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Coronary Artery Bypass

Coronary Artery Bypass

1. Indications

A. Stable angina
1) Survival depends on all patient-specific risk factors, not just angina
2) Class I/II if there is significant 3-vessel disease and some LV dysfunction
3) Class I/II if there is significant 3-vessel disease, good LV function, and one or more important proximal stenoses
4) Class III/IV if there is significant 3-vessel disease and sometimes 2-vessel disease, regardless of LV function
5) Left main stenosis at least 50%, even if asymptomatic
6) 2-vessel disease with severe proximal LAD stenosis or some LV dysfunction
7) Rarely indicated for single vessel disease
B. Unstable Angina
1) Stabilize initially with medical therapy
2) Same indications as for stable angina, but more urgent
3) Strongest indications are 3-vessel disease, LV dysfunction, and angina at rest
C. Other Situations
1) Angina after acute MI has same indications; delay CAB for at least 1 week
2) Emergent CAB for hemodynamic instability during acute MI can salvage over 50% of such patients
3) Emergent CAB indicated if PTCA results in hemodynamic instability

2. Operative Technique

A. General strategy
1) Goal is complete revascularization by bypassing all vessels with at least 50% stenosis
2) Patency enhanced by grafting to larger vessels with good runoff
B. Vein graft preparation
1) Avoid overdistension and spasm of the vein
2) Multiple large varices render the vein unsuitable for grafting
3) The vein should be untwisted, marked, and reversed for grafting
C. IMA preparation
1) Begin dissection at 6th intercostal space
2) Either a pedicle or skeletonized artery may be used
3) Distal end not divided until just prior to anastomosis
4) Avoid probing unless there is no bleeding from the cut end
D. Distal anastomosis
1) Incise anterior wall of coronary longitudinally 4 to 6 mm
2) Bevel vein end somewhat larger than coronary opening for most distal anastomosis
3) Incise vein longitudinally 10-20% longer than coronary opening for sequential anastomosis
4) Sutures run from inside to out on the coronary and outside to in on the vein graft
E. Proximal anastomosis
1) Lateral openings on the aorta are preferred to protect the grafts during reoperation
2) Bevel vein end somewhat larger than aortic opening

3. Reoperative CAB

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

4. Vascular Anatomy

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

5. Results

A. Survival
1) Current hospital mortality is about 3%, most from acute cardiac failure
2) 5-year survival is 88% and 10-year survival 75%
3) IMA graft favorably affects the mid- and long-term survival (after 6 years)
4) About 25% of all deaths after CAB are unrelated to ischemic heart disease or CAB
B. Risk factors for death
1) Diminished LV function
2) Unstable angina
3) Acute hemodynamic instability after MI
4) Operation within 1 week of acute MI
5) Cardiogenic shock at time of operation
6) Older age
C. Procedural risk factors for death
1) Incomplete revascularization
2) Nonuse of IMA to LAD
3) Increased myocardial ischemic time
4) Increased CPB time
5) Earlier date of operation
D. Freedom from angina
1) About 60% of patients are free from symptoms at 10 years
2) Late recurrence is due to vein graft occlusion or progression of native coronary disease
3) Risk factors for return of angina are not as powerful as those for death
E. Freedom from MI
1) Perioperative incidence is 2-5%
2) 5-year freedom is greater than 95% after CAB
3) Survival is adversely affected by any post-CAB infarction
F. Freedom from sudden death
1) Uncommon after CAB; 97% freedom at 10 years
2) Poor preoperative LV function is the most significant risk factor for sudden death postop
3) Successful CAB does not affect the incidence of existing ventricular arrhythmias, as most of these are due to scar
G. Neurologic events
1) Up to 75% of patients may have subtle neurologic deficits in the perioperative period
2) Gross neurologic defects occur in less than 1% of younger patients but up to 5% of patients over age 70
H. Functional status
1) Maximal exercise capacity is improved, particularly when complete revascularization has been performed
2) Systolic function in hypokinetic, akinetic and even dyskinetic areas can be improved
3) A preop EF of 30% or less limits recovery of LV function after CAB
4) 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
1) Intimal hyperplasia is a universal finding after one month, but is not progressive
2) At 1 year, the graft diameter approximates the recipient coronary diameter
3) 10% close within the first few weeks if antiplatelet therapy is not used
4) 10-year patency is about 50-60%
5) Most grafts have evidence of atherosclerotic changes at 10 years
B. IMA grafts
1) Intimal hyperplasia also develops; the IMA is highly resistant to atherosclerosis
2) 10-year patency is about 90%
3) 5-10% develop late stenoses, but most of these do not progress to occlusion
4) Controversy exist over its use as a sequential graft and for bilateral IMA grafting
C. Other conduits
1) Long-term patency not yet conclusive on gastroepiploic, inferior mesenteric, and inferior epigastric arteries
2) The free radial artery graft is being re-evaluated for long-term patency

7. Reintervention after CAB

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