**6. Arterial graft failure**

The need for repeat revascularization is substantially reduced with the use of arterial conduits, since long-term patency is much higher compared to SVG. [66-68] In contrast to SVG, arterial grafts appear to be more resistant to the influence of atherogenic factors and incur only minor traumatic and ischemic lesions, since they are not removed from the blood circulation but are prepared locally, with few ligations and preservation of blood flow. [69] Since 1986, the LIMA has been used in more than 90% of CABG procedures. Less frequently, the RIMA is used. The early patency of a LIMA anastomosed to the left anterior descending (LAD) is reported to be almost 99%. [70] The mean patency of LIMA to coronary conduit at 5 years is reported 98%, at 10 years it is 95%, and at 15 years it is 88%. [71] Differences are observed between territory grafted, the 10 year LIMA patency to the LAD is reported to be 96% and to the circumflex (Cx) 89%. [72] The early patency of the RIMA anastomosed to major branches of the left circumflex artery is approximately 94%. [70] The mean RIMA patency at 5 years is reported to be 96%, at 10 years it is 81% and at 15 years it is 65%. [71] Again differences are observed, the RIMA graft patency to the LAD artery is 95% at 10 years and 90% at 15 years. Ten-year RIMA patency to the Cx marginal is 91%, right coronary artery is 84%, and posterior descending artery is 86%. [72] In situ RITA and free RITA had similar ten-year patency, 89% vs 91% respectively. RA patency is reported to range between 83% to 98% at 1 to 20 years but lower rates have been reported. [73] The patency rate estimated by the Kaplan-Meier method for the GEA conduit was 96.6% at 1 month, 91.4% at 1 year, 80.5% at 5 years, and 62.5% at 10 years. [74] Arterial grafts are not uniform in their biological characteristics and difference in the perioperative behaviour and in the long-term patency may be related to different characteristics. It should be taken into account in the use of arterial grafts that some grafts need more active pharma‐ cological intervention during and after operation to obtain satisfactory results.

Although, the IMA is the most used conduit to restore the blood flow to the LAD, it is less easy to use because of its complicated preparation and postoperative complications. Specific reasons for not to use the RIMA may include additional time to harvest, concerns over deep sternal wound infection, myocardial hypoperfusion, and unfamiliarity. Besides the potentially deleterious effect on the vascular supply of the forearm and hand, potential spasm and size matching to target coronary artery are the main drawback for the use of RA in CABG. [75,76]

is supplied by the vaso vasorum and in addition through the lumen, whereas the veins are only supplied by the vaso vasorum [64]; 3) the endothelium of the arteries may secrete more endothelium-derived relaxing factor [65]; 4) the structure of the artery is subject to high pressure, whereas the vein is subjected to low pressure. While the SVG have to adapt to the high pressure, the arterial grafts do not which may partly explain the difference in the long-

**Type I - Somatic arteries** Less spastic Internal mammary artery

**Type II - Splanchnic arteries** Spastic Gastroepiploic artery

**Type III - Limb arteries** Spastic Radial artery

**Table 1.** Functional classification of arterial grafts according to physiological and pharmacological contractility,

Inferior epigastric artery Subscapular artery

Splenic artery Inferior mesenteric artery

Ulnar artery Lateral femoral circumflex artery

Similar like SVG, the arterial grafts can also be divided into three layers: the intima, media, and adventitia. As a result of location at different parts of the body and supply to different organs, differences in gross anatomy among arterial grafts have been observed. Divergent anatomic structures of the arteries have been observed. One of the most obvious differences is that arteries such as the GEA, IEA, and RA contain more smooth muscle cells in their walls and are therefore less elastic compared to other arteries such as the IMA which may be more elastic because they contain more elastic laminae. [64] Such structure divergence may also

The need for repeat revascularization is substantially reduced with the use of arterial conduits, since long-term patency is much higher compared to SVG. [66-68] In contrast to SVG, arterial grafts appear to be more resistant to the influence of atherogenic factors and incur only minor traumatic and ischemic lesions, since they are not removed from the blood circulation but are prepared locally, with few ligations and preservation of blood flow. [69] Since 1986, the LIMA has been used in more than 90% of CABG procedures. Less frequently, the RIMA is used. The early patency of a LIMA anastomosed to the left anterior descending (LAD) is reported to be almost 99%. [70] The mean patency of LIMA to coronary conduit at 5 years is reported 98%, at 10 years it is 95%, and at 15 years it is 88%. [71] Differences are observed between territory

explain the difference in phsysiologic and pharmacologic reactivity.

term outcome.

198 Artery Bypass

anatomical, and embryological characteristic

**6. Arterial graft failure**

Although all arterial grafts may develop vasospasm, it develops more frequently in the GEA and RA, than the IMA and IEA. [13,77] Two types of vasoconstrictors are found to be important spasmogens in arterial grafts. [78] Type I vasoconstrictors are the most potent and they strongly contracts arterial grafts even when the endothelium is intact. The constrictors are endothelin, prostanoids such as thromboxane A2 and prostaglandin F2α, and alpha1-adrenoceptor agonists. Type II vasoconstrictors induce only weak vasoconstriction when the endothelium is intact, but play an important role in the spasm of arterial grafts when the endothelium is destroyed by surgical manipulation. Type II vasoconstrictor is 5-hydroxytryptamine.

Early IMA graft failure is attributed to technical errors and distal anastomosis. [79,80] Non‐ technical factors that may affect the patency of the arterial graft are high levels of LDL cholesterol and triglycerides, and high levels of lipoprotein(a), a thrombogenic molecule that is related to the hypercoagulable state. Other classical risk factors for coronary artery disease, such as diabetes mellitus, smoking and hypertension may also affect the patency of the arterial graft. Age may be of influence the quality of the arterial graft.

Furthermore, competitive flow and low-flow profoundly affect graft patency. Low-grade graft stenoses in the target artery proximally are a major cause of competitive flow which may lead to a decrease in antegrade flow in the arterial graft causing early failure ('disuse athrophy'). The SVG and IMA are more tolerant than the RA and GEA conduits. This is likely to be related to biological differences as the RA and GEA have a thick layer of smooth muscle or poor endothelial function in these muscular conduits. Therefore, it is recommended to avoid grafting target arteries with a stenosis less than 90% with RA grafts. [81]

Atherosclerosis in arterial grafts can develop before coronary grafting when the graft is in the in situ native position, or after. The incidence of atherosclerosis in native arteries in the in situ position in the four major arterial grafts is low, especially in the IMA. [64] The incidence of atherosclerosis in bypass grafts is also low, in IMA grafts even as late 15 to 21 years after CABG. [67,82] However, the degree of stenosis in the native vessel is a major predictor of IMA graft patency. The observed association between non-significant stenosis of the native artery and high occlusion rate of the arterial bypass conduit raises concerns about the use of IMA in the treatment of native vessels with only mild or moderate stenosis. [83] In addition, the target vessel for the IEA must be one that is completely occluded or severely stenotic, with low coronary resistance, and in territories not totally infarcted to avoid "string sign" (conduit <1 mm diameter). Although the incidence of atherosclerosis is low in arterial grafts, 2 other morphologic changes may be present in arterial graft, fibrointimal proliferation and fibrosis representing organized thrombus. [84] The presence of fibrointimal proliferation is associated with long-term IMA graft narrowing and may be an important factor for late graft failure. Despite hypertension was associated with increased fibrointimal proliferation in SVG, this correlation could not be found in IMA grafts. [84]

and controlling serum glucose in diabetic patients. The bypass angioplasty revascularization investigation (BARI) trial illustrated that intensive risk-factor modification and hypolipid medication use slows atherosclerosis progression within native coronary arteries of CABGtreated patients and may to a lesser extent improve long-term patency of surgical conduits. [89] *Antiplatelet therapy* - Antiplatelet therapy is recommended following CABG since it improves SVG patency and clinical outcomes. The 2008 EACTS guideline on antiplatelet and anticoa‐ gulation management in cardiac surgery [90] recommends that aspirin should be given postoperatively to all patients without contra-indications after CABG in order to improve the long-term patency of SVG. The recommended dose given is 150—325 mg. Several studies have shown a trend towards maximal benefit with 325 mg/day in the first year. [91-95] In contrast, there is no evidence that the use of aspirin after coronary artery bypass grafting improved the patency of arterial grafts. However, aspirin may be recommended on the basis of improved

Treatment of Coronary Artery Bypass Graft Failure

http://dx.doi.org/10.5772/54928

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The optimal timing of the first dose of aspirin for patients after CABG was investigated in a meta-analysis of 12 studies and found that the benefit of aspirin was optimal if started at 6 h after surgery. [96] Although, the largest risk reduction was observed when aspirin was given at 1 h after operation, there was a non-significant increase in the rate of re-operation in this group. [91] In contrast, there was no benefit found in giving aspirin if starting more than 48 h

Whether clopidogrel given in addition of aspirin to high-risk patients after CABG would reduce thrombotic complications was evaluated in several studies. Registry data showed that adding clopidogrel to aspirin was independently associated with a decrease in recur‐ rence of anginal complaints and adverse cardiac events following off-pump CABG. Nonetheless, clopidogrel use beyond 30 days did not show a significant effect on adverse cardiac events. [98] In the randomized CASCADE (Clopidogrel After Surgery for Coro‐ nary Artery Disease) study, aspirin monotherapy was compared with aspirin plus clopi‐ dogrel in 113 patients undergoing CABG and SVG intimal hyperplasia was determined by intravascular ultrasound at 1 year. [99] Compared with aspirin monotherapy, the combination of aspirin plus clopidogrel did not significantly reduce SVG intimal hyper‐ plasia 1 year after CABG. Although the study was not powered for clinical outcomes, there was no significant difference in SVG patency or cardiovascular events, neither was there a difference in the incidence of major bleeding between the 2 treatment groups at 1 year. Moreover, the superiority of clopidogrel over aspirin for optimising graft patency after CABG has not been established and thus aspirin should be regarded as the drug of

postoperatively. [97] Practically, Aspirin should be commenced within 24 h of CABG.

first choice, however, clopidogrel is an acceptable alternative to aspirin. [90]

In patients whom underwent CABG for ACS subgroup analyses of the CAPRIE (Clopidogrel versus Aspirin in Patients at Risk of Ischemic Events) and CURE (Clopidogrel in Unstable angina to prevent Recurrent Events) study provides supportive evidence to prescribe clopi‐ dogrel for 9 to 12 months in addition to aspirin. [100,101] In patients undergoing coronary bypass surgery with a coronary stent in situ implanted within 1 year, clopidogrel should be continued if the stented vessel has not been grafted. Finally, in patients with SVG failure treated

survival of patients in general who have atherosclerotic disease.
