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.
C. Other arterial grafts
Radial grafts have similar 1-year patency to SVGs, but very low attrition rate beyond the first year and better long-term patency (85% at 5 years).110,111 Radial grafts are very prone to spasm and more prone than any other graft to early failure if the underlying native stenosis is not severe or the target artery is not large. They are probably best used when stenosis is >90% and the recipient artery is very large.111 Moreover, radial grafts are more susceptible to atherosclerosis than mammary arteries.
RIMA may also be used, as in-situ or free graft, mainly for RCA or LCx. It may be used as a free rather than in-situ graft to the distal RCA and sometimes LCx branches, because RIMA may be too short to reach these branches. RIMA has a better patency than radial and SVG grafts but may be technically more challenging with a risk of sternal wound infection, especially in patients with diabetes.112
The gastroepiploic artery may be used as a free or in-situ graft.
A classical CABG surgery involves grafting a LIMA to the LAD, one or several SVGs to diagonal(s), obtuse marginal branch(es), and distal RCA (or its PDA or PLB branch). Instead of SVGs, radial or free RIMA grafts may be used.
In distal left main disease, both the LAD and one of the obtuse marginal branches are bypassed.
D. Grafts with multiple distal anastomoses (see Chapter 34, Figure 34.41)
Some grafts connect to two or multiple distal targets. A sequential graft (or jump graft) connects to one branch, e.g. OM1, in a side-to- side anastomosis, then continues and connects to another branch, e.g., OM2, in an end-to-side anastomosis. A split graft (or Y graft) consists of a graft A that connects to one branch and a second graft B that is anastomosed to graft A and that separately connects to another branch. Sequential and split grafts reduce the number of aortic anastomoses and may improve patency in light of the higher flow across the graft. However, when the runoff is good, grafts with single targets have a higher patency than sequential grafts.104,105 Sequential grafting is useful in patients with poor runoff or patients with limited venous conduits (e.g., varicose veins). The best sequential graft patency is obtained by placing the last distal anastomosis onto the coronary branch with the greatest runoff, while the smaller coronary branch is anastomosed more proximally in a side-to-side fashion (e.g., graft to diagonal and LAD, LAD being the last anastomosis); this allows an increase in flow throughout the whole graft.105
E. Off-pump CABG
During on-pump CABG, the aorta is cannulated and cross-clamped, and a cardiopulmonary bypass (heart–lung pump) is used between the venae cavae and the aorta. Cardioplegia is then induced, and the pulmonary ventilation is turned off. The arrested heart is not perfused and is thus ischemic: this is reduced by rapid and cold cardioplegia, and limiting “pump time”. Off-pump CABG is performed on a beating heart without cardioplegia and aortic cannulation, although partial aortic cross-clamping is still needed if SVG anastomoses are performed.
Off-pump CABG has the advantage of less bleeding/less requirement for transfusion, less renal failure, less respiratory complications, and probably less stroke as aortic manipulation is limited.113,114 In fact, in patients with heavy aortic calcifications or atherosclerosis, off- pump CABG with only LIMA or LIMA and RIMA grafting is particularly valuable, as it avoids aortic manipulation. Off-pump CABG is, however associated with less complete revascularization and a higher risk of early ischemia and graft failure.113 MIDCAB (minimally invasive direct CABG) is a form of off-pump CABG performed through a mini-thoracotomy between two ribs, and mainly consists of single-vessel grafting of the LIMA to the LAD. Off-pump LIMA–LAD may be used as part of a hybrid strategy, where non-LAD disease is treated with PCI.
Appendix 2. Coronary vasospasm (variant angina, Prinzmetal angina)
A. Underlying CAD: patterns of vasospasm
While Prinzmetal angina was initially described in patients who had underlying obstructive CAD, sometimes unstable CAD,4,5,115,116 later reports suggest that vasospasm is also commonly diagnosed in patients with typical angina and no obstructive CAD.6 Even when the coronary arteries appear angiographically normal, IVUS imaging demonstrates that the sites of vasospasm exhibit underlying atherosclerosis. Atherosclerosis induces endothelial dysfunction and dysregulation of nitric oxide production, which leads to local vascular hyperreactivity.7
Vasospasm may be epicardial and focal, i.e., involving one coronary segment, or epicardial and diffuse, involving two or more coronary segments. It may also occur solely at the microvascular level.
Additional features of vasospasm:
Epicardial vasospasm often involves one site and recurs at the same atherosclerotic site; less commonly, it may involve multiple sites, sometimes two separate coronaries, or occur at separate sites at different times (~15% of cases).117
The LAD and RCA are most involved. The proximal and distal segments have been variously involved in different reports.
In the absence of CAD, spontaneous remissions within 6–12 months of follow-up or remissions with CCBs are common (up to 83% of patients). Yet up to a third of these patients may experience recurrences.116-119
Vasospasm that occurs without significant CAD is more commonly seen in women,6,120,121 although some series suggest it is more common in men.115, 116, 119 It is generally described in patients >40 years of age, with a mean age of 55–65, and is more prevalent among Asian populations. Smoking and chronic alcohol or cocaine use increase the risk of vasospasm.
B. ECG, arrhythmias, and clinical manifestations
Vasospasm usually leads to a more severe ischemia than fixed stenosis and is occlusive or subtotally occlusive, particularly when it occurs on top of obstructive, fixed stenosis. It typically leads to transient ST elevation, reflecting transmural ischemia, but it may also lead to ST-segment depression when the spasm is not totally occlusive. Post-ischemic T-wave inversion may be seen. Since ischemia may be severe, serious arrhythmias (VT, VF, AV block), syncope, sudden death, or MI may be seen. The combined risk of