Long-term morphofunctional remodeling of internal thoracic artery grafts: a frequency-domain optical coherence tomography study

Resilience of the Internal Mammary Artery to Atherogenesis: Shifting From Risk to Resistance to Address Unmet Needs

Fueled by the global surge in aging, atherosclerotic cardiovascular disease reached pandemic dimensions putting affected individuals at enhanced risk of myocardial infarction, stroke, and premature death. Atherosclerosis is a systemic disease driven by a wide spectrum of factors, including cholesterol, pressure, and disturbed flow. Although all arterial beds encounter a similar atherogenic milieu, the development of atheromatous lesions occurs discontinuously across the vascular system. Indeed, the internal mammary artery possesses unique biological properties that confer protection to intimal growth and atherosclerotic plaque formation, thus making it a conduit of choice for coronary artery bypass grafting. Its endothelium abundantly expresses nitric oxide synthase and shows accentuated nitric oxide release, while its vascular smooth muscle cells exhibit reduced tissue factor expression, high tPA (tissue-type plasminogen activator) production and blunted migration and proliferation, which may collectively mitigate intimal thickening and ultimately the evolution of atheromatous plaques. We aim here to provide insights into the anatomy, physiology, cellular, and molecular aspects of the internal mammary artery thereby elucidating its remarkable resistance to atherogenesis. We propose a change in perspective from risk to resilience to decipher mechanisms of atheroresistance and eventually identification of novel therapeutic targets presently not addressed by currently available remedies.

Long-term graft patency after coronary artery bypass grafting: Effects of morphological and pathophysiological factors

OBJECTIVE

The aim of the present study was to identify morphological and pathophysiological factors associated with long-term patency of grafts used in coronary artery bypass grafting (CABG).

METHODS

A total of 127 patients who underwent CABG between 2000 and 2006 and presented for computed tomography evaluation of graft patency at 139.78±36.64 months post-CABG were analyzed. Patients received 340 grafts (2.68 grafts/patient), 399 distal anastomoses (3.14 anastomoses/ patient), 220 (55.14%) performed using arterial grafts, and 179 (44.86%) using saphenous vein grafts (SVGs).

RESULTS

Graft patency varied according to vessel type and coronary territory. Overall graft patency was 90.16% for the left internal thoracic artery (LITA), 75.55% for the right internal thoracic artery (RITA), 79.25% for the radial artery (RA), and 74.3% for the SVG. The maximum patency rate was obtained with the RA (80.65%) for the right coronary territory, RITA (92.86%) for the anterolateral territory, and SVG (82.54%) for the circumflex territory. The LITA-left anterior descending artery graft occluded in 13 (7.93%) cases, 7 due to competitive flow. The influence of graft length on patency rates after indexing to height was not significant. The target vessel degree of stenosis influenced arterial graft patency rates with an occlusion odds ratio (OR) of 3.02 when anastomosed to target vessels with <90% stenosis. Target vessel caliber also influenced patency rates with occlusion ORs of 2.63 for SVGs and 2.31 for arterial grafts when anastomosed to ≤1.5 mm target vessels.

CONCLUSION

Morphological parameters, such as graft type, target territory, target vessel caliber, and degree of stenosis, are important factors conditioning long-term graft patency.

Long-term graft patency after coronary artery bypass grafting: Effects of surgical technique

The aim of the current study was to identify surgical factors associated with long-term patency of grafts used in coronary artery bypass grafting (CABG). The present study analyzed data from 127 patients who underwent CABG at our institute between 2000 and 2006 and presented for ambulatory examination and coronary computed tomography angiography evaluation of graft patency in 2016 (139.78±36.64 months post-CABG). The 127 patients received 340 grafts (2.68 grafts/patient) and 399 distal anastomoses (3.14 anastomoses/patient), 220 (55.14%) with arterial grafts and 179 (44.86%) with saphenous vein grafts. Graft patency varied according to coronary territory, proximal anastomosis type (in situ graft, composite graft, graft anastomosed to the ascending aorta), Y anastomosis angle (47.21° for patent arterial grafts vs. 56° for occluded), and distal anastomosis angle (in sequential anastomoses irrespective to graft type, 48.60° for patent side-to-side anastomosis vs. 53.97° for occluded, 65.12° for patent end-to-side anastomosis vs. 90.80° for occluded; in single end-to-side anastomosis of arterial grafts, 39.46° for patent and 44.94° for occluded). A single end-to-side anastomosis angle 60° or greater was associated with a 5.149 occlusion odds ratio (OR) (P<0.001) for arterial grafts. Venous grafts were not sensitive to single end-to-side anastomosis angle. In conclusion, a small anastomosis angle for proximal Y and distal anastomoses is associated with a higher long-term patency of the free graft. Radial artery grafts registered higher patency rates when anastomosed to the ascending aorta compared with composite grafting with the left internal thoracic artery, whereas in situ right internal thoracic artery (RITA) anastomosed to the right coronary territory is associated with a lower patency rate compared with free RITA used to revascularise the anterolateral or circumflex territory in composite grafting.

Immediate and Long-Term Results of Drug-Eluting Stents in Mammary Artery Grafts

Percutaneous intervention of a coronary graft is the treatment of choice when the graft fails. The objective is to report the long-term results of drug-eluting stents (DES) in mammary artery grafts (MAG). Patients who had been treated with DES for MAG in 27 centers were selected. The baseline and procedural clinical data were included prospectively, and the follow-up was performed with the patients, families, and medical records. Two hundred and sixty-eight patients were included: age 65.5 ± 10.1 years, diabetes 47.8%, ejection fraction 55.5 ± 14.9%.

INDICATION

stable angina 28.4%, unstable angina 38.1%, non-ST-elevation myocardial infarction 21.6%, ST-elevation myocardial infarction 5.3%, and heart failure 6.7%; 1.19 ± 0.59 stents/patient were implanted measuring 18.8 ± 8.8 mm in length and 2.68 ± 0.35 mm in diameter. Rapamycin was used in 78 cases (29.1%), paclitaxel in 77 (28.7%), everolimus in 70 (26.1%), zotarolimus in 34 (12.7%), and biolimus in 9 (3.4%). All cases were successful except for 1 in which the patient died 30 minutes after the procedure. There were no other inhospital events. After a follow-up of 41 months (Q25: 23.7 to Q75: 57.8), 24 patients (9%) died of heart-related causes and 20 (7.5%) of noncardiac causes. Repeat revascularization was necessary in 31 cases, and in 1 additional patient, there was total occlusion, which was not treated. These 32 patients represented 11.9% of the total. In conclusion, the implantation of DES in MAG shows very high procedural success and also low long-term event rates.

Spontaneous spiral dissection of left internal thoracic artery graft

The left internal thoracic artery (LITA) is considered the most reliable coronary artery bypass grafting conduit due to its high rate of long-term patency. LITA grafts are extremely durable and associated complications are infrequent. We present a case with spontaneous spiral dissection of a LITA graft to the left anterior descending artery, which was assessed by optical coherence tomography (OCT) and intravascular ultrasound (IVUS). OCT was superior in visualizing the disrupted flap, false lumen, and intramural hematoma, but it did not visualize the full extent of the vessel wall. In contrast, IVUS allowed more complete and deeper vessel visualization, and thus better appreciation of the extent of intramural hematoma. Combined use of these two modalities provides complementary details on imaging of a LITA dissection.

Why is the mammary artery so special and what protects it from atherosclerosis?

The internal mammary artery (IMA) grafts have been associated with long-term patency and improved survival as compared to saphenous vein grafts (SVGs). Early failure of IMA is attributed to poor surgical technique and less with thrombosis. Similarly, bypass surgery especially with the use of IMA has also been shown to be superior at 1-year as well as over five years compared to percutaneous procedures, including the use of drug-eluting stents for the treatment of coronary artery disease. The superiority of IMAs over SVGs can be attributed to its striking resistance to the development of atherosclerosis. Structurally its endothelial layer shows fewer fenestrations, lower intercellular junction permeability, greater anti-thrombotic molecules such as heparin sulfate and tissue plasminogen activator, and higher endothelial nitric oxide production, which are some of the unique ways that make the IMA impervious to the transfer of lipoproteins, which are responsible for the development of atherosclerosis. A better comprehension of the molecular resistance to the generation of adhesion molecules that are involved in the transfer of inflammatory cells into the arterial wall that also induce smooth muscle cell proliferation is needed. This basic understanding is crucial to championing the use of IMA as the first line of defense for the treatment of coronary artery disease.