| Affiliation |
(AGL) Chairman, Department of Ophthalmology, The Methodist Hospital, Houston, Texas; Professor of Ophthalmology, Weill Cornell Medicine, New York City, New York; (SD) Class of 2023, Baylor College of Medicine, Houston, Texas |
| Transcript |
Today we're going to be talking about the subclavian steal syndrome in neuro-ophthalmology. And the subclavian artery, as you know, is under the clavicle. And so, you need to know a little bit about the anatomy of the aorta. So, the right side branches are different than the left side. So, on the right side we have the no-name branch, the innominate, sometimes called the brachiocephalic, because it goes to the arm, the subclavian, and also to the cephalic, the head, through the common carotid and then the internal carotid. And the vertebral artery take-off is from the right subclavian. And this is called the innominate. And this is the internal carotid artery coming off the common carotid artery. And then on the left side, it's a little bit different. The left common carotid to the left internal carotid artery. And on the left side, the left-sided subclavian and the vertebral artery take off. And so, you need to know a little bit about how this anatomy affects us, because in addition to the normal things where aortic disease can throw emboli either from the valve or from atherosclerotic plaque into the anterior circulation (into the carotid) or into the posterior circulation (through the vertebral arteries); so there are both afferent and efferent complaints. So, the most common would be, of course, unilateral vision loss from amaurosis fugax, or an embolus flying into your eye, a branch retinal artery occlusion, or a central retinal artery occlusion can occur in the anterior circulation. And in the posterior circulation, the vertebral arteries, that's going to cause dizziness, diplopia, drop attacks, syncopal episodes, lower cranial neuropathies, dysarthria, dysphagia; or it might fly up into the basilar through the vertebral and end up in the posterior cerebral artery and cause a homonymous hemianopsia or cortical visual loss, and of course the Wallenberg syndrome. The vertebral artery can supply the PICA, the posterior inferior cerebellar artery, and lead to the lateral medullary syndrome. So, all of those can come to us, and so we're not really going to be talking about that as much as the steal itself. So, because you can have an occlusion or stenosis at the proximal subclavian artery- so we are here in the left side- if you use your arm, that will increase the demand to go to the arm. And because this is a flow directed, pressure directed flow, the vertebral artery flow can go the wrong direction to supply the demand increase in the arm. And so, the subclavian can steal blood from the vertebral artery, and that can cause transient ischemia in the vertebral-basilar distribution (vertebral-basilarin sufficiency). And the same thing can happen on the right side where the vertebral flow which used to be anterograde is now reversing retrograde to make up for increased demand in the limb. There's a different version of this, however that is way rarer, that I want you to know about, which is sometimes the internal mammary artery, in this case the left internal mammary artery. It's being used by our colleagues in cardiovascular surgery to reperfuse the heart. So, they might be using this LIMA as a bypass graft to the coronary arteries, so that as you know is called a coronary artery bypass graft- where we're bypassing the obstruction in the coronary system by hooking up a graft, in this case from the left internal mammary artery. And what that means is, sometimes the subclavian has an occlusion and is now not stealing from the vertebral artery but is stealing from your heart: a coronary artery steal syndrome- where the subclavian demand is now driving the blood flow from the left internal mammary artery and that's stealing directly from your coronary artery. And so, these patients sometimes have chest pain induced by using their arm, and that is a very uncommon version of the subclavian steal syndrome created by the graft, the coronary artery bypass graft, compounded by a proximal stenosis or occlusion in the subclavian artery. So instead of a vertebral retrograde flow, we are having retrograde flow from the LIMA and that's stealing from your heart. And the reason that's important is that can lead to myocardial ischemia and cause a decrease in cardiac output which could cause a pre-existing stenosis in any of the other great vessels to become symptomatic and that can produce amaurosis fugax on the same side, on the opposite side, in the anterior circulation, or the posterior circulation, because the problem is now cardiac in origin rather than the subclavian itself. So, you need to know a little bit about the steal. The subclavian is doing the stealing, and it can steal from the vertebral; or if you've had a coronary bypass graft, from the graft itself, the LIMA. |
