Principle of coronary artery bypass grafting
Coronary artery bypass grafting (CABG) creates an alternative blood flow pathway in cases of critical narrowing or occlusion of a coronary artery. One end of the bypass graft is sutured to the aorta, and the other to the coronary artery distal to the lesion, allowing blood to reach the ischemic myocardium while bypassing the obstructed segment.
Main indications for surgery:
- Three-vessel disease of the coronary bed with critical stenosis;
- Critical left main coronary artery stenosis, as its severe lesion can lead to acute failure of a significant myocardial mass during physical exertion or stress.
The anastomosis between the graft and the aorta, as well as between the graft and the coronary artery, is formed in an end-to-side fashion. An end-to-end anastomosis is used less frequently, primarily for graft extension. The parachute suturing technique is most commonly used, which reduces the risk of piercing the posterior wall of the coronary artery and narrowing the anastomotic zone; the alternative anchoring technique with interrupted knots is rarely used, mainly in microscopic surgery.
Types of bypass conduits
A conduit (graft, autologous transplant) is a vessel used to create a bypass pathway. Main options:
- Internal thoracic artery (mammary artery) — supplies blood to the sternum, ribs, and adjacent soft tissues. This is the optimal conduit for bypass grafting of the left anterior descending artery: only the distal end is transected, while the proximal end retains its innervation and blood supply;
- Radial artery — similar in properties to the internal thoracic artery, but prone to spasm, thus requiring irrigation with nitroglycerin or papaverine. The ulnar end of the radial artery is sutured to the coronary artery due to a less pronounced muscular layer and a lower risk of spasm in the anastomotic zone, while the radial end is sutured to the aorta;
- Greater saphenous vein — harvested relatively easily, usually from the foot to the knee (sufficient for two grafts). When harvesting this vein, the distal end is sutured to the aorta and the proximal end to the coronary artery, since venous valves open in the proximal direction and must not obstruct blood flow.
In patients with obesity, insulin-dependent diabetes mellitus, and chronic lung diseases, harvesting the internal thoracic artery is associated with an increased risk of impaired sternal blood supply and non-union after sternotomy.
Choice of conduit depending on lesion localization
The choice of graft depends on the degree of stenosis and the location of the affected vessel:
- Stenosis greater than 70% in the lateral wall — internal thoracic or radial artery;
- Stenosis of 70–90% in the inferior wall — greater saphenous vein;
- Stenosis greater than 90% — radial artery (the right gastroepiploic artery is theoretically possible, but practically not used due to the risk of gastric ischemia and additional infectious risk from laparotomy).
On-pump and off-pump surgery
Bypass grafting is performed either on a stopped heart using cardiopulmonary bypass (on-pump) or on a beating heart without it (off-pump). When initiating cardiopulmonary bypass, an arterial cannula is inserted into the aorta to return blood, and a venous cannula is inserted into the venae cavae to drain it, after which the heart is exsanguinated and can be temporarily arrested.
Factors favoring the off-pump approach:
- Target vessel diameter greater than 1.25–1.5 mm without diffuse calcification;
- Severe atherosclerosis of the ascending aorta — risk of dislodging an atherosclerotic plaque during cannulation and subsequent embolism leading to stroke;
- Severe lung disease — during cardiopulmonary bypass, the lungs are temporarily non-functional, which can lead to postoperative atelectasis, low saturation, and pneumonia;
- Severe carotid artery disease — risk of cerebral hypoperfusion and ischemic stroke during cardiopulmonary bypass.
Clinical case review: choice of grafts in bilateral varicose veins
Analyzed the case of a patient with three-vessel disease and bilateral varicose veins of the lower extremities who requires three bypass grafts. The greater saphenous vein is unsuitable due to varicosities. Proposed solution:
- Left internal thoracic artery — standard first choice;
- Radial artery from the non-dominant arm (harvesting radial arteries from both arms is unacceptable — the patient must retain a functional dominant limb);
- Right internal thoracic artery — acceptable in the absence of obesity, diabetes mellitus, and COPD in the patient. If these conditions are present, harvesting both mammary arteries sharply increases the risk of sternal dehiscence due to inadequate blood supply, tissue hypoxia, and necrosis.
Small-diameter synthetic prostheses are not used due to rapid thrombosis. The lesser saphenous vein is considered an alternative conduit when the greater saphenous vein is unavailable, provided there is no varicosity in that area.
Key points
- CABG creates an alternative blood flow pathway in critical three-vessel disease or left main coronary artery stenosis.
- Graft-to-aorta and graft-to-coronary artery anastomoses are formed in an end-to-side fashion, predominantly using the parachute technique.
- The main conduits are the internal thoracic artery, radial artery, and greater saphenous vein, each with its own anatomical suturing features.
- For a venous graft, the proximal end is sutured to the coronary artery due to the direction of the valves.
- Harvesting both internal thoracic arteries in patients with obesity, diabetes, and COPD increases the risk of sternal dehiscence.
- The choice between on-pump and off-pump is determined by vessel diameter, the condition of the aorta, lungs, and carotid arteries.
- If standard conduits are unavailable, the lesser saphenous vein can serve as an alternative.
- CABG remains the gold standard for treating severe coronary artery disease in ischemic heart disease.