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REDO CABG WHEN SVG TO LAD IS PATENT....WHICH CONDUIT?

Regarding the question about bypassing a LAD with patent vein grafts, I found a few interesting pieces of information which I want to share with you.

In the chapter on "Repeat CABG for myocardial ischemia" in Sabiston and Spencer's textbook SURGERY OF THE CHEST, Ed 6, 1995, Dr.Floyd Loop deals in detail with the vexatious question of whether a vein graft that appears normal five years or more after the first operation should be replaced, when another vein graft is atherosclerotic in the same patient. According to Dr.Loop, the answer is probably YES, particularly when the normal appearing graft perfuses the LAD, and could be replaced with an ITA graft.

The factors which would guide such a decision are

1. pathoanatomic findings
2. extent of regional perfusion of that graft
3. status of myocardium in that region
4. patient's overall risk profile.

Minimal atherosclerosis in vein grafts by arteriography is usually underestimated, and generally proves to be more diffuse when examined after the graft is removed. Also, propensity of atherosclerotic disease to progress is unpredictable.

Marshall W.G., Saffitz J, and Kouchoukos NT ( Ann.Thorac.Surg. 42:163,1986) recommend routine replacement of all vein grafts at the time of reoperation if performed five years or more after the initial procedure.

Another fascinating paper in this connection is the one titled "IS THE INTERNAL THORACIC ARTERY THE CONDUIT OF CHOICE TO REPLACE A STENOTIC VEIN GRAFT ?" from the Cleveland Clinic Foundation ( Navia D, Cosgrove DM, Lytle BW, Taylor PC, McCarthy PM, Stewart RW, Rosenkrantz ER and Loop FD Ann. Thorac.Surg. 1994;57:40-44).

387 patients with blocked SVG to LAD were grouped into 4 categories:

1. New SVG to LAD, removal of old graft
2. ITA to LAD, old graft left alone
3. ITA to LAD, with SVG to diagonal, old graft interrupted
4. ITA to LAD alone, old graft interrupted.

The risk of reoperation for blocked SVG is embolisation of atherosclerotic debris with intra op myocardial infarction. Conventionally it has been advocated that this be minimised by no touch dissection and complete interruption of the involved vessel as early as possible. The question then was of the most appropriate conduit to replace the vein graft.

In their group 4 patients, Navia et al found a high incidence of HYPOPERFUSION SYNDROME, due to potential imbalance between supply and demand. This may be due to:

a. decreased flow due to small ITAs or injury to ITA with suboptimal flow ( LEVINSON"s rule may be useful here !!! ) (or)
b. increased demand as occurs in
- i) hypertrophied myocardium
- ii) dilated ventricles
- iii) entire septal blood supply from LAD due to complete occlusion of RCA.

That the ITA is the culprit is evidenced by the fact that

a. the syndrome was localised to group 4 - interrupted SVG with ITA to LAD
b. absence of syndrome when old SVG was left intact
c. when a fresh SVG was placed distal to the ITA anastomosis in 11 patients who developed hypoperfusion syndrome, a dramatic improvement was seen.

Since the problem was not seen in ALL group 4 patients, (the majority tolerated the op well), the difference may be a function of amount of myocardium supplied by the LAD. (however, this cannot be predicted at the present time).

The CURRENTLY AVAILABLE OPTIONS then would be:

1. Replace old SVG with fresh SVG....Advantages : a. no atheroembolism b. adequate perfusion through the wide SVG. Suitable for older patients, when long term advantages of ITA are not applicable.
2. Divide old SVG, ITA to LAD, and new SVG to diagonal or LAD proximal or distal to the ITA, as a supplement. Dr.Denton A.Cooley refers to this as the "belt and braces" approach !! Advantages are no atheroembolism and adequate flow.
Potential disadvantage is competitive flow with "string sign" of ITA on angio, and ITA 'atrophy'. Clinical implications of this problem are uncertain. An atretic appearing ITA may be able to dilate and function normally if competitive flow is decreased and demand increased ( Refs: 1. Dincer B, Barner HB. The "occluded" internal mammary artery graft. Restoration of patency.... J.Thorac.Cardiovasc.Surg. 1983;85:318-320 2. Aris A, Borras X, Ramio J. Patency of IMA grafts in no flow situations J.Thorac.Cardiovasc.Surg. 1987;93:62-4) But, although encouraging, these reports represent a combined observation of fewer than 10 patients total, and additional clinical and experimental studies are needed.
If ITA recanalisation is proved, this may be the best option, since atheroembolism and hypoperfusion are avoided, and long term patency advantages of ITA grafting are available.
3. Leave the old graft, and add a ITA to LAD. This provides adequate flow, but has the risks of atheroembolism and competition to ITA flow with string sign. This may be a viable option, going by the outcome of group 2 patients.
The policy of interrupting the old vein graft to totally blocked LAD, and replacing with ITA alone, however MUST BE STRONGLY DISCOURAGED, since there is a high incidence of death and hypoperfusion syndrome.

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S,SIVASUBRAMANIAN/sivaraj@giasmd01.vsnl.net.in/Reviewed last on 10th July,1996