Coronary Artery Bypass Grafting (CABG) - Detailed Notes from the PDF

1. Epidemiology and Background

• Overall cardiovascular disease death rates have declined by 31%; CAD deaths fell by 39.2%.
• CABG remains the dominant surgical approach for multivessel CAD, especially in patients with left main disease, three-vessel disease with LV dysfunction, or complex disease where PCI has limited durability.
• The STS database reports perioperative mortality of 1-2% for isolated CABG, making short-term mortality an increasingly insensitive quality marker; attention has shifted toward long-term mortality, readmission rates, and neurocognitive outcomes.

2. Indications and Surgical Decision-Making

• Guideline support: ACC/AHA guidelines emphasize the efficacy of CABG over PCI for multivessel CAD - particularly three-vessel disease or left main involvement.
• SYNTAX Trial: 5-year follow-up confirmed a survival advantage for CABG over PCI in patients with intermediate to high anatomic complexity (SYNTAX score), with the advantage increasing with longer follow-up.
• Heart team approach: The decision to proceed to CABG requires close collaboration between cardiac surgery, interventional cardiology, and anesthesia.
• Significant valvular abnormalities (especially ischemic mitral regurgitation) should be evaluated and incorporated into surgical planning.

3. Coronary Anatomy Relevant to CABG

• Atherosclerosis preferentially occurs at bifurcations where blood flow is slower and shear stress is low, stimulating an atherogenic endothelial phenotype.
• Combined stenosis of the RCA and both branches of the left coronary artery = triple-vessel disease.
• Common distal anastomosis targets:
  • Left anterior descending (LAD) and its diagonals
  • Obtuse marginal branches of the circumflex
  • Posterior descending artery (PDA) - from RCA in right-dominant anatomy
  • Acute marginal branches
• Venous drainage is primarily via the coronary sinus into the right atrium; a small fraction via Thebesian veins directly into cardiac chambers.

4. Pathophysiology of Ischemia Relevant to CABG

• Ischemia results when myocardial O2 demand exceeds the capacity of stenosed coronaries to increase supply.
• An atherosclerotic lesion creates a pressure gradient and reduces distal coronary perfusion pressure (CPP).
• In high-grade stenosis, the distal microvasculature may already be maximally dilated at rest, leaving no autoregulatory reserve.
• Collateral vessels develop between ischemic and non-ischemic zones - patients with severe, chronic stenosis often have extensive collaterals that protect against infarction. Notably, the culprit vessel in acute MI is often only moderately stenosed - plaque rupture and thrombosis, not the degree of stenosis, determine infarction size.

5. Preoperative Risk Assessment

• Elevated mean PAP before CPB (>30 mmHg; OR = 2.1)
• Low MAP during CPB (40-49 mmHg; OR = 1.3)
• Tachycardia (HR >120 bpm; OR = 3.1)
• High diastolic PAP after CPB (>20 mmHg; OR = 1.2)
• (Plus two others - inotrope support was required in 39% of the cohort)

6. Preoperative Medication Management

1. Beta-blockers - Administer ≥24 hours before CABG to all patients without contraindications (hypotension, 3rd-degree AV block, bronchospasm). Reinstitute ASAP postoperatively.
2. Statins - All CABG patients should receive them unless contraindicated.
3. Calcium channel blockers - Continue perioperatively if the patient is already on them.
4. ACE inhibitors/ARBs - Preoperative discontinuation is controversial (risk of hypotension/vasoplegic syndrome). Post-CABG, initiate and continue indefinitely in patients with LV dysfunction.
5. Diuretics - No firm recommendations; ensure adequate serum potassium.
6. Aspirin - Give preoperatively. Restart within 6-24 hours postoperatively.
7. P2Y12 inhibitors (clopidogrel, etc.) - Hold 5 days before surgery due to bleeding risk. Exception: high-risk patients or drug-eluting stent recipients may continue with IV GpIIb/IIIa inhibitors or cangrelor as bridging.
8. Heparin - Discontinue 4 hours preoperatively in stable patients; continue up to pre-CPB period in critical left main disease or acutely unstable angina.
9. Oral hypoglycemics - Consider withholding; maintain strict glucose control.
10. Antibiotic prophylaxis - Cefazolin 2g IV or cefuroxime 1.5g IV, given 20-60 min before incision. Vancomycin 15 mg/kg (slow infusion, completed 20-30 min before incision to ensure tissue penetration).

7. Intraoperative Monitoring

Standard monitors (Box 20.3):

• 5-lead system is standard.
• Lead V5 - most sensitive for ischemia.
• Lead II - rhythm monitoring and inferior wall ischemia detection.
• Combined V5 + II detects ~90% of ischemic episodes.

• Radial artery cannulation is standard.
• Radial artery pressures are notoriously inaccurate immediately after hypothermic CPB (underestimates aortic pressure by significant amounts) - takes 20-60 minutes to resolve due to decreased forearm vascular resistance.
• Alternatives: femoral, axillary artery; or direct aortic pressure measurement via needle/cardioplegia cannula.

• Used for drug delivery, volume infusion.
• Inserted before induction (right internal jugular or subclavian).

• Routine use has declined; large randomized studies show no improvement in major outcomes.
• Indicated for: pulmonary hypertension, right heart failure, severely impaired ventricular function, and postoperative cardiac output monitoring.

• Recommended for ALL cardiac operations.
• Roles in CABG:
  • Pre-CPB: LV/RV function, valvular lesions (especially functional MR), aortic atheroma (guide cannulation site), PFO, persistent LSVC
  • During CPB: cannula positioning (retrograde cardioplegia, aortic cannula - detect iatrogenic dissection)
  • Post-CPB: de-airing, ventricular function, wall motion, response to inotropes

• Cerebral oximetry (NIRS-based) - continuously monitors regional brain O2 saturation even during low-flow CPB; early warning for catastrophic events not caught by pulse oximetry.
• Processed EEG - bispectral index (BIS) and similar; reduces awareness risk and can guide burst suppression during hypothermic arrest.
• ACCF/AHA 2011 guidelines: Class IIb recommendation for CNS monitoring during myocardial revascularization.

• Bladder or esophageal probe (core temperature) + nasopharyngeal or tympanic probe (brain temperature).
• Important to minimize temperature gradients and prevent cerebral hyperthermia during CPB rewarming.

8. Anesthetic Induction and Maintenance

• No single technique is universally optimal - LV function and coronary pathology guide agent selection.
• The goal in modern practice: extubate within 6 hours postoperatively (fast-tracking).
• Key focus: hemodynamic stability, avoiding ischemia (tachycardia is especially harmful), minimizing myocardial O2 demand-supply mismatch.

• Short-acting benzodiazepines (e.g., midazolam) are standard for anxiolysis/amnesia.
• Given IV in the holding area with supplemental O2 and monitoring.
• Reduces anxiety-driven tachycardia and preoperative anginal episodes.

• Most hypnotics, opioids, and volatile agents have been used in combination with good results.
• Midazolam - well tolerated with minimal hemodynamic effects even in severe cardiac dysfunction.
• Thiopental, propofol, etomidate - used per institutional preference.
• Fast-tracking: limit high-dose opioids; use short-acting drugs.

• Sufentanil: ~3 µg/kg total; hemodynamic control inflection point at plasma level ~0.71 ng/mL.
• Fentanyl: ~20 µg/kg total; inflection point at ~7.3 ng/mL.
• Supplemented with volatile agents for hemodynamic control and myocardial protection.

• Pancuronium historically paired with high-dose opioids to offset bradycardia, but causes tachycardia risk.
• Newer agents (vecuronium, cisatracurium) preferred in fast-track protocols.

9. Cardioprotection: Preconditioning and Postconditioning

• Volatile agents (sevoflurane, isoflurane, desflurane) mimic ischemic preconditioning.
• Sevoflurane + mechanical ischemic preconditioning = additive reduction in infarction size.
• Isoflurane + morphine = additive infarct-size reduction.
• OPCAB patients may benefit more than on-pump CABG patients.
• ACCF/AHA 2011 guidelines: Level A evidence for volatile-based anesthesia to reduce perioperative myocardial ischemia/infarction in revascularization.

• Diabetes mellitus
• Female sex
• Intraoperative hyperglycemia (may be reversed by N-acetylcysteine)

• Brief reperfusion-ischemia cycles at the onset of reperfusion reduce MI size.
• Volatile agents also mimic postconditioning effects and blunt reperfusion injury and the systemic inflammatory response after cardiac surgery.

10. Regional/Neuraxial Techniques

• Well-studied; thoracic sympathectomy has favorable effects on myocardial O2 balance.
• Advantages: improved analgesia, earlier extubation.
• Used in awake OPCAB: 97% success in selected series; 2-3% conversion to GA.
• Concern: catastrophic epidural hematoma risk when full heparinization for CPB is used.
• ASRA consensus: appropriate withdrawal of anticoagulants/antiplatelets before placement and before catheter removal.
• Outcome data: No significant difference in major outcomes (mortality, major morbidity) with TEA vs. GA alone in most studies; minor benefits in analgesia and time to extubation.

11. Management of Intraoperative Ischemia

• Promotes venodilation (preload reduction) and mild arteriolar dilation (afterload reduction).
• Intraoperative indications (Box 20.5): hypertension, elevated PAP, new AC/V waves (ischemic MR), ST changes >1 mm, new RWMA on TEE, diastolic/systolic dysfunction, coronary spasm.
• Post-CPB indications (Box 20.6): myocardial stunning, diastolic dysfunction, elevated PAP/PCWP/CVP/PVR/SVR, prevention of arterial graft spasm (especially radial artery grafts), reinfusion of oxygenator volume.

• Nicardipine: unique consistent augmentation of coronary blood flow; minimal myocardial depression; good for perioperative hypertension control.
  • Nicardipine 0.7-1.4 µg/kg/min vs NTG 0.5-1 µg/kg/min post-revascularization: 0% vs 10% myocardial ischemia incidence in nicardipine group.
• Clevidipine: ultrashort-acting dihydropyridine calcium channel blocker; arterial-selective; metabolized by blood/tissue esterases. ECLIPSE trial: compared with nitroprusside, clevidipine-treated patients had significantly lower mortality (P = .04).
• Nitroglycerin remains preferred over verapamil (myocardial depression, conduction block) and nifedipine (reflex tachycardia).

• Esmolol: ultrashort-acting; ideal for acute intraoperative rate control.
• Metoprolol, labetalol: for sustained beta-blockade.

12. Heparin Management for CPB

• Standard heparin dose: 300-400 IU/kg (or calculated by Hepcon heparin titration).
• Target before initiating CPB: ACT >480 seconds and/or heparin level >2.5 U/mL.
• Heparin is also given before clamping the LIMA pedicle to prevent thrombosis.
• Antifibrinolytic therapy (epsilon-aminocaproic acid or tranexamic acid) is standard in on-pump CABG (not used in OPCAB). Aprotinin is no longer available in the US.

13. On-Pump vs. Off-Pump CABG (OPCAB)

• OPCAB is an established alternative to on-pump CABG.
• Despite theoretical advantages of avoiding CPB (less inflammation, no emboli from aortic cross-clamping), large prospective trials in mostly low-risk patients have NOT shown clear mortality reductions with OPCAB.
• Outcomes are highly surgeon-dependent.
• Anesthetic considerations differ: no heparin anticoagulation for CPB, different hemodynamic management during cardiac positioning and stabilization, no antifibrinolytics.

14. Concomitant Procedures

• Mitral valve repair at the time of CABG remains controversial.
• Should be considered in patients with a dilated annulus and at least moderate ischemic MR.

15. Fast-Tracking and Postoperative Care

• Fast-tracking (early extubation within 6 hours + early mobilization) has been almost universally adopted.
• Requires:
  • Limiting high-dose long-acting opioids
  • Short-acting NMBAs
  • Volatile anesthetic-based maintenance
  • Goal: extubate in OR or within 6 hours in ICU
• Advantages: reduced ICU/hospital LOS, improved patient satisfaction, cost reduction.

Key Points Summary

1. CABG guideline-supported for multivessel CAD, especially complex anatomy (SYNTAX intermediate/high).
2. Perioperative medication management is comprehensive - beta-blockers, statins, aspirin, P2Y12 timing, glucose control all need attention.
3. Intraoperative monitoring backbone: ECG (V5+II), invasive arterial line, TEE for all cases.
4. No single anesthetic technique is superior - volatile-based anesthesia carries Level A evidence for myocardial protection.
5. Heparin to ACT >480 s before CPB; antifibrinolytics for on-pump; none for OPCAB.
6. Fast-tracking is standard; target extubation within 6 hours.
7. OPCAB avoids CPB but shows no mortality benefit in large low-risk trials.
8. Neuraxial techniques (TEA) have minor advantages in analgesia/extubation but no proven major outcome benefit, with hematoma risk requiring careful anticoagulation management.

OPCAB vs. On-Pump CABG: Outcomes and Anesthetic Considerations

1. Historical Context

2. Theoretical Basis for Choosing OPCAB

• Systemic inflammatory response syndrome (SIRS) from blood-foreign surface contact
• Hemodilution and coagulopathy
• Particulate and gaseous microemboli
• Non-pulsatile flow during bypass
• Temperature fluctuations and risk of cerebral hyperthermia during rewarming

• Embolization of aortic atheromatous debris - the primary mechanism of perioperative stroke
• Myocardial ischemia during arrest (cardioplegia-dependent protection)

3. Surgical Considerations Unique to OPCAB

Mechanical Stabilizers

• Compression-type stabilizers (Maquet, Medtronic Octopus) press against the epicardium to reduce local motion around the target vessel.
• Suction-cup systems (Medtronic Starfish apical device) lift and position the heart with less hemodynamic compromise (~6% reduction in SV with Starfish vs. ~44% reduction with compression-type devices during verticalization in animal models).

Cardiac Positioning

"Verticalization" ECG Artifact

• Heart positioning during PDA or circumflex anastomosis changes the spatial relationship between the heart and surface ECG electrodes.
• The ECG amplitude decreases markedly and can be misread by the monitor as asystole, triggering an audible alarm. The team must recognize this as a positional artifact, not true arrest.

4. Outcomes Comparison

Large Trial and Meta-Analysis Data

• No significant differences in: 30-day or 1-2-year mortality, MI, stroke (30-day or 1-2 years), renal dysfunction, IABP requirement, wound infection, reoperation for bleeding, or reintervention for ischemia
• OPCAB significantly better on:
  • Atrial fibrillation: OR = 0.58 (42% relative reduction)
  • Transfusion requirement: OR = 0.43 (57% relative reduction)
  • Respiratory infections: OR = 0.41
  • Need for inotropes: OR = 0.48
  • Duration of ventilation: -3.4 hours
  • ICU LOS: -0.3 days
  • Hospital LOS: -1.0 days
  • Neurocognitive dysfunction at 2-6 months: OR = 0.57 (improved with OPCAB)
  • No difference at 12 months for neurocognition

• 91 fewer develop AF
• 143 fewer require transfusion
• 83 fewer require inotropes
• 53 fewer develop respiratory infections
• 100 fewer have cognitive dysfunction at 2-6 months
• 300 fewer ICU days
• 1000 fewer hospital days

• OPCAB significantly reduced short-term stroke (1.27% vs 1.78%, OR=0.74, P=0.03; HIGH certainty evidence)
• OPCAB associated with increased mid-term coronary reintervention (2.77% vs 1.85%, RR=1.49, P<0.01; HIGH certainty)
• OPCAB associated with increased long-term mortality (21.8% vs 21.0%, RR=1.09, P=0.02; MODERATE certainty)

• No significant differences in mid-term mortality (HR=1.02) or composite endpoint (HR=0.98)
• No 30-day differences in mortality, MI, stroke, or renal complications
• OPCAB: higher early re-revascularization (OR=3.22, P=0.01), linked to higher rates of incomplete revascularization (34% OPCAB vs 29% on-pump)

ROOBY Trial (Shroyer et al., VA Cooperative study)

• Prospective, randomized, on-pump vs off-pump
• Found worse composite outcomes and poorer graft patency in the off-pump group
• Criticized for: minimum surgeon experience of only 20 OPCAB cases, conversion rate 12.4% (experienced surgeons achieve <1%), and selection bias inherent to the VA population

Outcome Summary Table

5. Key Clinical Trade-Off: Completeness of Revascularization

• OPCAB surgeons place fewer grafts on average (2.6 grafts vs 2.8 grafts per Cheng et al.)
• Achieving full multivessel revascularization on a beating, moving heart is technically harder
• Incomplete revascularization drives the higher reintervention rate and potentially the long-term mortality signal
• Highly experienced OPCAB surgeons can match graft numbers and patency of on-pump surgery - outcomes are highly surgeon-dependent

6. Patient Selection for OPCAB

Favorable candidates for OPCAB:

• Advanced age with severe aortic atherosclerosis ("calcified porcelain aorta") - aortic cross-clamping carries high embolic stroke risk
• Patients with severe systemic inflammatory states where CPB would be poorly tolerated
• Severe renal impairment (avoids hemodilution, pump-induced renal injury)
• Jehovah's Witnesses (minimizes transfusion)
• LIMA-to-LAD only procedures (technically simpler, least hemodynamic perturbation)

Less ideal for OPCAB:

• Complex multivessel disease requiring multiple posterior wall anastomoses (verticalization poorly tolerated)
• Severely impaired LV function (cannot tolerate the hemodynamic instability of cardiac positioning)
• Emergency/urgent cases where rapid revascularization is needed
• Significant intramyocardial coronary arteries

7. Anesthetic Considerations - Comparison

Where the Two Approaches Are Essentially the Same:

• Anesthetic technique (induction agents, opioid strategy, volatile agents for cardioprotection)
• Standard monitoring: invasive arterial line, 5-lead ECG, central venous access
• Fast-tracking goal: early extubation within 6 hours
• TEE: recommended for all OPCAB procedures (ASE/SCA guidelines)
• Volatile anesthetics may benefit OPCAB patients MORE due to preconditioning effects (some evidence)

Key Differences - OPCAB-Specific Anesthetic Considerations (Box 20.10):

Hemodynamic Management During OPCAB Cardiac Positioning:

Heart displacement/verticalization triggers:
  → ↓↓ Stroke volume + Cardiac index
  → ↑↑ CVP, RAP, PAP, PCWP
  → Large V waves (ischemic MR)
  → New RWMAs on TEE
  → ST changes, ECG amplitude loss

Anesthesiologist's Response:
  1. Trendelenburg positioning (head-down) → augments preload, partially corrects SV
  2. Volume administration
  3. Vasopressors (phenylephrine) → maintain CPP during anastomosis
  4. Inotropes (dobutamine, milrinone) if CO remains low → used in 79% of posterior wall cases (Mishra et al.)
  5. Maintain MAP ~60 mmHg during proximal aortic anastomosis
  6. NTG to treat coronary spasm or ischemia
  7. If irreversible: emergent conversion to CPB

8. Anticoagulation in OPCAB - Specific Controversy

• Low-dose heparin group: 100-200 IU/kg, targeting ACT 250-300 seconds
• Full-dose group: 300 IU/kg, targeting ACT >400 seconds
• Some surgeons continue antiplatelet drugs (including clopidogrel) until the day of surgery and restart them immediately post-op to reduce early graft thrombosis
• The 2024 meta-analysis by Khalil et al. (PMID 36858479) specifically examined optimal heparin dosing in OPCAB - this remains an active area of research
• Early graft occlusion post-OPCAB can cause sudden cardiac death - graft thrombosis risk is higher without the circuit-related heparin levels used in on-pump surgery

9. Conversion from OPCAB to On-Pump

• Conversion rate: ~8% across trials in low-to-moderate risk patients (20 trials)
• With experienced surgeons: <1%
• With less experienced surgeons (as in ROOBY trial): up to 12.4%
• Predictors of conversion: poor LV function, posterior wall disease, calcified or intramyocardial vessels
• CPB must always be primed and immediately available during every OPCAB case

10. Minimally Invasive Extensions of OPCAB

• MIDCAB: LIMA-to-LAD anastomosis through a small left anterior thoracotomy; avoids sternotomy; can be off-pump or on-pump via femoral cannulation
• TECAB (Totally Endoscopic): Robot-assisted complete revascularization through small chest wall ports; beating-heart TECAB avoids CPB; limited experience, outcome benefits not clearly established
• Hybrid Coronary Revascularization (HCR): MIDCAB/OPCAB LIMA-to-LAD + PCI stenting of non-LAD lesions; gaining traction for complex proximal LAD disease with other stentable vessels

11. Summary: Choosing Between Approaches

Recent evidence update: A 2024 meta-analysis of 28 RCTs (n=16,090) [PMID 38626442] found OPCAB reduces short-term stroke (OR 0.74, high-certainty evidence) but increases mid-term reintervention (RR 1.49) and long-term mortality (RR 1.09, moderate certainty) - findings that were not apparent in earlier smaller meta-analyses cited in the textbook. This reinforces that OPCAB's short-term procedural advantages do not translate into long-term survival benefit and may be reversed over time due to incomplete revascularization.