coronary artery bypass graft

**Definition:** Open-heart (or less commonly off-pump/minimally invasive) surgery in which a conduit is anastomosed from the aorta (or another arterial source) to a coronary artery distal to an atherosclerotic stenosis, restoring perfusion to ischemic myocardium.

**Conduits (high-yield):** - **Left internal mammary (thoracic) artery (LIMA/LITA) to LAD**: gold standard. Patency ~90-95% at 10 years. It resists atherosclerosis (in part due to high nitric oxide production, and the artery usually stays attached at its origin from the subclavian). Associated with a mortality benefit. - **Saphenous vein graft (SVG)**: most commonly used additional conduit. Patency about 50-60% at 10 years. Failure is due to thrombosis (early, under 1 month), intimal hyperplasia (1 month to 1 year), and accelerated atherosclerosis (after 1 year). - **Radial artery**: an alternative arterial graft with better patency than SVG. Check collateral hand circulation first (Allen test) and avoid vasospasm (calcium channel blocker or nitrate). - **Right gastroepiploic artery**: less commonly used.

**Indications (vs. PCI or medical therapy):** - Left main disease (greater than 50% stenosis) - Three-vessel disease, especially with **diabetes** (CABG is superior to PCI, as in the FREEDOM trial) - Two-vessel disease involving the proximal LAD with reduced EF - Reduced LV function (EF under 35-50%) with multivessel disease - Failed PCI, or anatomy unsuitable for PCI (e.g., complex or chronic total occlusion lesions) - Ongoing ischemia with mechanical complications of MI requiring surgery - SYNTAX score helps guide CABG vs. PCI (high score favors CABG)

**Procedure:** Median sternotomy, then cardiopulmonary bypass (on-pump) with cardioplegic arrest. Off-pump CABG (OPCAB) avoids bypass and aortic cross-clamping, which may reduce stroke risk in selected patients. Minimally invasive direct CABG (MIDCAB) is possible for isolated LAD disease.

**Complications:** - Perioperative MI, arrhythmias (**postoperative atrial fibrillation** is the most common, peaking days 2-3) - Stroke or cognitive changes ("pump head"), related to emboli or hypoperfusion - Sternal wound infection and mediastinitis (higher risk with diabetes, obesity, and bilateral IMA use) - Bleeding and tamponade (suspect with hypotension, elevated JVP, and equalization of pressures) - Acute kidney injury - **Post-pericardiotomy syndrome** (Dressler-like, weeks after surgery: fever, pleuritic chest pain, pericardial effusion) - Graft failure and recurrent angina - Phrenic nerve injury, or saphenous harvest site complications

**Postoperative management:** Aspirin started within 6 hours to 24 hours after surgery and continued lifelong (improves graft patency). Also high-intensity statin, beta-blocker, risk-factor modification, and cardiac rehabilitation.

**Key associations/exam pearls:** - Mortality benefit: left main disease, three-vessel disease, diabetics with multivessel disease, and reduced EF. - PCI vs. CABG: PCI is preferred for single-vessel disease or high surgical risk, and CABG gives lower repeat revascularization rates. - Coronary steal and subclavian steal: a proximal subclavian stenosis can cause LIMA graft flow reversal, leading to **coronary-subclavian steal** (angina with arm exercise, with a blood pressure difference between arms). - Chest pain after CABG with elevated troponin suggests graft occlusion. Re-evaluate with angiography.