Coronary Artery Bypass

Click on hyperlinked text for illustrations

View TSDA Curriculum Online for this topic

1. Indications
A. Stable angina
· Survival depends on all patient-specific risk factors, not just angina
· Class I/II if there is significant 3-vessel disease and some LV dysfunction
· Class I/II if there is significant 3-vessel disease, good LV function, and one or more important proximal stenoses
· Class III/IV if there is significant 3-vessel disease and sometimes 2-vessel disease, regardless of LV function
· Left main stenosis at least 50%, even if asymptomatic
· 2-vessel disease with severe proximal LAD stenosis or some LV dysfunction
· Rarely indicated for single vessel disease

B. Unstable Angina
· Stabilize initially with medical therapy
· Same indications as for stable angina, but more urgent
· Strongest indications are 3-vessel disease, LV dysfunction, and angina at rest

C. Other Situations
· Angina after acute MI has same indications; delay CAB for at least 1 week
· Emergent CAB for hemodynamic instability during acute MI can salvage over 50% of such patients
· Emergent CAB indicated if PTCA results in hemodynamic instability

2. Operative Technique
A. General strategy
· Goal is complete revascularization by bypassing all vessels with at least 50% stenosis
· Patency enhanced by grafting to larger vessels with good runoff

B. Vein graft preparation
· Avoid overdistension and spasm of the vein
· Multiple large varices render the vein unsuitable for grafting
· The vein should be untwisted, marked, and reversed for grafting

C. IMA preparation
· Begin dissection at 6th intercostal space
· Either a pedicle or skeletonized artery may be used
· Distal end not divided until just prior to anastomosis
· Avoid probing unless there is no bleeding from the cut end
D. Distal anastomosis
· Incise anterior wall of coronary longitudinally 4 to 6 mm
· Bevel vein end somewhat larger than coronary opening for most distal anastomosis
· Incise vein longitudinally 10-20% longer than coronary opening for sequential anastomosis
· Sutures run from inside to out on the coronary and outside to in on the vein graft

E. Proximal anastomosis
· Lateral openings on the aorta are preferred to protect the grafts during reoperation
· Bevel vein end somewhat larger than aortic opening

3. Reoperative CAB
· Avoid manipulating intact grafts
· Some recommend replacing all vein grafts older than 6 years
· Others recommend only replacing vein grafts that are occluded or stenotic
· Left thoracotomy with femoral CPB is useful in the setting of a functional IMA-LAD graft

4. Vascular Anatomy
· CAD usually involves proximal portions of the 3 major arteries, particularly at branch points
· The LAD and RCA are more often involved than the CX
· 40% of patients studied for symptoms will have significant stenoses in all 3 vessels
· 95% of patients with 1 completely occluded artery will have a significant stenosis in at least one other artery
· 10-20% of patients with significant disease will have L main involvement
· Diffuse distal disease unsuitable for CAB is uncommon

5. Results
A. Survival
· Current hospital mortality is about 3%, most from acute cardiac failure
· 5-year survival is 88% and 10-year survival 75%
· IMA graft favorably affects the mid- and long-term survival (after 6 years)
· About 25% of all deaths after CAB are unrelated to ischemic heart disease or CAB

B. Risk factors for death
· Diminished LV function
· Unstable angina
· Acute hemodynamic instability after MI
· Operation within 1 week of acute MI
· Cardiogenic shock at time of operation
· Older age

C. Procedural risk factors for death
· Incomplete revascularization
· Nonuse of IMA to LAD
· Increased myocardial ischemic time
· Increased CPB time
· Earlier date of operation

D. Freedom from angina
· About 60% of patients are free from symptoms at 10 years
· Late recurrence is due to vein graft occlusion or progression of native coronary disease
· Risk factors for return of angina are not as powerful as those for death

E. Freedom from MI
· Perioperative incidence is 2-5%
· 5-year freedom is greater than 95% after CAB
· Survival is adversely affected by any post-CAB infarction

F. Freedom from sudden death
· Uncommon after CAB; 97% freedom at 10 years
· Poor preoperative LV function is the most significant risk factor for sudden death postop
· Successful CAB does not affect the incidence of existing ventricular arrhythmias, as most of these are due to scar

G. Neurologic events
· Up to 75% of patients may have subtle neurologic deficits in the perioperative period
· Gross neurologic defects occur in less than 1% of younger patients but up to 5% of patients over age 70

H. Functional status
· Maximal exercise capacity is improved, particularly when complete revascularization has been performed
· Systolic function in hypokinetic, akinetic and even dyskinetic areas can be improved
· A preop EF of 30% or less limits recovery of LV function after CAB
· Exercise testing at 2 weeks postop in most patients shows a normal rise in EF, a normal increase in LVEDV, and the resolution of regional wall motion dysfunction.

6. Graft History
A. Vein grafts
· Intimal hyperplasia is a universal finding after one month, but is not progressive
· At 1 year, the graft diameter approximates the recipient coronary diameter
· 10% close within the first few weeks if antiplatelet therapy is not used
· 10-year patency is about 50-60%
· Most grafts have evidence of atherosclerotic changes at 10 years

B. IMA grafts
· Intimal hyperplasia also develops; the IMA is highly resistant to atherosclerosis
· 10-year patency is about 90%
· 5-10% develop late stenoses, but most of these do not progress to occlusion
· Controversy exist over its use as a sequential graft and for bilateral IMA grafting

C. Other conduits
· Long-term patency not yet conclusive on gastroepiploic, inferior mesenteric, and inferior epigastric arteries
· The free radial artery graft is being re-evaluated for long-term patency

7. Reintervention after CAB
· Most interventions are reoperative CAB, although PTCA used in about 25% of cases
· 90% of patients are free from reoperative at 10 years
· Vein graft stenosis is the most common cause for reoperation
· IMA grafting reduces reoperations and extends time to reoperation
· Overall risk for reoperative CAB is about twice that of first CAB
· 10-year survival after reoperative CAB is about 65%