Myocardial revascularization with internal mammary artery bypass: an emerging treatment of choice

Conduits' Biology Regulates the Outcomes of Coronary Artery Bypass Grafting

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Accelerated atherosclerosis is common when SVGs, but not arterial grafts, are used for myocardial revascularization during CABG.

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This review will provide an overview of the available data on the most commonly used conduits in CABG, highlighting the differences in their cellular biology, mechanical, biochemical, and vasoconstrictive properties.

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Clinical and scientific evidence support the use of arterial grafts over venous conduits at the time of CABG. These arterial conduits seem to be more protected toward the development of atherosclerosis. Exploring the molecular and cellular mechanisms, of the various cell populations within these conduits, will help unveil the pathways responsible for these protective effects.

Coronary artery bypass graft (CABG) is the gold standard for coronary surgical revascularization. Retrospective, prospective, and meta-analysis studies looking into long-term outcomes of using different conduits have pointed to the superiority of arterial grafts over veins and have placed the internal mammary artery as the standard conduit of choice for CABG. The superiority of the internal mammary artery over other conduits could be attributable to its intrinsic characteristics; however, little is known regarding the features that render some conduits atherosclerosis-prone and others atherosclerosis-resistant. Here, an overview is provided of the available data on the most commonly used conduits in CABG (internal mammary artery, saphenous vein, radial artery, gastroepiploic artery), highlighting the differences in their cellular biology, mechanical, biochemical, and vasoconstrictive properties. This information should help in furthering our understanding of the clinical outcomes observed for each of these conduits.

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.

Internal mammary angiography: a review of technical issues and newer methods

Up to 90% of coronary bypass operations in some centers now include at least one IMA graft. In parallel with the increased use of IMA grafts, our catheterization laboratory records for 1986-7-8 demonstrate a progressive increase in IMA angiography, both absolutely (11, 28, 48 cases/yr) and as a percent of restudy procedures performed after prior bypass (14, 25, 43%). Unfortunately, these records also show that cannulation of the right and left IMAs may involve substantial technical hurdles, resulting in a mean time of 19 +/- 19 min from catheter insertion to selective IMA angiography. Based on this experience, we review a standard technique for IMA angiography using preformed catheters, and describe alternative methods (including use of PTCA guidewires with or without super-selective catheters, and non-selective angiography utilizing a specially designed balloon occlusion catheter).

Nonselective preoperative digital subtraction angiography of internal mammary arteries

In preparation for coronary bypass surgery, digital subtraction angiography (DSA) was used to assess the caliber of the left and right internal mammary arteries and to exclude stenoses of their feeding arteries. In 100 patients (86 males, mean age 56 +/- 9 years) DSA was performed with a Siemens Digitron 2 device. A frontal projection was used in 18 patients, and a 10-20 degree right anterior oblique projection was used in 82 patients. The flow was 10 to 25 ml/sec; 20 ml was injected in 45 patients, 30 ml in 41, 40 ml in 5, 50 ml in 8, and 60 ml in 1 patient. Judged on the proximal third, visualization of the left and the right internal mammary artery was good in 80 and 72, fair in 17 and 20, and bad in 3 and 8 arteries, respectively. The diameter (mm) was 2.7 +/- 0.4 (range 1.8-3.4) and 2.7 +/- 0.3 (range 2.0-3.5), and visible length (cm) was 8 +/- 5 (range 1-24) and 9 +/- 4 (range 2-22) for the two arteries, respectively. The 10-20 degree right anterior oblique view separated the left internal mammary artery better from the descending aorta than the frontal view. In more pronounced right anterior oblique views the ascending aorta interfered with the right internal mammary artery. The quality was not different with 20 ml or 30 ml injections. The feeding arteries could not be assessed in 4 patients. One left subclavian artery was found occluded at the orifice. Incidentally, 2 distal right subclavian stenoses and 2 carotid stenoses were detected.(ABSTRACT TRUNCATED AT 250 WORDS)

Combined revascularization of coronary and femoral arteries: a proposed alternative

Two patients with both coronary artery disease and leg ischemia were successfully treated with a combined revascularization procedure. Coronary arteries were bypassed with in situ internal mammary artery grafts, and bilateral femoral arteries were bypassed with expanded polytetrafluoroethylene grafts descended from the ascending aorta through the preperitoneal abdominal wall tunnel. Both patients recovered well and experienced no angina or claudication.

Percutaneous transluminal angioplasty of left internal mammary artery grafts: two years' experience with a femoral approach

Percutaneous transluminal angioplasty via the femoral approach was attempted through internal mammary artery grafts in 11 patients who presented with distal anastomotic stenoses or distal native coronary artery stenoses and angina pectoris. The procedure was technically successful in 10 patients and no major complications occurred. During follow up there was one late death, but all 10 surviving patients showed functional improvement. Percutaneous transluminal angioplasty seems to be a safe and effective treatment for stenoses of internal mammary artery grafts. This is an effective technique for treating the increasing number of patients who are likely to present with stenoses of these grafts.

Fifteen-year results of coronary artery bypass for isolated left anterior descending coronary artery disease

During 1971 through 1975, 266 patients underwent primary coronary artery bypass grafting for occlusive disease confined to the left anterior descending coronary artery. Actuarial survival at 15 years was 72.7% with 60% of survivors being free from angina. Although the cause of death was cardiac related in 50% of the patients who died, survival was comparable with that of an age-matched and sex-matched general population. During follow-up, 48 secondary or tertiary repeat coronary artery bypass as well as 44 percutaneous transluminal coronary angioplasty procedures were performed. Acute event-free status (freedom from acute myocardial infarction, repeat coronary artery bypass grafting, percutaneous transluminal coronary angioplasty, or death) persisted at 15 years in 43.2% of patients. The differences in survival when patients were segregated according to age, sex, number of grafts performed, or graft conduit (internal mammary artery versus vein) were not significant. However, comparison of graft conduits revealed a significantly better (p = 0.02) overall acute event-free survival when the internal mammary artery was used.

A comparison of morphologic and angiographic findings in long-term internal mammary artery and saphenous vein bypass grafts

Internal mammary artery grafts are currently considered the conduits of choice for myocardial revascularization. Comparisons of long-term morphologic changes in internal mammary artery grafts and saphenous vein grafts and correlation with premortem angiography have not been reported. Eighteen internal mammary artery and 15 saphenous vein grafts that had been in place for 12 to 118 months (mean 56) in 18 patients were removed either surgically or at necropsy and examined histologically. Premortem angiograms were performed within 1 month of histologic study in 15 of these patients. Fibrointimal proliferation was more frequent in internal mammary artery than in saphenous vein grafts 8 [( 44%] of 18 versus 4 [27%] of 15; p = NS). In contrast, atherosclerosis was common in saphenous vein grafts but was extremely rare in internal mammary artery grafts (10 of 15 versus 1 of 18; p = 0.01). A good correlation was noted between the degree of narrowing estimated by angiographic and histologic measurements in both internal mammary artery grafts (d = 0.90) and saphenous vein grafts (d = 0.71). Accelerated atherosclerosis did not occur in internal mammary artery grafts, but was common in saphenous vein grafts. Fibrointimal proliferation was commonly associated with graft narrowing in internal mammary artery grafts and may be an important factor in late graft closure. This study also confirms that internal mammary artery grafts have greater longevity compared with saphenous vein grafts.

Kinking of internal mammary grafts: report of two cases and surgical correction

Two patients who underwent left internal mammary artery (IMA) anastomoses to the left anterior descending artery (LAD) developed sudden angina associated with anterior ischemic changes on EKG in the early postoperative period, one at 4 hr and the other at 3 days following operation. Digitalized arteriography via retrograde injection of the left brachial artery revealed the IMAs, which were partially obstructed because of looping and Kinking, although the anastomoses to the LAD were patent. Reoperation was successful in relieving obstruction by reducing these abnormalities and resulted in an uncomplicated postoperative course following the second operation. Discussion of the etiology, radiological technique of diagnosis, correction, and prevention of this cause of internal mammary graft failure is presented.

The brachial artery method to transluminal internal mammary artery angioplasty

A new catheter technique to perform angioplasty of the right or left internal mammary artery coronary graft utilizing the brachial artery approach is described. Utilization of the ipsilateral brachial artery permitted cannulation of the internal mammary artery with preformed polyurethane Teflon-lined guide catheters. The coronary dilatation catheter was passed through the guiding catheter into the internal mammary artery. This technique permitted successful access into the ipsilateral mammary artery in eight patients, the left internal mammary artery graft in five and the right in three patients. The angioplasty procedure was successfully performed in seven of eight cases (spasm of the left internal mammary artery precluded successful dilatation catheter passage in one case). No brachial artery complications were encountered. In two cases, angioplasty was successfully performed in additional coronary vessels. Follow-up of 1-16 months (mean: 7.7 months) revealed no clinical evidence of restenosis. The ipsilateral brachial artery approach utilizing preshaped guiding catheters for visualization and introduction of dilatation catheters into the internal mammary artery graft is a safe and successful approach, and it is an acceptable alternative to the femoral technique.