What are the risks associated with Coronary Artery Bypass Grafting (CABG)?

Risks of Coronary Artery Bypass Grafting (CABG)

CABG carries an overall operative mortality of 1-4% in contemporary practice, with significantly higher risks in specific patient populations including those requiring reoperation (3-fold increased mortality), patients with severe left ventricular dysfunction, and those with multiple comorbidities. 1

Mortality Risk

• Overall operative mortality ranges from 1-4% depending on the patient population studied, with well-developed risk stratification models available (such as STS score) to assess individual patient risk 1
• Reoperation after previous CABG increases mortality risk approximately 3-fold compared to primary operations 1
• Emergency CABG for failed percutaneous coronary intervention carries substantially higher mortality and myocardial infarction rates compared to elective surgery 1
• Patients with insulin-treated diabetes have significantly increased risk of major adverse events (adjusted odds ratio 1.49) compared to non-diabetic patients 2

Neurological Complications

Stroke

• Stroke occurs in approximately 1-3% of CABG patients, rising to 5% in those with bilateral carotid stenoses and 11% in those with an occluded carotid artery 1
• Stroke after CABG entails a 3-6 fold increased risk of mortality, permanent disability, and longer hospital stays 3
• The risk of stroke has not significantly declined over the past decade despite advances in surgical techniques, likely because older and sicker patients are now undergoing CABG 3
• Two major mechanisms cause perioperative stroke: cerebral embolization of atheromatous debris from the ascending aorta during surgical manipulation, and cerebral hypoperfusion during surgery 3
• Atrial fibrillation occurring postoperatively increases stroke risk and requires anticoagulation if it persists beyond 48 hours 4

Cognitive Dysfunction

• Postoperative cognitive changes can occur, though specific incidence rates vary by assessment method 1

Cardiovascular Complications

Graft Failure

• Saphenous vein graft patency: >90% at 1 year, 65-80% at 4-5 years, and only 25-50% at 10-15 years 1
• Left internal thoracic artery (LITA) patency: >91% at 1 year, 88% at 4-5 years, and 88% at 10-15 years 1
• Radial artery patency: 86-96% at 1 year, 89% at 4-5 years 1
• Early graft failure (within 36 hours) occurs in a small percentage of patients and may require urgent reintervention 1

Arrhythmias

• Atrial fibrillation is a common postoperative complication requiring rate control and consideration of anticoagulation 5
• Ventricular arrhythmias can occur, particularly in patients with pre-existing left ventricular dysfunction 5

Myocardial Infarction

• Perioperative myocardial infarction occurs in a subset of patients, with rates varying by surgical technique and patient risk factors 6
• Emergency CABG for failed angioplasty carries higher rates of subsequent MI 1

Infectious Complications

Sternal Wound Infections

• Deep sternal wound infections represent a serious complication requiring aggressive management 5
• Patients with diabetes, particularly insulin-treated diabetes, face increased risk of wound complications 2
• Wound infection rates are influenced by patient factors including obesity, diabetes, and immunosuppression 5

Pneumonia

• Postoperative pneumonia occurs more frequently in patients with chronic obstructive pulmonary disease and those requiring prolonged mechanical ventilation 5

Renal Complications

• Postoperative renal dysfunction occurs in a significant proportion of patients, with some requiring new dialysis 5, 2
• Patients with pre-existing renal insufficiency face substantially higher risk of postoperative renal failure 7
• Renal dysfunction is associated with increased mortality and prolonged hospital stays 7

Pulmonary Complications

• Prolonged mechanical ventilation is required in some patients, particularly those with pre-existing chronic obstructive pulmonary disease 2
• Pulmonary hypertension can develop or worsen postoperatively 5
• Patients with chronic obstructive pulmonary disease (present in 18.6% of contemporary CABG patients) face increased risk of respiratory complications 7

Gastrointestinal Complications

• Gastrointestinal insults can occur postoperatively, ranging from ileus to more serious complications 5
• Patients with ischemic hepatopathy face dramatically increased mortality: Child class A cirrhosis carries 11% operative mortality, Child class B has 18% mortality, and Child class C has 67% operative mortality 8

Bleeding and Hematologic Complications

• Reoperation for bleeding management is required in approximately 3% of patients 6
• Pericardial effusion can develop, with risk of cardiac tamponade if anticoagulation is initiated too aggressively 4
• Patients with impaired coagulation systems face increased risk, particularly those requiring reoperation 1

Thromboembolic Complications

• Thromboembolic phenomena can occur despite antiplatelet therapy 5
• Risk is particularly elevated in patients who develop postoperative atrial fibrillation 4

High-Risk Patient Populations

Comorbidity Burden

• In contemporary practice, 29.9% of CABG patients have diabetes mellitus, 16% have peripheral vascular disease, 18.6% have chronic obstructive pulmonary disease, and 27.5% have renal dysfunction 7
• Patients with multiple comorbidities are more likely to be elderly and female, require special care after discharge, and face increased risk of adverse outcomes 7

Diabetes

• Patients with insulin-treated diabetes represent an especially high-risk group with adjusted odds ratio of 1.49 for major adverse events compared to non-diabetic patients 2
• Non-insulin-treated diabetes also increases risk (adjusted odds ratio 1.15) but to a lesser degree 2
• Diabetic patients have higher prevalence of preoperative comorbidities and worse postoperative outcomes 2

Left Ventricular Dysfunction

• Patients with severe left ventricular dysfunction (ejection fraction <35%) face increased operative risk 1
• Right ventricular dysfunction, particularly with inferior infarction, complicates perioperative management 1

Elderly Patients

• Age ≥65 years is a risk factor for carotid artery disease and increased stroke risk 1
• Older patients are more likely to have multiple comorbidities and face higher operative mortality 7

Emergency Department Presentations

• Up to 14% of CABG patients present to the emergency department within 30 days of discharge with postoperative complications 5
• Early surgical consultation is imperative when complications are suspected, as this improves patient outcomes 5
• Critical patients require evaluation in the resuscitation bay with optimization of hemodynamics including preload, heart rate, cardiac rhythm, contractility, and afterload 5

Risk Mitigation Strategies

Surgical Technique Considerations

• Use of left internal mammary artery to the left anterior descending artery improves long-term outcomes compared to saphenous vein grafts 1
• Mechanical stabilization of the coronary artery during anastomosis increases graft patency rates (97% vs 89% for conventional techniques) 6
• Off-pump surgery may reduce perioperative morbidity in selected patients, though randomized trials show reduced graft patency (90% vs 98%) at 3-6 months 1
• Anaortic approaches (total arterial revascularization with in situ grafting) minimize stroke risk in high-risk patients by avoiding aortic manipulation 3

Preoperative Assessment

• Intraoperative ultrasound scanning of the ascending aorta has the best sensitivity and specificity for detecting atheromatous debris that increases stroke risk 3
• Carotid artery screening should be performed in patients with risk factors: age ≥65 years, carotid bruit, history of cerebrovascular disease, smoking, diabetes, hypertension, peripheral arterial disease, or left main coronary artery disease 1

Postoperative Management

• Beta-blockers must be resumed as soon as possible after CABG to reduce inflammatory response and improve cardiac output 9
• ACE inhibitors/ARBs should be initiated postoperatively in stable patients with LVEF ≤40%, hypertension, diabetes, or chronic kidney disease 9
• Maintain mean arterial pressure >60 mmHg to ensure adequate organ perfusion 9
• Aggressive treatment of postoperative atrial fibrillation reduces stroke risk; if atrial fibrillation persists >48 hours, initiate warfarin (INR 2.0-3.0) balancing against bleeding risk 4