A 62-year old man with history of hypertension, dyslipidemia and stable angina is admitted to the hospital for elective coronary artery bypass graft (CABG) due to extended three vessel coronary disease. The patient has a history of left carotid artery revascularization with stenting due to severe stenosis 3 years ago and has a history of intermittent claudication and dyspnea with exertion that started 5 months ago. The patient undergoes elective CABG operation of left circumflex (LCX) and left anterior descending (LAD) coronary arteries, utilizing a left saphenous vein conduit and the left internal thoracic artery (ITA) respectively. The surgery completes uneventfully but after 24 hours the patient complains of acute pain in his lower left foot. Clinical examination reveals a pale, not swollen, cold limb with faint distal pulses. His vitals are unrevealing. Computed tomography (CT) angiography demonstrates 80% stenosis of the abdominal aorta due to extensive atheromatous disease and an occluded left common iliac artery. The patient eventually undergoes emergent revascularization.
Which is the pathophysiologic mechanism of patient's acute limb ischemia?
Show Answer
The correct answer is: C. Lack of collateral circulation
Patients with occlusion at the aortoiliac (e.g. thrombosis of the abdominal aorta) level usually have a collateral blood flow to the ipsilateral iliac artery (Winslow's pathway) through anastomoses between the superior epigastric (branch of ITA) and the inferior epigastric arteries.1 However, when blood flow through those collateral pathways is interrupted (e.g. in this case the ITA was used as a graft for the bypass surgery), severe limb threatening ischemia could be caused, if the blood flow through aorta diminishes.2 Thus, patients with aortoiliac occlusive disease are at higher risk for limb threating ischemia if they undergo CABG utilizing the ITA.3,4
To prevent limb ischemia, patients with severe peripheral artery disease (PAD) should be carefully evaluated before they undergo CABG and in cases with lower limb blood flow depending on ITA collaterals, an alternative graft should be chosen. When collateral circulation from the ITA is not recognized preoperatively, intensive surveillance follow-up, checking the peripheral oxygen saturation in both lower extremities, is warranted.2 (Answer C)
Deep venous thrombosis could be a potential cause of acute limb pain in the setting of hospitalization after surgery. However, the clinical examination and the CT angiography findings make acute limb ischemia due to no collateral blood flow to the limb a more likely diagnosis for this patient with severe PAD. (Answer A)
Gangrene caused by lack of sufficient blood flow and bacterial infection could be a potential cause of acute limb pain. This patient is at high risk for dry gangrene due to extensive PAD. It is usually characterized by shriveled brown to purplish skin and develops gradually. The absence of fever, the findings of the CT angiography and the acute onset of limb pain makes this diagnosis unlikely. (Answer B)
Buerger's disease is a non-atherosclerotic disease, typically observed in young males, who are heavy smokers. In some cases, vasospasm can be present causing intermittent claudication. This patient is less likely to have femoral vasospasm due to Buerger's disease, given the acute onset of symptoms and the CT-angiography findings. (Answer D)
Educational Objective:
The internal thoracic-epigastric arteries are critical collateral pathways used to compensate for the occlusion of the infrarenal aorta and bilateral iliac arteries. But in cases where they are not present (e.g. CABG surgery) critical limb ischemia (CLI) and limb threat may occur.
References
Kim J, Won JY, Park SI, Lee DY. Internal thoracic artery collateral to the external iliac artery in chronic aortoiliac occlusive disease. Korean J Radiol 2003;4:179–83.
Yapici F, Tuygun AG, Tarhan IA, et al. Limb ischemia due to use of internal thoracic artery in coronary bypass. Asian Cardiovasc Thorac Ann 2002;10:254–55.
Bobylev D, Fleissner F, Zhang R, Haverich A, Ismail I. Arterial myocardial revascularization with right internal thoracic artery and epigastric artery in a patient with Leriche's syndrome. J Cardiothorac Surg 2013;8:53.
Biancari F, Kangasniemi OP, Mahar MA, Ylonen K. Need for late lower limb revascularization and major amputation after coronary artery bypass surgery. Eur J Vasc Endovasc Surg 2008;35:596-602.
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