demonstrating superior patency rates (exceeding 90% at 10 years) and patient survival in comparison with saphenous vein grafts. The Cleveland clinic group reported 11% improvement in 10-year survival in patients receiving LIMA to LAD3 and this is now the conduit of choice to the diseased LAD. Bilateral internal mammary arteries The superior performance of the LIMA leads intuitively to the assumption that use of bilateral IMA grafts (BIMA) should maximize benefit. To date, the most powerful supporting evidence comes from a meta-analysis of over 15,000 patients.4 However, routine use of BIMA should be weighed against potential drawbacks which include devascularization of the sternum (with resulting increase in the risk of wound complications, especially in obese diabetic patients), prolonged operation time and technical challenges associated with its use. The only randomized trial (Arterial Revascularization Trial e ART) comparing the value of BIMA and single
Table 1
most frequently used are the left internal mammary artery (LIMA) and the long saphenous vein. Several other options (radial artery, gastroepiploic artery, cephalic vein) have been
The additive EUROSCORE (www.euroscore.org) Patient-related factors Age Sex Chronic pulmonary disease Extracardiac arteriopathy Neurological dysfunction Previous cardiac surgery Serum creatinine Active endocarditis Critical pre-operative state
Cardiac-related factors Unstable angina LV dysfunction Recent myocardial infarct Pulmonary hypertension Operation-related factors Emergency Other than isolated CABG Surgery on the thoracic aorta Post-infarct septal rupture
Per 5 years or part thereof over 60 years Female Long-term use of bronchodilators or corticosteroids for lung disease Any one or more of the following: claudication, carotid occlusion or > 50% stenosis, previous or planned intervention on the abdominal aorta, limb arteries or carotids Severely affecting ambulation or day-to-day functioning Requiring opening of the pericardium > 200 mmol/L Patient still receiving antibiotic treatment for endocarditis at the time of surgery Any one or more of the following: ventricular tachycardia or fibrillation or aborted sudden death, pre-operative cardiac massage, pre-operative ventilation before arrival in the anaesthetic room, pre-operative inotropic support, intra-aortic balloon counterpulsation or pre-operative acute renal failure (anuria or oliguria < 10 ml/h)
Score 1 1 1 2 2 3 2 3 3
Angin a at rest requiring IV nitrates until arrival in the anaesthetic room Moderate (LVEF 30 _ 50%) Poor (LVEF < 30%) < 90 days Pulmonary artery systolic pressure > 60 mmH g
2 1 3 2 2
Carried out before the beginning of the next working day Major cardiac procedure other than or in addition to CABG Disorder of ascending arch or descending aorta
2 2 3 4
Table 2
MEDICINE 38:8
447
Ó 2010 Elsevier Ltd. All rights reserved.
REVASCULARIZATION
Different graft configurations in coronary artery bypass surgery a
b
Internal mammary artery
c
Radial artery
d
Saphenous vein graft
Note that with configuration B and C there is no proximal graft anastomosis to the aorta, i.e. composite grafting. This minimizes manipulation of the aorta and reduces the risk of stroke.
Figure 1
bypass (CPB) provides an artificial circulation, bypassing the heart and lungs allowing surgery to be performed in a stationary, bloodless operating field. However, while modern CPB remains very safe, it has some disadvantages. A systemic inflammatory response syndrome resulting from contact of blood with the artificial circuit can potentially cause multi-organ dysfunction, especially in higher risk patients. In addition, use of CPB involves manipulation of the aorta which may cause embolism of atheromatous debris and result in stroke.
IMA has been recently completed with reports due in the near future.5 Long saphenous vein The long saphenous vein was first used as a conduit for CABG in the 1960s and remains the most commonly used conduit. It is usually harvested using an open technique, but minimally invasive approaches are increasingly used with the aim of reducing morbidity. Patency rates at 10 years are around 50% but this may have improved in recent years with increased use of secondary preventative measures including anti-platelet agents and statins.
Off-pump CABG Recent years have witnessed growing interest in the practice of off-pump (‘beating heart’) coronary artery surgery to minimize the potential deleterious effects of CPB, especially in higher-risk patients.6 Improved stabilizing devices permit complete coronary revascularization and the avoidance of CPB in a progressively older surgical population. These attractions and consequent reduction in hospital costs have resulted in about 20% of CABG procedures now being performed in this way. However, offpump CABG is more technically demanding than conventional techniques and some have questioned the completeness of revascularization and quality of the anastomoses performed on the beating heart. Current evidence indicates that off-pump surgery is a very safe and an effective alternative to conventional CABG in skilled hands and should probably be increasingly used in high-risk groups, especially those with significant aortic atherosclerosis and high risk or perioperative stroke. In low-risk patients, however, CPB remains safe and completeness of revascularization is of paramount importance.6
Radial artery This conduit was first used in the 1970s but soon abandoned following an observed risk of increased morbidity. Improved harvesting techniques, use of agents to prevent vasospasm and demonstration of good long-term patency rates have led to a resurgence of interest in its use. Advantages include the low morbidity associated with harvesting and the avoidance of leg incision, which allows earlier post-operative mobility. Other conduits The short saphenous and cephalic veins have also been used when the long saphenous vein is unavailable. Both have reduced patency rates compared to the long saphenous vein and their routine use is not recommended. Use of other arterial grafts has also been reported (inferior epigastric and gastroepiploic arteries) e they offer no additional benefits and have limited use in practice. Cryo-preserved venous homografts and bovine mammary arteries have very low patency rates and are seldom used.
Surgical considerations
Minimally invasive direct coronary artery surgery This technique performed via a mini-left anterior thoracotomy is technically demanding but reduces traumatic injury to the patient. It is applicable only in a small subset of patients with one- or two-
Cardiopulmonary bypass The introduction of extracorporeal circulation in the 1950s heralded the practice of modern cardiac surgery. Cardiopulmonary
MEDICINE 38:8
448
Ó 2010 Elsevier Ltd. All rights reserved.
REVASCULARIZATION
vessel disease (usually including the LAD) and can also be used as part of a hybrid procedure in which patients undergo complete revascularization using a combination of this minimally invasive surgical procedure and percutaneous coronary intervention.
cases which are resistant to medical therapy or associated with haemodynamic compromise. Renal failure requiring temporary post-operative renal replacement therapy affects 1e5% of patients and is associated with increased mortality and morbidity. Causes include hypoperfusion, microembolism and a systemic inflammatory response syndrome. Wound infections are usually superficial but may involve the whole sternum and cause mediastinitis in 1% of patients. Risk factors include advanced age, diabetes mellitus, corticosteroid use, high body mass index, bilateral internal mammary artery grafting and need for re-exploration. Treatment depends on the condition of the patient and extent of infection. Antibiotic therapy may be sufficient for superficial infection but surgical debridement and reconstruction may be necessary for deep infection.
Robotic surgery Advances in surgical technique and technology have led to the use of robotic devices to achieve coronary revascularization with reduction in the morbidity associated with surgical trauma. The techniques are still in development and available to only a small proportion of surgical candidates at specialized centres. However, their use is likely to increase with greater experience and wider availability. Re-do CABG Re-do surgery is associated with a significant mortality and morbidity, and is technically more Principal benefits are the reduction of symptoms, alternatives such as percutaneous intervention exhausted before re-do surgery is considered.
increase in challenging. but feasible should be
Summary CABG is a safe and effective procedure which relieves the symptoms of angina and improves survival in patients with left main stem or three-vessel coronary artery disease. These benefits are further increased in those with impaired left ventricular function. Although the place of CABG has been recently challenged by percutaneous coronary intervention, recent trials demonstrate that surgical revascularization remains the gold standard in patients with complex coronary artery disease.7 Continued improvements in cardiac surgical outcomes will make coronary surgery even safer for future generations. A
Complications Mortality Peri-operative mortality is currently <2% and this figure has remained stable in recent years despite an increasingly older and sicker patient population. Contributory factors include improved surgical and anaesthetic techniques, better peri-operative medical management, and the monitoring and public reporting of surgical performance. Survival outcome for all 114,300 CABG operations performed in the UK over the 5-year period 2004e2008 has been recently published (www.scts.org). Overall hospital mortality was 1.8%, but higher (2.6%) in the 33,000 (30%) urgent patients than the 78,000 (70%) elective patients (1.1%). Similarly, 5-year survival in the two subgroups was 85% and 90%, respectively. Mortality rates were also higher in patients with diabetes mellitus (1 month 2.6%, 5-year survival 85%) and those with left main stem disease (1 month 2.5%, 5-year survival 86%).
REFERENCES 1 Yusuf S, Zucker D, Peduzzi P, et al. Effect of coronary artery bypass graft surgery on survival: overview of 10-year results from randomised trials by the Coronary Artery Bypass Graft Surgery Trialists Collaboration. Lancet 1994; 344: 563e70. 2 Eagle KA, Guyton RA, Davidoff R, et al. ACC/AHA 2004 guideline update for coronary artery bypass graft surgery: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Committee to Update the 1999 Guidelines for Coronary Artery Bypass Graft Surgery). Circulation 2004; 110: e340e437. 3 Loop FD, Lytle BW, Cosgrove DM, et al. Influence of the internalmammary-artery graft on 10-year survival and other cardiac events. N Engl J Med 1986; 314: 1e6. 4 Taggart DP, D’Amico R, Altman DG. Effect of arterial revascularisation on survival: a systematic review of studies comparing bilateral and single internal mammary arteries. Lancet 2001; 358: 870e5. 5 Taggart DP, Lees B, Gray A, Altman DG, Flather M, Channon K. Protocol for the Arterial Revascularisation Trial (ART). A randomised trial to compare survival following bilateral versus single internal mammary grafting in coronary revascularisation [ISRCTN46552265]. Trials 2006; 7: 7. 6 Abu-Omar Y, Taggart DP. The present status of off-pump coronary artery bypass grafting. Eur J Cardiothorac Surg 2009; 36: 312e21. 7 Serruys PW, Morice MC, Kappetein AP, et al. Percutaneous coronary intervention versus coronary-artery bypass grafting for severe coronary artery disease. N Engl J Med 2009; 360: 961e72.
Morbidity Cardiac surgery using CPB is associated with disturbed haemostasis and platelet function which may lead to post-operative bleeding. Around 1e2% of patients require surgical re-exploration for persistent bleeding, pericardial collection or tamponade. Stroke affects around 1% of patients e associated risk factors include advanced age, hypertension, diabetes mellitus and a previous history of stroke. More subtle cerebral injury in the form of confusion or cognitive impairment affects a third of patients early after surgery. Myocardial injury occurs to a variable extent and cardiac enzyme release can be identified in the majority of patients following cardioplegic arrest. However, lower levels observed using off-pump techniques do not necessarily translate directly into improved measures of clinical outcome. Atrial fibrillation (AF) affects one third of patients in the postoperative period with a peak incidence at 2e3 days. Treatment involves correction of serum electrolytes, appropriate antiarrhythmic medication and anticoagulation. Most cases resolve spontaneously but DC cardioversion should be considered in
MEDICINE 38:8
449
Ó 2010 Elsevier Ltd. All rights reserved.
Coronary artery bypass surgery
every year worldwide. For the last three decades, CABG has remained the ‘gold standard’ treatment for patients with multivessel CAD and is the most extensively studied surgical procedure with follow-up data extending to several decades. It is highly effective in relieving the symptoms of ischaemic heart disease and improves life expectancy in certain anatomical subsets; these benefits are magnified in patients with more severe disease and those with impaired left ventricular function. Furthermore, CABG is a remarkably safe therapy. Improvements in medical, anaesthetic and surgical management have ensured static mortality rates over the last decade despite increasing application to an ageing and sicker patient population. Relief from angina and improved quality of life are achieved in the majority of patients but the main long-term drawback is vein graft failure leading to recurrent angina, myocardial infarction and death. The annual attrition rate of vein grafts is about 2e4% leading to recurrent angina in 20% of patients at 5 years and 40% at 10 years. However, the widespread use of arterial grafting, anti-platelet agents and statins is likely to improve graft longevity and subsequent outcome.
Yasir Abu-Omar David P Taggart
Abstract For over four decades, coronary artery surgery has been shown to relieve angina and extend life expectancy in patients with severe coronary artery disease and to date it remains the gold standard method for coronary revascularization especially in patients with the most severe disease. Pioneered in the 1960s, it has since grown to become the most commonly performed and most intensively studied surgical procedure in the world. Although increasingly challenged by percutaneous techniques using stents, the last decade has witnessed a significant reduction in surgical mortality (currently around 1% in elective patients) and morbidity despite being applied in an increasingly older and sicker population. The use of arterial grafts, especially the left internal mammary artery, has resulted in significant improvements in long-term patency and clinical outcome. More recent technical advances include beating heart (off-pump) surgery and minimally invasive techniques.
Indications Randomized trials performed in the 1970s confirmed the superiority of CABG over medical therapy with respect to relief from angina and improved quality of life in symptomatic patients. The main trials included: the Coronary Artery Surgery Study (CASS), the Veteran’s Administration Coronary Artery Bypass Trial, and the European Coronary Artery Bypass Trial. These studies served to define the population subsets most likely to derive prognostic benefit from surgery. A landmark meta-analysis confirmed the benefits of CABG, especially in high-risk patients.1 The clinical indications for CABG are listed in Table 1.2
Keywords conduits; coronary artery bypass; ischaemic heart disease; off-pump; revascularization
Coronary artery disease (CAD) represents a major health burden in the western world. It accounts for around 95,000 deaths in the UK each year, making it the most common cause of death (one in five men and one in seven women die as a consequence of CAD). Around 2.1 million men and 1.3 million women (3.4 million adults) in the UK have suffered angina and/or a heart attack. Worldwide, cardiovascular disease results in over 19 million deaths and CAD accounts for the majority. Around 100,000 revascularization procedures (>77,000 percutaneous and >20,000 coronary artery bypass grafting (CABG) procedures) were performed in the UK in 2008. Revascularization (either surgical or percutaneous) improves symptoms and quality of life in patients with CAD but only surgical revascularization has been shown to also improve life expectancy.
Risk assessment Several systems of stratification can be used to estimate the risk associated with cardiac surgery. Risk stratification defines the ability to predict outcomes from a given intervention by arranging patients according to the severity of their illness. Thus, outcomes from surgery may be compared to those predicted by risk models. Risk stratification also serves to estimate the risks of surgery in individual patients, allowing careful comparison with the potential or perceived benefits. The most commonly used risk stratification systems include: Parsonnet e this model was originally developed in the USA in 1985. Recent advances in clinical practice mean that this now tends to overestimate the risk of mortality associated with cardiac surgery. Euroscore e developed in Europe and widely used in the UK, this is a better predictor of risk than Parsonnet and readily used at the patients’ bedside (Table 2). As described above, it consistently overestimates risk and a modified version is in current development. Society of Thoracic Surgeons e used in the USA, this extensive system provides measures of both mortality and morbidity.
Coronary artery bypass grafting CABG is the most common surgical procedure performed on the heart, with approximately half a million operations performed
Yasir Abu-Omar DPhil MRCS is a specialist registrar at Papworth Hospital, Cambridge, UK. Competing interests: none declared. David P Taggart MD(Hons) PhD FRCS is currently Professor of Cardiovascular Surgery at the University of Oxford and Consultant Cardiac Surgeon at the John Radcliffe Hospital, Oxford, UK. Competing interests: none declared.
MEDICINE 38:8
Conduits for CABG The principle of CABG is to bypass diseased segments of the coronary circulation using arterial and venous conduits e the 446
Ó 2010 Elsevier Ltd. All rights reserved.
REVASCULARIZATION
used with varying results. Performance is judged on the basis of long-term patency and effect on clinical outcome. Patient factors, including coronary anatomy, also play an important part in the decision-making process. Figure 1 shows some of the graft configurations that may be used in CABG.
Indications for surgery in ischaemic heart disease Indications for myocardial revascularization Relief of angina (stable or unstable) which is unresponsive to medical therapy. Severe symptoms despite optimal medical therapy. Congestive heart failure complicating acute myocardial ischaemia or severe coronary artery disease. Cardiogenic shock after myocardial infarction. Anatomic considerations indicating prognostic benefit of CABG Left main coronary artery stenosis >50%. Left main equivalent disease: significant stenosis (>70%) of proximal LAD and proximal circumflex artery. Three-vessel coronary artery disease with left ventricular dysfunction (left ventricular ejection fraction [LVEF] <50%). Two-vessel disease including a proximal LAD stenosis combined with left ventricular dysfunction. Other indications Mechanical complications of myocardial infarction including postinfarction ventricular septal defect, mitral regurgitation secondary to papillary muscle dysfunction, and ventricular rupture.
Left internal mammary artery Initially used in the early 1970s, popularity of the LIMA conduit has grown remarkably following reports demonstrating superior patency rates (exceeding 90% at 10 years) and patient survival in comparison with saphenous vein grafts. The Cleveland clinic group reported 11% improvement in 10-year survival in patients receiving LIMA to LAD3 and this is now the conduit of choice to the diseased LAD. Bilateral internal mammary arteries The superior performance of the LIMA leads intuitively to the assumption that use of bilateral IMA grafts (BIMA) should maximize benefit. To date, the most powerful supporting evidence comes from a meta-analysis of over 15,000 patients.4 However, routine use of BIMA should be weighed against potential drawbacks which include devascularization of the sternum (with resulting increase in the risk of wound complications, especially in obese diabetic patients), prolonged operation time and technical challenges associated with its use. The only randomized trial (Arterial Revascularization Trial e ART) comparing the value of BIMA and single
Table 1
most frequently used are the left internal mammary artery (LIMA) and the long saphenous vein. Several other options (radial artery, gastroepiploic artery, cephalic vein) have been
The additive EUROSCORE (www.euroscore.org) Patient-related factors Age Sex Chronic pulmonary disease Extracardiac arteriopathy Neurological dysfunction Previous cardiac surgery Serum creatinine Active endocarditis Critical pre-operative state
Cardiac-related factors Unstable angina LV dysfunction Recent myocardial infarct Pulmonary hypertension Operation-related factors Emergency Other than isolated CABG Surgery on the thoracic aorta Post-infarct septal rupture
Per 5 years or part thereof over 60 years Female Long-term use of bronchodilators or corticosteroids for lung disease Any one or more of the following: claudication, carotid occlusion or > 50% stenosis, previous or planned intervention on the abdominal aorta, limb arteries or carotids Severely affecting ambulation or day-to-day functioning Requiring opening of the pericardium > 200 mmol/L Patient still receiving antibiotic treatment for endocarditis at the time of surgery Any one or more of the following: ventricular tachycardia or fibrillation or aborted sudden death, pre-operative cardiac massage, pre-operative ventilation before arrival in the anaesthetic room, pre-operative inotropic support, intra-aortic balloon counterpulsation or pre-operative acute renal failure (anuria or oliguria < 10 ml/h)
Score 1 1 1 2 2 3 2 3 3
Angin a at rest requiring IV nitrates until arrival in the anaesthetic room Moderate (LVEF 30 _ 50%) Poor (LVEF < 30%) < 90 days Pulmonary artery systolic pressure > 60 mmH g
2 1 3 2 2
Carried out before the beginning of the next working day Major cardiac procedure other than or in addition to CABG Disorder of ascending arch or descending aorta
2 2 3 4
Table 2
MEDICINE 38:8
447
Ó 2010 Elsevier Ltd. All rights reserved.
REVASCULARIZATION
Different graft configurations in coronary artery bypass surgery a
b
Internal mammary artery
c
Radial artery
d
Saphenous vein graft
Note that with configuration B and C there is no proximal graft anastomosis to the aorta, i.e. composite grafting. This minimizes manipulation of the aorta and reduces the risk of stroke.
Figure 1
bypass (CPB) provides an artificial circulation, bypassing the heart and lungs allowing surgery to be performed in a stationary, bloodless operating field. However, while modern CPB remains very safe, it has some disadvantages. A systemic inflammatory response syndrome resulting from contact of blood with the artificial circuit can potentially cause multi-organ dysfunction, especially in higher risk patients. In addition, use of CPB involves manipulation of the aorta which may cause embolism of atheromatous debris and result in stroke.
IMA has been recently completed with reports due in the near future.5 Long saphenous vein The long saphenous vein was first used as a conduit for CABG in the 1960s and remains the most commonly used conduit. It is usually harvested using an open technique, but minimally invasive approaches are increasingly used with the aim of reducing morbidity. Patency rates at 10 years are around 50% but this may have improved in recent years with increased use of secondary preventative measures including anti-platelet agents and statins.
Off-pump CABG Recent years have witnessed growing interest in the practice of off-pump (‘beating heart’) coronary artery surgery to minimize the potential deleterious effects of CPB, especially in higher-risk patients.6 Improved stabilizing devices permit complete coronary revascularization and the avoidance of CPB in a progressively older surgical population. These attractions and consequent reduction in hospital costs have resulted in about 20% of CABG procedures now being performed in this way. However, offpump CABG is more technically demanding than conventional techniques and some have questioned the completeness of revascularization and quality of the anastomoses performed on the beating heart. Current evidence indicates that off-pump surgery is a very safe and an effective alternative to conventional CABG in skilled hands and should probably be increasingly used in high-risk groups, especially those with significant aortic atherosclerosis and high risk or perioperative stroke. In low-risk patients, however, CPB remains safe and completeness of revascularization is of paramount importance.6
Radial artery This conduit was first used in the 1970s but soon abandoned following an observed risk of increased morbidity. Improved harvesting techniques, use of agents to prevent vasospasm and demonstration of good long-term patency rates have led to a resurgence of interest in its use. Advantages include the low morbidity associated with harvesting and the avoidance of leg incision, which allows earlier post-operative mobility. Other conduits The short saphenous and cephalic veins have also been used when the long saphenous vein is unavailable. Both have reduced patency rates compared to the long saphenous vein and their routine use is not recommended. Use of other arterial grafts has also been reported (inferior epigastric and gastroepiploic arteries) e they offer no additional benefits and have limited use in practice. Cryo-preserved venous homografts and bovine mammary arteries have very low patency rates and are seldom used.
Surgical considerations
Minimally invasive direct coronary artery surgery This technique performed via a mini-left anterior thoracotomy is technically demanding but reduces traumatic injury to the patient. It is applicable only in a small subset of patients with one- or two-
Cardiopulmonary bypass The introduction of extracorporeal circulation in the 1950s heralded the practice of modern cardiac surgery. Cardiopulmonary
MEDICINE 38:8
448
Ó 2010 Elsevier Ltd. All rights reserved.
REVASCULARIZATION
vessel disease (usually including the LAD) and can also be used as part of a hybrid procedure in which patients undergo complete revascularization using a combination of this minimally invasive surgical procedure and percutaneous coronary intervention.
cases which are resistant to medical therapy or associated with haemodynamic compromise. Renal failure requiring temporary post-operative renal replacement therapy affects 1e5% of patients and is associated with increased mortality and morbidity. Causes include hypoperfusion, microembolism and a systemic inflammatory response syndrome. Wound infections are usually superficial but may involve the whole sternum and cause mediastinitis in 1% of patients. Risk factors include advanced age, diabetes mellitus, corticosteroid use, high body mass index, bilateral internal mammary artery grafting and need for re-exploration. Treatment depends on the condition of the patient and extent of infection. Antibiotic therapy may be sufficient for superficial infection but surgical debridement and reconstruction may be necessary for deep infection.
Robotic surgery Advances in surgical technique and technology have led to the use of robotic devices to achieve coronary revascularization with reduction in the morbidity associated with surgical trauma. The techniques are still in development and available to only a small proportion of surgical candidates at specialized centres. However, their use is likely to increase with greater experience and wider availability. Re-do CABG Re-do surgery is associated with a significant mortality and morbidity, and is technically more Principal benefits are the reduction of symptoms, alternatives such as percutaneous intervention exhausted before re-do surgery is considered.
increase in challenging. but feasible should be
Summary CABG is a safe and effective procedure which relieves the symptoms of angina and improves survival in patients with left main stem or three-vessel coronary artery disease. These benefits are further increased in those with impaired left ventricular function. Although the place of CABG has been recently challenged by percutaneous coronary intervention, recent trials demonstrate that surgical revascularization remains the gold standard in patients with complex coronary artery disease.7 Continued improvements in cardiac surgical outcomes will make coronary surgery even safer for future generations. A
Complications Mortality Peri-operative mortality is currently <2% and this figure has remained stable in recent years despite an increasingly older and sicker patient population. Contributory factors include improved surgical and anaesthetic techniques, better peri-operative medical management, and the monitoring and public reporting of surgical performance. Survival outcome for all 114,300 CABG operations performed in the UK over the 5-year period 2004e2008 has been recently published (www.scts.org). Overall hospital mortality was 1.8%, but higher (2.6%) in the 33,000 (30%) urgent patients than the 78,000 (70%) elective patients (1.1%). Similarly, 5-year survival in the two subgroups was 85% and 90%, respectively. Mortality rates were also higher in patients with diabetes mellitus (1 month 2.6%, 5-year survival 85%) and those with left main stem disease (1 month 2.5%, 5-year survival 86%).
REFERENCES 1 Yusuf S, Zucker D, Peduzzi P, et al. Effect of coronary artery bypass graft surgery on survival: overview of 10-year results from randomised trials by the Coronary Artery Bypass Graft Surgery Trialists Collaboration. Lancet 1994; 344: 563e70. 2 Eagle KA, Guyton RA, Davidoff R, et al. ACC/AHA 2004 guideline update for coronary artery bypass graft surgery: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Committee to Update the 1999 Guidelines for Coronary Artery Bypass Graft Surgery). Circulation 2004; 110: e340e437. 3 Loop FD, Lytle BW, Cosgrove DM, et al. Influence of the internalmammary-artery graft on 10-year survival and other cardiac events. N Engl J Med 1986; 314: 1e6. 4 Taggart DP, D’Amico R, Altman DG. Effect of arterial revascularisation on survival: a systematic review of studies comparing bilateral and single internal mammary arteries. Lancet 2001; 358: 870e5. 5 Taggart DP, Lees B, Gray A, Altman DG, Flather M, Channon K. Protocol for the Arterial Revascularisation Trial (ART). A randomised trial to compare survival following bilateral versus single internal mammary grafting in coronary revascularisation [ISRCTN46552265]. Trials 2006; 7: 7. 6 Abu-Omar Y, Taggart DP. The present status of off-pump coronary artery bypass grafting. Eur J Cardiothorac Surg 2009; 36: 312e21. 7 Serruys PW, Morice MC, Kappetein AP, et al. Percutaneous coronary intervention versus coronary-artery bypass grafting for severe coronary artery disease. N Engl J Med 2009; 360: 961e72.
Morbidity Cardiac surgery using CPB is associated with disturbed haemostasis and platelet function which may lead to post-operative bleeding. Around 1e2% of patients require surgical re-exploration for persistent bleeding, pericardial collection or tamponade. Stroke affects around 1% of patients e associated risk factors include advanced age, hypertension, diabetes mellitus and a previous history of stroke. More subtle cerebral injury in the form of confusion or cognitive impairment affects a third of patients early after surgery. Myocardial injury occurs to a variable extent and cardiac enzyme release can be identified in the majority of patients following cardioplegic arrest. However, lower levels observed using off-pump techniques do not necessarily translate directly into improved measures of clinical outcome. Atrial fibrillation (AF) affects one third of patients in the postoperative period with a peak incidence at 2e3 days. Treatment involves correction of serum electrolytes, appropriate antiarrhythmic medication and anticoagulation. Most cases resolve spontaneously but DC cardioversion should be considered in
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