Читать книгу Practical Cardiovascular Medicine - Elias B. Hanna - Страница 217

LIMA graft is usually used as an in-situ graft: the distal part of the LIMA is connected directly to the LAD, while the proximal LIMA is not touched and remains connected to the subclavian artery. LIMA atherosclerosis is extremely uncommon, hence the excellent long-term patency of 90% at 10 years; a LIMA that is patent beyond the first few months post-CABG usually remains patent for life. LIMA has an intact internal elastic membrane that prevents smooth muscle migration and atherosclerosis. Early LIMA failure is possible, however, and is related to anastomotic fibrointimal hyperplasia or to poor LIMA development. LIMA may not develop or may regress because of a subclavian stenosis, poor distal LAD flow, or insignificant proximal LAD stenosis. Significant native proximal disease is necessary to allow SVG and, more particularly, LIMA and radial grafts to remain patent; a good native flow may impede SVG or LIMA flow, leading to thrombosis of the SVG or spasm of an arterial graft. In fact, bypassing a LAD that has <50–60% stenosis leads to disuse atrophy of the LIMA or “string sign” in up to 80% of patients.

Always attempt to use LIMA to the LAD, except in emergent cases with hemodynamic instability, where SVG-to-LAD may be preferred, because SVG has a higher and more expeditious flow initially.¹⁰⁴ Also, LIMA is occasionally avoided in patients with severe lung disease in order to avoid pleural dissection and the subsequent left pleural effusion.

While LIMA does not develop atherosclerotic disease, ischemia of the LIMA territory may be caused by:

1 Subclavian stenosis (this is the most common cause of LIMA ischemia). The assessment of BP in both arms is critically important in CABG patients presenting with angina.

2 Atresia of the LIMA graft related to insignificant proximal LAD disease, poor distal LAD runoff, or subclavian stenosis. It is usually seen early after CABG.

3 Stenosis of the LIMA-to-LAD anastomosis, which often occurs in the first 3–6 months and results from intimal hyperplasia. Since it is not due to an atherosclerotic process, plain angioplasty provides good long-term patency (as good as BMS). Stenting may be reserved for a suboptimal result but is more systematically used in the DES era.

4 Progression of native LAD disease distal to the anastomosis.

5 If the LIMA’s intercostal branches are not clipped, the flow may be directed away from the LAD (steal phenomenon). However, this is an unlikely cause of myocardial ischemia, as the coronary flow is mainly diastolic, while the flow into the intercostal branches is mainly systolic.