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Coronary Artery Bypass Grafting (CABG)
Definition
CABG is a surgical procedure that restores myocardial blood flow by creating new conduits (bypasses) around obstructed coronary arteries. The obstructed segment is not removed - instead, blood is rerouted past it. It is one of the most commonly performed cardiac operations worldwide.
Background & Historical Context
Before the 1950s, surgeons attempted to treat coronary artery disease (CAD) by creating pericardial or omental adhesions to the myocardium, with limited success. From the 1960s onward, the value of aortocoronary saphenous vein grafts and the internal mammary (internal thoracic) artery were increasingly recognized. By the 1970s, multiple large, prospective randomized multicenter trials confirmed improved survival in certain patient subsets after CABG. With the advent of PCI in the 1980s, the CABG population shifted toward sicker, higher-risk patients - but those with the most to gain. Multiple randomized trials comparing CABG with drug-eluting stent PCI have confirmed that CABG remains the gold standard for specific patient groups. - Bailey & Love's Surgery, p. 968
Coronary Anatomy Relevant to CABG
The coronary circulation arises from two ostia in the sinuses of Valsalva:
- Left Main Coronary Artery (LMCA) - arises from the left posterior sinus, courses between the left atrium and pulmonary trunk, then divides into:
- Left Anterior Descending (LAD) - runs along the interventricular septum; the most frequently diseased and most often bypassed artery. Supplies the LV free wall and septum.
- Left Circumflex (LCx) - runs in the atrioventricular groove, giving off obtuse marginal (OM) branches toward the apex.
- Right Coronary Artery (RCA) - courses in the right atrioventricular groove, usually giving rise to the posterior descending artery (PDA) at the crux of the heart.
Coronary dominance: ~90% of people are right-dominant (PDA from RCA), ~10% left-dominant (PDA from LCx). - Bailey & Love's Surgery, p. 968; Sabiston Textbook of Surgery
Conduit Options
| Conduit | Details |
|---|---|
| Internal Mammary (Thoracic) Artery (IMA/ITA) | Preferred conduit. Left IMA to LAD is the gold-standard anastomosis. Long-term patency far superior to vein grafts. |
| Radial Artery | Second arterial option; good patency in high-grade stenoses. |
| Saphenous Vein Graft (SVG) | Most commonly used for additional targets. Occlusion rate: 10-20% in the first year, ~2%/year at 5-7 years, ~4%/year thereafter. |
Graft patency and outcomes are significantly improved by meticulous treatment of risk factors, particularly dyslipidemia. In patients with LAD obstruction, survival is better with IMA than SVG bypass. - Harrison's Principles of Internal Medicine 22E, p. 575
Surgical Approaches
1. On-Pump CABG (Conventional)
The heart is arrested with cardioplegia and the patient is placed on cardiopulmonary bypass (CPB). This allows a still, bloodless field. CPB complications include coagulopathy, air embolism, neurological dysfunction, microembolization, pulmonary injury, and systemic organ dysfunction.
2. Off-Pump CABG (OPCAB)
Surgery is performed on the beating heart without CPB, using mechanical stabilizers. Reduces some morbidity and shortens recovery in suitable patients, but has not been shown to significantly reduce neurocognitive dysfunction. - Harrison's, p. 594
3. Minimally Invasive CABG (MIDCAB)
Performed through a small thoracotomy, avoiding full sternotomy.
4. Robotic/Totally Endoscopic CABG
Emerging approach for selected patients.
5. Hybrid Coronary Surgery
Combines CABG (usually LIMA to LAD) with PCI for remaining vessels.
Indications
CABG indications are based on symptom severity, coronary anatomy, and ventricular function. The ideal candidate has refractory or disabling angina not controlled by medical therapy, with severe stenoses of two or three epicardial coronary arteries and objective evidence of ischemia. - Harrison's, p. 598
Survival benefit is established for:
- Left main coronary artery stenosis
- Three-vessel disease, or two-vessel disease with proximal LAD involvement
- Reduced LV function (EF < 35%) with multivessel disease - the survival benefit is greatest in this group
- Patients who survived sudden cardiac death or sustained VT with obstructive CAD
- Failed PCI with high-risk findings on noninvasive testing
- Multivessel disease in diabetics - CABG is superior to PCI (including drug-eluting stents) for preventing death, MI, and repeat revascularization in this group
CABG is the gold standard for: left main stem disease, three-vessel disease, diabetics, and high-risk patients. - Bailey & Love's Surgery, p. 968
Outcomes
- Operative mortality: < 1% in low-risk patients with normal LV function operated on by experienced teams
- Angina abolished or greatly reduced in ~90% of patients after complete revascularization
- Mortality risk increases with: severe LV dysfunction, advanced age (≥80 years), comorbidities, lower surgical volume
- Sex disparity: Women undergoing CABG have persistently higher perioperative morbidity and mortality than men. In one analysis of 340,080 patients (2007-2014), women were 32% more likely to die after adjustment for confounders (adjusted OR 1.32; 95% CI 1.25-1.40). Women also had significantly higher 30- and 90-day readmission rates. - Braunwald's Heart Disease
Postoperative Considerations
- Type 5 MI - CABG-associated MI defined as cardiac troponin elevation above the 99th percentile within 48 hours of surgery. - Sabiston Textbook of Surgery
- Antiplatelet therapy (aspirin) should be started postoperatively
- Cardiac rehabilitation and risk factor modification are important after CABG
- Clopidogrel should be withheld for 5 days before elective CABG due to bleeding risk. - Tintinalli's Emergency Medicine
- Guideline-directed medical therapy (statins, ACE inhibitors, beta-blockers) continues after surgery
CABG vs. PCI - Key Points
| Factor | CABG | PCI |
|---|---|---|
| Multivessel disease | Superior | Inferior |
| Diabetes with multivessel CAD | Preferred | Not preferred |
| Left main disease | Gold standard | Emerging alternative |
| Repeat revascularization rate | Lower | Higher |
| Recovery time | Longer | Shorter |
| Suitable for | Complex anatomy, high-risk | Simpler anatomy, lower risk |
CABG remains the gold standard for left main disease, three-vessel disease, and diabetic patients with multivessel CAD despite advances in drug-eluting stent technology. - Bailey & Love's Surgery, p. 968
Sources: Harrison's Principles of Internal Medicine 22E | Sabiston Textbook of Surgery | Bailey & Love's Short Practice of Surgery 28E | Braunwald's Heart Disease
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