IJCS | Volume 31, Nº2, March / April 2018

100 Balzan et al. Atherosclerosis in the internal thoracic artery Int J Cardiovasc Sci. 2018;31(2)97-106 Original Article when one or more significant stenosis of coronary arteries may be revascularized, or cases of unacceptable angina in patients undergoing drug treatment. 2 After the establishment of the criteria for surgical indication, one should proceed to choose the type of graft to be used by the surgeon. The arterial options include the internal thoracic, radial, gastroepiploic, and inferior epigastric, and among the veins, the saphenous vein is chosen. The efficacy of the procedure is directly related to graft viability. According to the American Heart Association's latest Guideline for coronary artery bypass grafting (CABG), the use of the left internal thoracic artery (LITA) is preferred to revascularize the left anterior descending artery (AD) when indicated (Class IB). In cases of non-viability of the LITA, it is recommended to use the right internal thoracic artery (Class IC). 2 The internal thoracic artery, described by the Jena Nomina Anatomica in 1936, originates in the subclavian artery, appearing antero-inferiorly in the first part of the subclavian, about 2 cm above the clavicle, medially to the first rib. 13 In 4-30% of patients may arise from a common trunk along with other arteries that also originate in the subclavian, such as the thyrocervical trunk, suprascapular and lower thyroid arteries. 14 After its origin, it continues its course posterior to the brachiocephalic vein and medially to the scalene muscle anteriorly, descending vertically near the sternal border, and later crossing the six upper costal cartilages, ending at a bifurcation at the level of the sixth rib, giving rise to the superior epigastric and musculophrenic arteries. 15 The PREVENT IV study analyzed 1539 patients through selective angiography, in order to describe the number of LITA grafts for the anterior descending (AD) graft, in a period of 12 to 18 months after being submitted to coronary artery bypass grafting. We found 132 patients with significant stenosis of LITA, being considered as significant, a stenosis greater than or equal to 75%of the vessel diameter. Among the patients under study, 61 had total occlusion of the LITA, three had a subtotal stenosis, between 95 and 99%, and a stenosis between 75-95%. The same study carried out a four-year follow-up of these patients, in order to evaluate the rate of major outcomes, such as death, AMI, and revascularization, and to compare it with the group without significant stenosis. 16 In cases of stenosis (32% vs. 16.5%), clearly demonstrating the negative impact of graft patency on the prognosis of patients submitted to surgical treatment. The study considers as one of the main predictors of failure, non-significant left-sided stenosis, less than 75%; however, the study did not evaluate the presence of previous lesions through a control angiography performed prior to surgery, and it was not possible to relate the non-viability after previous atherosclerotic disease, or even its contribution to the long-term stenosis process. 16 The results of our study show that in the selected population of patients who are candidates for CABG, the prevalence of atherosclerotic lesions and lesions that impair LITA is significant, and this artery is not routinely evaluated by interventional cardiology, and it is difficult to make a clinical diagnostic, since patients are usually asymptomatic, and the changes are only evidenced by selective angiography. In one patient in our study, who underwent selective angiography during catheterization, the presence of atherosclerotic lesion in LITA was evidenced, with stenosis >70% (Figure 1). In order to differentiate from a possible vasospasm, infusion of 200mcg intra-arterial nitroglycerin was performed, where the subocclusive lesion remained (Figure 2). Taking into account the small number of the sample, 39 patients underwent cardiac catheterization with indication of CABG, the result is relevant, since in this patient the graft alteration used for myocardial revascularization was chosen, excluding the use of the LITA , due to the great risk of treatment failure and increased mortality. In 1993, Sons et al. 17 demonstrated the high prevalence of atherosclerotic lesions of LITA in patients with functional heart disease. The study analyzed 117 patients, all of whom had coronary artery disease (CAD), associated with valve abnormalities, or some other cardiac pathology. Atherosclerosis of the LITA was found in 11.1% of all patients investigated, indicating that risk factors such as the presence of peripheral arterial disease and hyperlipidemia deserve special attention in a patient with an indication for CABG, due to the high prevalence of the association of these factors with atherosclerosis of the main graft used for this surgery at the present time. Chen et al. 18 carried out a prospective study of LITA in eighty-six patients with indication for performing CABG. The investigation was performed through selective angiography of the LITA, during cardiac catheterization, seeking to evidence the presence of significant stenosis that could render the graft unfeasible. A significant lesion in the internal thoracic artery (1.2%) was found at the right subclavian artery, along with five other lesions (5.8%) that made its use unfeasible. The author considers as the only and important risk factor, the female sex. The study concludes that selective angiography of LITA during catheterization, especially in patients with indication for CABG, is a safe and necessary procedure, and should be