Coronary Artery Bypass Grafting

Updated: Apr 04, 2014
  • Author: R H Bilal, MBBS, MRCS; Chief Editor: Richard A Lange, MD, MBA  more...
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Overview

Background

Coronary artery bypass grafting (CABG) is performed for patients with coronary artery disease (CAD) to improve quality of life and reduce cardiac-related mortality. CAD is the leading cause of mortality in the United States, Europe, and Australia. [7] Additionally, it is the most common cause of heart failure. [8]

CABG was introduced in the 1960s with the aim of offering symptomatic relief, improved quality of life, and increased life expectancy to patients with CAD. [9, 10] By the 1970s, CABG was found to increase survival rates in patients with multivessel disease and left main disease when compared with medical therapy. [11]

Despite these initial positive results, the European Coronary Surgery Study conducted in the 1970s indicated that the significant improvement in 5-year survival rates with CABG was not apparent in the subsequent 5 years. [12] Nonetheless, CABG became a routine operation in patients with CAD.

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Practice Essentials

Coronary artery bypass grafting (CABG) is performed for patients with coronary artery disease (CAD) to improve quality of life and reduce cardiac-related mortality.

Indications

Class I indications for CABG from the American College of Cardiology (ACC) and the American Heart Association (AHA) are as follows [1, 2] :

  • Left main coronary artery stenosis >50%
  • Stenosis of proximal LAD and proximal circumflex >70%
  • 3-vessel disease in asymptomatic patients or those with mild or stable angina
  • 3-vessel disease with proximal LAD stenosis in patients with poor left ventricular (LV) function
  • 1- or 2-vessel disease and a large area of viable myocardium in high-risk area in patients with stable angina
  • >70% proximal LAD stenosis with either ejection fraction < 50% or demonstrable ischemia on noninvasive testing

Other indications for CABG include the following:

  • Disabling angina (Class I)
  • Ongoing ischemia in the setting of a non–ST segment elevation MI that is unresponsive to medical therapy (Class I)
  • Poor left ventricular function but with viable, nonfunctioning myocardium above the anatomic defect that can be revascularized

CABG may be performed as an emergency procedure in the context of an ST-segment elevation MI (STEMI) in cases where it has not been possible to perform percutaneous coronary intervention (PCI) or where PCI has failed and there is persistent pain and ischemia threatening a significant area of myocardium despite medical therapy.

Contraindications

CABG is not considered appropriate in asymptomatic patients who are at a low risk of MI or death. Patients who will experience little benefit from coronary revascularization are also excluded.

Although advanced age is not a contraindication, CABG is less commonly performed in the elderly. Because elderly patients have a shorter life expectancy, CABG may not necessarily prolong survival. These patients are also more likely to experience perioperative complications after CABG.

Preprocedural evaluation

Before CABG, the patient’s medical history should be carefully examined for factors that might predispose to complications, such as the following:

  • Recent MI
  • Previous cardiac surgery or chest radiation
  • Conditions predisposing to bleeding
  • Renal dysfunction
  • Cerebrovascular disease including carotid bruits and TIA
  • Electrolyte disturbances that might predispose the patient to dysrhythmias
  • Infection, including urinary tract infection and dental abscesses
  • Respiratory function, including the presence of COPD or infection [3]

Routine preoperative investigations include the following [3] :

  • Full blood count (abnormalities corrected)
  • Clotting screen
  • Creatinine and electrolytes (abnormalities corrected and discussed with the anesthetist)
  • Liver function tests
  • Screening for methicillin-resistant Staphylococcus aureus
  • Chest radiography
  • ECG
  • Echocardiography or ventriculography (to assess LV function)
  • Coronary angiography (to define the extent and location of CAD)

Premedication

The aims of premedication are to minimize myocardial oxygen demands by reducing heart rate and systemic arterial pressure and to improve myocardial blood flow with vasodilators. Drugs that should be continued up to the time of surgery are as follows:

  • Beta-blockers, calcium channel blockers, and nitrates
  • Aspirin

Agents given are as follows:

  • Temazepam immediately preoperatively
  • Midazolam, a small IV dose in the operating room before arterial line insertion

Each patient should be cross-matched with 2 units of blood (for simple cases) or 6 units of blood, fresh frozen plasma, and platelets (for complex cases). [3, 4, 5] Tranexamic acid (bolus 1 g before surgical incision followed by an infusion of 400 mg/hr during surgery) may be considered to reduce postoperative mediastinal bleeding and blood product (ie, red blood cell and fresh frozen plasma) use [6]

Anesthesia

Cardiac surgery makes use of the following 2 forms of neuraxial blockade:

  • Intrathecal opioid infusion
  • Thoracic epidural anesthesia (generally a low-dose local anesthetic/opioid infusion)

Monitoring

In addition to the standard anesthetic monitoring (ECG, pulse oximetry, nasopharyngeal temperature, urine output, gas analysis), specific monitoring requirements for cardiac surgery include the following:

  • Invasive blood pressure
  • Central venous access
  • Transesophageal echocardiography (TEE)
  • Neurologic monitoring

Technique

Sites from which the conduit can be harvested include the following:

  • Saphenous vein
  • Radial artery
  • Left internal thoracic (mammary) artery (LITA)
  • Right internal thoracic (mammary) artery (RITA)
  • Right gastroepiploic artery
  • Inferior epigastric artery
  • Splenic artery

The usual incision for CABG is a midline sternotomy (see the image below), although an anterior thoracotomy for bypass of the LAD or lateral thoracotomy for marginal vessels may be used when an off-pump procedure is being performed. Cardiopulmonary bypass, cardioplegic arrest, and placement of graft follows.

Median sternotomy Median sternotomy

Alternative approaches to CABG include the following:

  • Off-pump CABG
  • Totally endoscopic CABG
  • Hybrid technique (bypass plus stenting
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Indications

CABG is performed for both symptomatic and prognostic reasons. Indications for CABG have been classified by the American College of Cardiology (ACC) and the American Heart Association (AHA) according to the level of evidence supporting the usefulness and efficacy of the procedure [1, 2] :

  • Class I - Conditions for which there is evidence and/or general agreement that a given procedure or treatment is useful and effective
  • Class II - Conditions for which there is conflicting evidence and/or a divergence of opinion about the usefulness or efficacy of a procedure or treatment
  • Class IIa - Weight of evidence or opinion is in favor of usefulness or efficacy
  • Class IIb - Usefulness or efficacy is less well established by evidence or opinion
  • Class III - Conditions for which there is evidence and/or general agreement that the procedure/treatment is not useful or effective, and in some cases it may be harmful

Indications for CABG as detailed by the ACC and the AHA [1, 2] are listed in Table 1 below.

Table 1. ACC/AHA Indications for Coronary Artery Bypass Grafting (Open Table in a new window)

Indication Asymptomatic or Mild Angina Stable Angina Unstable Angina/ NSTEMI Poor Left Ventricular Function
Left main stenosis >50% Class I Class I Class I Class I
Stenosis of proximal LAD and proximal circumflex >70% Class I Class I Class I Class I
3-vessel disease Class I Class I   Class I, with proximal LAD stenosis
2-vessel disease   Class I if there is large area of viable myocardium in high-risk area



Class IIa if there is moderate viable area and ischemia



Class IIb  
With >70% proximal LAD stenosis Class IIa Class I with either ejection fraction < 50% or demonstrable ischemia on noninvasive testing Class IIa Class I
Involving proximal LAD Class IIb      
1-vessel disease   Class I if there is large area of viable myocardium in high-risk area



Class IIa, if there is viable moderate area and ischemia



Class IIb  
With >70% proximal LAD stenosis Class IIa Class IIa Class IIa  
Involving proximal LAD Class IIb      
ACC = American College of Cardiology; AHA = American Heart Association; LAD = left anterior descending (artery); NSTEMI = non–ST-segment elevation myocardial infarction.

Other indications for CABG include the following:

  • Disabling angina (Class I)
  • Ongoing ischemia in the setting of a non-ST segment elevation myocardial infarction that is unresponsive to medical therapy (Class I)
  • Poor left ventricular function but with viable, nonfunctioning myocardium above the anatomical defect that can be revascularized

CABG may be performed as an emergency procedure in the context of an ST-segment elevation myocardial infarction (STEMI) in cases where it has not been possible to perform percutaneous coronary intervention (PCI) or where this procedure has failed and there is persistent pain and ischemia threatening a significant area of myocardium despite medical therapy.

Other indications for CABG in the setting of STEMI are ventricular septal defect related to myocardial infarction, papillary muscle rupture, free wall rupture, ventricular pseudoaneurysm, life-threatening ventricular arrhythmias, and cardiogenic shock.

Table 2 below shows the recommendations for treatment of patients with acute heart failure in the setting of acute myocardial infarction (AMI).

Table 2. Treatment Recommendations for Patients with Acute Heart Failure in Setting of Acute Myocardial Infarction (Open Table in a new window)

  Class of Recommendation level of Evidence
Patients with NSTE-ACS or STEMI and unstable hemodynamics should immediately be transferred for invasive evaluation and target vessel revascularization Class I A
Immediate reperfusion is indicated in acute heart failure with ongoing ischemia Class I B
Echocardiography should be performed to assess LV function and exclude mechanical complications Class I C
Emergency angiography and revascularization of all critically narrowed arteries by PCI/CABG as appropriate is indicated in patients in cardiogenic shock Class I B
IABP insertion is recommended in patients with hemodynamic instability (particularly those in cardiogenic shock and with mechanical complications) Class I C
Surgery for mechanical complications of AMI should be performed as soon as possible with persistent hemodynamic deterioration despite IABP Class I B
Emergency surgery after failure of PCI or fibrinolysis is indicated only in patients with persistent hemodynamic instability or life-threatening ventricular arrhythmia due to extensive ischemia (left main or severe 3-vessel disease) Class I C
If patient continues to deteriorate without adequate cardiac output to prevent end-organ failure, temporary mechanical assistance (surgical implantation of LVAD/BiVAD) should be considered Class IIa C
Routine use of percutaneous centrifugal pumps is not recommended Class III B
AMI = acute myocardial infarction; BiVAD = biventricular assist device; CABG = coronary artery bypass grafting; IABP = intra-aortic balloon pump; LV = left ventricle; LVAD = left ventricular assist device; NSTE-ACS = non–ST-segment elevation acute coronary syndrome; PCI = percutaneous coronary intervention; STEMI = ST-segment elevation myocardial infarction.

Special recommendations in patients with comorbidities are presented in the tables below.

Table 3. Specific Treatment Recommendations for Coronary Artery Disease in Patients with Mild to Moderate Chronic Kidney Disease (Open Table in a new window)

  Recommendation level of Evidence
CABG should be considered, rather than PCI, when extent of CAD justifies surgical approach, patient’s risk profile is acceptable, and life expectancy is reasonable Class IIa B
Off-pump CABG may be considered rather than on-pump CABG Class IIb B
For PCI, disease-eluting stent may be considered, rather than bare metal stent Class IIb C
CABG = coronary artery bypass grafting; CAD = coronary artery disease; PCI = percutaneous coronary intervention.

Table 4. Specific Treatment Recommendations for Coronary Artery Disease in Diabetic Patients (Open Table in a new window)

  Recommendation level of Evidence
In patients presenting with STEMI, primary PCI is preferred over fibrinolysis if it can be performed within recommended time limits Class I A
In stable patients with extensive CAD, revascularization is indicated to improve MACCE-free survival Class I A
Use of drug-eluting stent is recommended in order to reduce restenosis and repeat target vessel revascularization Class I A
In patients on metformin, renal function should be carefully monitored after coronary angiography/PCI Class I C
CABG should be considered, rather than PCI, when extent of CAD justifies surgical approach (especially multivessel disease) and patient’s risk profile is acceptable Class IIa B
In patients with known renal failure undergoing PCI, metformin may be stopped 48 hours before procedure Class IIb C
Systematic use of glucose insulin potassium in diabetic patients undergoing revascularization is not indicated Class III B
CABG = coronary artery bypass grafting; CAD = coronary artery disease; GIK = glucose insulin potassium; MACCE = major adverse cardiac and cerebral event; PCI = percutaneous coronary intervention; STEMI = ST-segment elevation myocardial infarction.

Table 5. Recommendations for Combining Valve Surgery and Coronary Artery Bypass Grafting (Open Table in a new window)

  Recommendation level of Evidence
In combination with valve surgery:    
     
CABG is recommended in patients with primary indication for aortic/mitral valve surgery and coronary artery stenosis =70% Class I C
CABG should be considered in patients with primary indication for aortic/mitral valve surgery and coronary artery stenosis 50-70% Class IIa C
In combination with CABG:    
Mitral valve surgery is indicated in patients with primary indication for CABG and severe ischemic mitral regurgitation and EF >30% a Class I C
Mitral valve surgery should be considered in patients with primary indication for CABG and moderate ischemic mitral regurgitation, provided that valve repair is feasible and performed by experienced operators Class IIa C
Aortic valve surgery should be considered in patients with primary indication for CABG and moderate aortic stenosis (mean gradient 30-50 mm Hg, Doppler velocity 3-4 m/sec, or heavily calcified aortic valve even with Doppler velocity 2.5-3 m/sec) Class IIa C
a Definition of severe mitral regurgitation is at http://www.escardio.org/guidelines.



CABG = coronary artery bypass grafting; EF = ejection fraction.



Table 6. Carotid Revascularization in Patients Scheduled for Coronary Artery Bypass Grafting (Open Table in a new window)

  Recommendation level of Evidence
CEA or CAS should be performed only by teams with demonstrated 30-day combined death-stroke rates of < 3% in patients without previous neurologic symptoms and < 6% in patients with previous neurologic symptoms Class I A
Indication for carotid revascularization should be individualized after discussion by multidisciplinary team, including neurologist Class I C
Timing of procedures (synchronous or staged) should be dictated by local expertise and clinical presentation, with most symptomatic territory targeted first Class I C
In patients with previous TIA/nondisabling stroke:
Carotid revascularization is recommended for 70-99% carotid stenosis Class I C
Carotid revascularization may be considered for 50-69% carotid stenosis in men with symptoms < 6 months Class IIb C
Carotid revascularization is not recommended if carotid stenosis < 50% in men and < 70% in women Class III C
In patients with no previous TIA/stroke:
Carotid revascularization may be considered in men with bilateral 70-99% carotid stenosis or 70-99% carotid stenosis and contralateral occlusion Class IIb C
Carotid revascularization is not recommended in women or patients with life expectancy < 5 years Class III C
CAS = carotid artery stenting; CEA = carotid endarterectomy; TIA = transient ischemic attack.

Table 7. Management of Patients with Associated Coronary and Peripheral Arterial Disease (Open Table in a new window)

  Recommendation level of Evidence
In patients with unstable CAD, vascular surgery is postponed and CAD treated first, except when vascular surgery cannot be delayed because of life-threatening condition Class I B
Beta-blockers and statins are indicated preoperatively and continued postoperatively in patients with known CAD who are scheduled for high-risk vascular surgery. Class I B
Choice between CABG and PCI should be individualized and assessed by heart team in light of patterns of CAD, PAD, comorbidity, and clinical presentation Class I C
Prophylactic myocardial revascularization before high-risk vascular surgery may be considered in stable patients if they have persistent signs of extensive ischemic or high cardiac risk Class IIb B
CABG = coronary artery bypass grafting; CAD = coronary artery disease; PAD = peripheral arterial disease; PCI = percutaneous coronary intervention.

Table 8. Management of Patients with Renal Artery Stenosis (Open Table in a new window)

  Recommendation level of Evidence
Functional assessment of renal artery stenosis severity using pressure gradient measurements may be useful in selecting hypertensive patients who benefit from renal artery stenting Class IIb B
Routine renal artery stenting to prevent deterioration of renal function is not recommended Class III B

Table 9. Recommendations for Patients with Chronic Heart Failure and Systolic Left Ventricular Dysfunction (Ejection Fraction =35%), Presenting Predominantly with Angina Symptoms (Open Table in a new window)

  Recommendation level of Evidence
CABG is recommended for the following:
  • Significant left main stenosis
  • Left main equivalent (proximal stenosis of both left anterior descending and left circumflex)
  • Proximal left anterior descending stenosis with 2- or 3-vessel disease
Class I B
CABG with surgical ventricular reconstruction may be considered in patients with LVESV index =60 mL/m2 and scarred left anterior descending territory Class IIb B
PCI may be considered in presence of viable myocardium if anatomy is suitable Class IIb C
CABG = coronary artery bypass grafting; LVESV= left ventricular end-systolic volume; PCI = percutaneous coronary intervention.

Table 10. Recommendations for Patients with Chronic Heart Failure and Systolic Left Ventricular Dysfunction (Ejection Fraction = 35%), Presenting Predominantly with Heart Failure Symptoms (No or Mild Angina: Canadian Cardiovascular Society 1-2) (Open Table in a new window)

  Recommendation level of Evidence
LV aneurysmectomy during CABG is indicated in patients with large LV aneurysm Class I C
CABG should be considered in presence of viable myocardium, irrespective of LVESV Class IIa B
CABG with SVR may be considered in patients with scarred LAD territory Class IIb B
PCI may be considered in presence of viable myocardium if anatomy is suitable Class IIb C
Revascularization in absence of evidence of myocardial viability is not recommended Class III B
CABG = coronary artery bypass grafting; LAD = left anterior descending (artery); LV = left ventricle; LVESV = left ventricular end-systolic volume; PCI = percutaneous coronary intervention; SVR = surgical ventricular reconstruction.
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Contraindications

CABG carries a risk of morbidity and mortality and is therefore not considered appropriate in asymptomatic patients who are at a low risk of myocardial infarction or death. Patients who will experience little benefit from coronary revascularization are also excluded.

CABG is performed in elderly patients for symptomatic relief. However, although age is not a contraindication, CABG is less commonly performed in this group of patients. Because elderly patients have a shorter life expectancy, CABG may not necessarily prolong survival. These patients are also more likely to experience perioperative complications after CABG.

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Technical Considerations

Best practices

Either veins or arteries may be used as conduits for CABG. The great and small saphenous veins are the most commonly used vein grafts, and the internal thoracic (mammary) artery is the most commonly used artery.

The disadvantage of saphenous vein grafts is their declining patency with time: 10-20% are occluded 1 year after surgery because of technical errors, thrombosis, and intimal hyperplasia. Another 1-2% of vein grafts occlude every year from 1-5 years after surgery, and 4-5% occlude every year from 6-10 years after surgery. Vein graft occlusion that occurs 1 or more years after CABG is due to vein graft atherosclerosis. At 10 years after surgery, only 50-60% of saphenous vein grafts are patent, and only half of these are free of angiographic atherosclerosis.

Unlike saphenous vein grafts, internal thoracic artery grafts exhibit stable patency over time. At 10 years, more than 90% of internal thoracic artery grafts are patent. The left internal thoracic artery should be the conduit used when the left anterior coronary artery is bypassed.

Technical recommendations for CABG are presented in Table 11 below.

Table 11. Technical Recommendations for Coronary Artery Bypass Grafting (Open Table in a new window)

  Recommendation level of Evidence
Procedures should be performed in hospital structure and by team specialized in cardiac surgery, using written protocols Class I B
Arterial grafting to LAD system is indicated Class I A
Complete revascularization with arterial grafting to non-LAD coronary system is indicated in patients with reasonable life expectancy Class I A
Minimization of aortic manipulation is recommended Class I C
Graft evaluation is recommended before departure from operating theater Class I C
LAD = left anterior descending (artery).

Procedure planning

The formation of a heart team enables a balanced multidisciplinary decision-making process (see Table 12 below). The informed consent process should be seen as an opportunity to enhance objective decision-making rather than solely as a legal requirement. It is vital to be aware that factors such as sex, race, availability, technical skills, local results, referral patterns, and patient preference may affect the decision-making process independent of clinical findings.

Table 12. Multidisciplinary Decision Pathways, Patient Informed Consent, and Timing of Intervention (Open Table in a new window)

  Acute Coronary Syndrome Stable Multivessel Disease Stable with Indication for Ad-Hoc PCI
  Shock STEMI NSTE-ACS Other ACS
Multidisciplinary decision making Not mandatory Not mandatory Not required for culprit lesion but required for nonculprit vessel(s) Required Required According to predefined protocols
Informed consent Oral witnessed informed consent or family consent if possible without delay Oral witnessed informed consent may be sufficient unless written consent is legally required Written informed consenta (if time permits) Written informed consenta Written informed consenta Written informed consenta
Time to revascularization Emergency: No delay Emergency: No delay Urgency: Within 24 h if possible and no later than 72 h Urgency: Time constraints apply Elective: No time constraints Elective: No time constraints
Procedure Proceed with intervention on basis of best evidence/ availability Proceed with intervention on basis of best evidence/availability Proceed with intervention on basis of best evidence/ availability; nonculprit lesions treated according to institutional protocol Proceed with intervention on basis of best evidence/ availability; nonculprit lesions treated according to institutional protocol Plan most appropriate intervention, allowing enough time from diagnostic catheterization to intervention Proceed with intervention according to institutional protocol defined by local heart team
a May not apply to countries that legally do not ask for written informed consent, although European Society of Cardiology and European Association for Cardiothoracic Surgery strongly advocate documentation of patient consent for all revascularization procedures.



ACS = acute coronary syndrome; NSTE-ACS = non–ST-segment elevation acute coronary syndrome; PCI = percutaneous coronary intervention; STEMI = ST-segment elevation myocardial infarction.



Additional input from general practitioners, anesthesiologists, geriatricians, and intensivists may be needed.

Hospitals without a surgical cardiac unit or with interventional cardiologists working in an ambulatory setting should refer to standard evidence-based protocols devised in collaboration with expert intervention cardiologists or cardiac surgeons or should seek the opinions of these physicians for complex cases. Consensus on the best revascularization treatment should be documented. Standard protocols that are in accordance with current guidelines may be used to obviate individual case review of each diagnostic angiogram.

Ad-hoc PCI is a therapeutic interventional procedure that is performed directly after the diagnostic procedure rather than during a different session. Although it is convenient and often cost-effective, it is not desirable for all cases; some patients may be in categories for which CABG is the most suitable choice. The anatomic criteria and clinical factors that determine whether a patient can or cannot be treated by means of ad-hoc PCI should be defined by institutional protocols designed by the heart team.

Complication prevention

Cerebrovascular complications are a major cause of morbidity after CABG. The main causes of these complications are hypoperfusion or embolic events. Accordingly, it is important to maintain adequate mean arterial pressures as a prophylactic measure against hypoperfusion, although there is little that can be done to protect the patient from embolic events.

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Outcomes

In a meta-analysis of 8 randomized studies that included a total of 3612 adult patients with diabetes and multivessel CAD, treatment with CABG significantly reduced the risk of all-cause mortality by 33% at 5 years, as compared with PCI. This relative risk reduction did not differ significantly when patients who underwent CABG were compared with subgroups of patients who received either bare metal stents or drug-eluting stents. [13, 14]

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