Coronary Artery Bypass Surgery
Coronary artery bypass surgery, also known as coronary artery bypass grafting (CABG), is a major cardiac surgical procedure used to treat coronary artery disease (CAD). Coronary artery disease results from the accumulation of atheromatous plaques within the coronary arteries, leading to narrowing (stenosis) and reduced blood flow to the heart muscle. CABG aims to restore adequate myocardial perfusion by bypassing diseased arterial segments using grafts harvested from other parts of the body. The procedure is widely recognised for its effectiveness in relieving angina, improving quality of life, slowing disease progression, and increasing survival in selected patient groups.
Background and Rationale
The heart muscle requires a continuous supply of oxygenated blood delivered by the coronary circulation. When one or more coronary arteries become significantly narrowed, myocardial ischaemia develops. This may manifest as exertional chest pain (stable angina), pain at rest (unstable angina), or acute myocardial infarction if blood flow is abruptly interrupted. Early attempts to treat angina date back to the beginning of the twentieth century, but it was in the 1960s that CABG was developed in its modern form. Since then, it has become one of the cornerstone treatments for advanced coronary artery disease.
The principle underlying CABG is anatomical revascularisation. Blood flow is redirected around obstructed coronary segments by surgically attaching a graft vessel from the aorta or a major artery to a point beyond the stenosis, thereby supplying oxygenated blood to previously ischaemic myocardium.
Surgical Approaches and Techniques
There are two main surgical approaches to coronary artery bypass surgery.
The traditional method uses cardiopulmonary bypass. In this approach, a heart–lung machine temporarily takes over the functions of the heart and lungs, circulating and oxygenating blood during surgery. The heart is arrested using cardioplegia, allowing the surgeon to operate on a still, bloodless field. Harvested graft vessels are then connected to the coronary arteries beyond the blocked segments, a process known as surgical anastomosis.
The second approach is off-pump coronary artery bypass (OPCAB). In this technique, grafts are constructed while the heart continues to beat. Special stabilising devices are used to minimise movement at the site of anastomosis. OPCAB avoids the use of cardiopulmonary bypass and may reduce certain complications in selected patients, although its long-term outcomes are broadly comparable to conventional surgery in experienced centres.
The most critical graft is usually to the left anterior descending artery, which supplies a large portion of the left ventricle. The left internal mammary artery is most commonly used for this purpose due to its excellent long-term patency. Other frequently used conduits include the right internal mammary artery, the radial artery, and the great saphenous vein from the leg.
Vessel Harvesting and Graft Selection
Graft selection is a key determinant of long-term success. Arterial grafts, particularly the internal mammary arteries, have superior durability compared with venous grafts and are associated with improved survival. Venous grafts, most commonly harvested from the great saphenous vein, remain widely used because of their length, ease of harvesting, and versatility.
Harvesting techniques have evolved to reduce complications. Minimally invasive and endoscopic methods are increasingly employed to reduce wound infection, pain, and recovery time, particularly for leg vein harvesting.
Indications for Coronary Artery Bypass Surgery
CABG is indicated when coronary artery disease is sufficiently severe that medical therapy or percutaneous coronary intervention (PCI) is unlikely to provide durable benefit.
In stable patients, angina is initially managed with medications. Non-invasive investigations such as exercise electrocardiography, echocardiography, and imaging-based stress tests help identify patients with significant myocardial ischaemia. Coronary angiography is performed to define coronary anatomy and lesion severity. CABG is generally preferred over PCI in patients with extensive and complex coronary disease, left main coronary artery stenosis, impaired left ventricular function, diabetes mellitus, or triple-vessel disease, particularly when the proximal left anterior descending artery is involved.
In acute coronary syndrome, rapid restoration of blood flow is critical. Most patients are initially managed with antiplatelet therapy and PCI. Urgent CABG is indicated when PCI fails, when anatomy is unsuitable for catheter-based intervention, or when mechanical complications of myocardial infarction occur, such as ventricular septal rupture, papillary muscle rupture, or myocardial free wall rupture. Timing of surgery influences outcomes, with delayed intervention preferred when feasible to reduce operative risk.
CABG is also performed in conjunction with other cardiac surgery, most commonly valve repair or replacement, when significant coronary lesions are identified during preoperative assessment.
Diagnosis and Assessment of Coronary Artery Disease
Accurate diagnosis and assessment of coronary artery disease are essential in determining the appropriateness of CABG. Non-invasive methods include resting and exercise electrocardiography, chest radiography, and echocardiography. Echocardiography provides valuable information on ventricular function, chamber size, valve structure, and ejection fraction.
The most definitive diagnostic tools are coronary angiography and coronary computed tomography angiography. These modalities visualise the coronary arteries directly and identify the location and severity of stenotic lesions. Lesion significance is often assessed by percentage diameter reduction, with severe stenosis typically defined as a reduction exceeding two-thirds of the arterial diameter. Adjunctive techniques such as intravascular ultrasound and fractional flow reserve measurement provide further physiological and structural information.
CABG Versus Percutaneous Coronary Intervention
CABG and PCI are the two principal methods of revascularisation for coronary artery disease. While PCI is less invasive and associated with shorter recovery times, CABG offers superior long-term outcomes in specific patient populations.
Strong evidence supports CABG over PCI in patients with left main coronary artery disease, multivessel disease, diabetes mellitus, and impaired left ventricular function. The protective effect of arterial grafts, which secrete vasodilatory factors and resist atherosclerosis, contributes to improved durability. Multiple large trials and long-term follow-up studies have demonstrated lower mortality and fewer adverse cardiac events with CABG compared with PCI in these high-risk groups.
Complications and Risks
Coronary artery bypass surgery is a major operation and carries significant risks. Common complications include bleeding, myocardial infarction, arrhythmias, stroke, infection, pneumonia, and acute kidney failure. Neurological complications and wound infections are of particular concern in elderly patients and those with multiple comorbidities.
Despite these risks, advances in surgical technique, anaesthesia, and perioperative care have significantly improved safety and outcomes. Careful patient selection and optimisation remain essential.
