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Abstract & Commentary
Synopsis: Presence of a significant brachial gradient is thus an ominous sign for diffuse atherosclerotic disease at an advanced stage and should alert the surgeon to the risk of severe atherosclerosis of the aorta and its branches.
Source: Baribeau Y, et al. Circulation. 2002; 106(12 Suppl I):I11-I13.
The incidence of hemodynamically significant subclavian artery stenosis in patients referred for coronary artery bypass graft (CABG) surgery has been estimated to be 0.5-2.3%. Significant subclavian stenosis proximal to the left internal mammary artery (LIMA) can result in inadequate flow in the LIMA graft, and hence in the grafted myocardial distribution, resulting in incomplete revascularization or coronary artery steal. In the present era, the vast majority of patients undergoing CABG will receive a LIMA graft, and importantly, as studies such as BARI would suggest, will derive the majority of mortality benefit from a properly constructed and functional LIMA graft. A small study from our institution demonstrated that a noninvasive brachial blood pressure differential of 15 mm Hg identified all patients with ³ 50% subclavian artery narrowing and that routine preoperative subclavian angiography was not useful in patients without a blood pressure differential.1 The presence of atherosclerotic disease in the arch and great vessels has further implications for the surgeon, and may affect not only the decision about how a LIMA graft will be handled (pedicled or free), but also has implications for placement of cross clamps, cardiopulmonary bypass cannulae and aortotomies at the time of CABG. Baribeau and colleagues sought to review the clinical and therapeutic implications of a difference in arm blood pressure detected preoperatively in patients undergoing cardiac surgery at their institution.
Patients who underwent cardiac surgery and had bilateral arm blood pressures were included in this analysis. A significant brachial gradient was defined as a difference of greater than or equal to 15 mm Hg between sequential systolic pressures measured in the right and left arms. Group 1 consisted of 53 patients with a significant brachial gradient and group 2 consisted of 175 patients without a significant brachial gradient. All patients had preoperative carotid duplex performed (severe stenosis defined as > 80%), and all patients had intraoperative epiaortic ultrasound of the ascending and transverse aorta (mild disease < 3 mm intimal thickness, moderate disease 3-5 mm intimal thickness, and severe disease > 5 mm intimal thickness or mobile/protruding atheroma). Baseline characteristics were similar between the 2 groups except that patients in group 1 (with significant brachial gradient) were more likely to have peripheral vascular disease (67.9% vs 26.2%; P = 0.0001) and a history of cerebrovascular symptoms (TIA or stroke) (26.4% vs 12.0%; P = 0.0196).
Carotid duplex scanning revealed severe internal carotid artery disease in 41.5% of group 1 patients and in only 13.71% of group 2 patients (P < 0.0001). Of note, only 35% of aortic disease identified as severe by epiaortic ultrasound were recognized by direct palpation intraoperatively. In group 1, subclavian or arch angiography was performed in 32 patients (60.4%) and 23 of these patents were found to have significant left subclavian stenosis or occlusion.
Baribeau et al describe multiple "strategic maneuvers" that were used intra-operatively in response to this information, including subclavian stenting, use of the right internal mammary artery graft or free left internal mammary graft, and minimizing manipulation of the aorta including axillary cannulation for cardiopulmonary bypass and beating heart surgery. While not an endpoint of this analysis, despite their higher risk profile, there was a trend toward decreased perioperative strokes in group 1 (13.20% vs 5.14%; P = 0.06). They conclude that the "presence of a (significant brachial) gradient is thus an ominous sign for diffuse atherosclerotic disease at an advanced stage and should alert the surgeon to the risk of severe atherosclerosis of the aorta and its branches."
Comment by Sarah M. Vernon, MD
As our population ages and our percutaneous revascularization techniques improve, the patients referred for cardiac surgery represent an increasingly high-risk group, with comorbity and overall atherosclerotic burden that places them at high risk for peri-operative complications. A significant proportion of these neurologic complications such as stroke, TIA, or postcardiopulmonary bypass cognitive deficits (which the surgeons refer to as "pump-head") are likely mediated in part by great vessel and arch disease. There is nothing earth shattering about this report, from the New England Heart Institute derived from a small group of patients undergoing cardiac surgery. The study does not prove that brachial blood pressure screening results in improved outcomes for patients undergoing cardiac surgery. Nonetheless, it demonstrates that a very simple, cost-effective maneuver (bilateral brachial blood pressure determination) might help identify a subgroup of patients who might likely be at increased risk for adverse perioperative events, namely those with severe aortic arch atherosclerosis. A 15 mm Hg brachial blood pressure differential can identify which patient might be better served with the additional information derived from great vessel angiography at the time of catheterization, preoperative carotid Duplex scanning, or intraoperative epiortic ultrasound. Identification of the patient with advanced atherosclerotic aortic disease might then allow the surgeon to better plan the safest approach to providing the most optimal revascularization. Ongoing clinical trials weighing the merits of cardiopulmonary bypass compared to the off-pump approach, for example, will eventually shed more light on how best to manage the patient with advanced vascular disease undergoing cardiac surgery. In the meantime, Baribeau et al remind cardiologists that something as simple as bilateral blood pressure measurements, might point us in the right direction.
Dr. Vernon is Assistant Professor of Medicine Director, VAMC Cardiac Catherization Laboratory University of New Mexico Health Sciences Center Albuquerque, NM.
1. Osborn LO, et al. Catheterization and Cardiovascular Intervention. 2002;56:162-165.