Principle of coronary artery bypass grafting
Coronary artery bypass grafting (CABG) is a method of creating a bypass blood flow to a myocardial area whose blood supply is impaired due to critical atherosclerotic lesion of the coronary artery (90-100% stenosis). Without restoring blood flow in the distal segment, myocardial infarction develops. The graft forms a new pathway for blood, bypassing the occluded vessel segment.
Classical On-Pump Technique
Classical coronary artery bypass grafting on cardiopulmonary bypass (CPB) with a stopped heart is considered the gold standard for surgical treatment of CAD.
- Single aortic cross-clamping is preferable to double clamping when constructing proximal anastomoses — this reduces the risk of atheroembolism due to trauma to the inner lining of the aorta from repeated manipulations.
- With single clamping, the distal anastomosis is constructed first, then the clamp is removed, the heart is restarted, and the proximal anastomoses (connections between the graft and the aorta) are sutured on a partially clamped aorta.
- The mortality rate for CABG on CPB is 1-3%.
- Main complications: stroke, renal dysfunction (due to renal hypoperfusion during CPB), deep sternal wound infection after sternotomy with possible wound dehiscence, atrial fibrillation (up to 24% of cases — one of the most frequent complications).
- Postoperatively, patients take aspirin at a dose of 80-325 mg.
The use of cardioplegia on a arrested heart improves surgical field visualization and facilitates sequential anastomosis construction since the heart is bloodless and motionless.
Indications for Coronary Artery Bypass Grafting
Level of evidence 1a:
- Critical left main coronary artery disease (from which the left anterior descending and circumflex arteries originate, supplying virtually the entire heart).
- Three-vessel disease.
- Two-vessel disease combined with critical stenosis of the proximal left anterior descending artery.
Level of evidence 2a:
- Critical two-vessel disease without involvement of the proximal left anterior descending artery, but with severe ischemia.
- Critical stenosis of the proximal left anterior descending artery combined with left ventricular dysfunction (ejection fraction 30-50%).
Types of Vascular Conduits (Grafts)
Three main types of conduits are used for bypass grafting.
- Internal thoracic artery (internal mammary artery) is the gold standard of choice. It originates from the subclavian artery; during harvest, only the distal segment is transected, while the proximal segment remains in the bloodstream, preserving its innervation. The endothelium of the preserved vessel produces nitric oxide, providing arterial dilation during increased myocardial oxygen demand. The wall structure prevents the development of atherosclerosis. Most frequently sutured to the left anterior descending artery due to topological similarity. Patency is 90% at 20 years.
- Radial artery — harvested from the nondominant arm after confirming the ulnar artery's ability to adequately supply the hand (radial and ulnar arteries form the palmar arch). The Allen test and modified Allen test with oxygen saturation waveform monitoring are used. Before harvesting, it is essential to rule out arterial calcification. The distal segment is sutured to a coronary artery with a less prominent muscular layer to reduce the risk of spasm; nitrates and calcium channel blockers are additionally used. Patency is 84% at 20 years.
- Greater saphenous vein — the most commonly used conduit. The classical harvest method involves skeletonization of the vessel without surrounding tissue via a leg incision. Patency is about 80% at 10 years; results depend on harvesting technique, quality of anastomoses, and patient compliance (medication intake, smoking cessation).
The gastroepiploic (right gastroepiploic) artery was also previously used, but is currently practically obsolete.
Off-Pump Coronary Artery Bypass (OPCAB)
Off-pump technology — construction of bypass grafts without cardiopulmonary bypass, on a beating heart. Historically the first CABG technique, it is currently a well-studied, routinely applied method. The coronary artery segment is stabilized using a specialized myocardial stabilizer ("octopus").
- Pros of off-pump: absence of CPB-related complications (stroke, aortic dissection, atrial fibrillation); rapid patient recovery (discharge on days 5-7).
- Cons of off-pump: unstable hemodynamics during beating-heart manipulations with the risk of blood pressure drop and the need to convert to CPB; technical difficulty of anastomosis construction due to bleeding from the opened artery.
- Pros of the classical on-pump technique: good visualization on a bloodless, motionless heart, technical simplicity, hemodynamic stability.
- Cons of the on-pump technique: risks of CPB complications (dissection, stroke, renal failure), longer recovery period.
The choice of technique depends on the condition of the coronary vessels (diffuse disease, calcification, need for endarterectomy), the location of the target artery (deeply intramyocardial), as well as patient comorbidities: advanced age, severe aortic atherosclerosis, severe chronic obstructive pulmonary disease. In the presence of these factors, off-pump surgery is preferred; in their absence, the classical on-pump technique is chosen. The surgeon's experience plays an important role.
Success Factors and the Role of the Method in CAD Treatment
Long-term success of coronary artery bypass grafting depends on graft quality (vein or artery), patient adherence to secondary prevention, pharmacotherapy prescribed by cardiologists and surgeons, and postoperative lifestyle modifications: physical therapy, regular walking, balanced nutrition, smoking and alcohol cessation, and stress reduction.
Coronary artery bypass grafting remains the gold standard for CAD treatment when appropriate indications are present. Numerous studies confirm that in critical three-vessel disease, bypass surgery is the method of choice rather than stenting.
Key points
- Coronary artery bypass grafting creates a bypass blood flow around a critically stenosed segment of the coronary artery.
- The classical on-pump technique with single aortic cross-clamping is the gold standard, reducing the risk of atheroembolism.
- Class 1a indications: left main disease, three-vessel disease, two-vessel disease with critical proximal left anterior descending stenosis.
- The internal thoracic artery is the best conduit with 90% patency at 20 years due to preservation of blood flow and innervation.
- The radial artery requires preliminary verification of adequate hand blood supply by the ulnar artery (Allen test).
- Off-pump surgery reduces CPB-related risks, but is technically more challenging and less hemodynamically stable.
- Method selection depends on vascular status, lesion location, patient age, and surgeon experience.
- In critical three-vessel disease, bypass surgery remains the method of choice rather than stenting.