Peripheral Artery Disease: Pathogenesis

00:01 The pathogenesis is as we have been talking about due to artherosclerosis. What happens is artherosclerosis develops slowly narrowing the blood vessel. It can also develop because the atherosclerotic plaque ruptures and a blood clot forms and pieces of blood clot can embolize down into the smaller arteries of the leg causing gangrene or the blood clot can come from further up in the arterial system. It can come from a blood clot over an atherosclerotic plaque in the aorta. It can come from a blood clot actually in the heart. It can come when the patient has a heart attack. A blood clot may form inside the heart and embolize and travel down and cause a sudden arterial occlusion particularly in an area that has already been narrowed by atherosclerosis. The arterial emboli as then I have said once more can occur in the left atrium from atrial fibrillation and the carditis or infection in the heart valves, sometimes will have blood clot overlying the infected valve that can embolize and of course artificial heart valves can form a blood clot that can embolize as well.

01:21 Artherosclerosis in the aorta and other major arteries are very common source of ruptured plaque with the blood clots that embolises and of course these emboli don’t have to go to the legs. They can also go to the carotid arteries and cause a stroke.

01:38 Atrial fibrillation, let's take a few minutes to talk about it because atrial fibrillation is extremely common. Remember what atrial fibrillation is. The heart beats in a nice normal fashion like this papump, papump, papump. In atrial fibrillation, the atrium no longer is working in a coordinated fashion but in a very irregular way like this…and passing many many electrical impulses down into the ventricle only some of which gets through.

02:08 So instead of a nice regular pulse pum, pum, pum you have this pum, papapum, pumpapapum, papapup… very irregular. When that happens in the atrium, the disorganized atrial activity increases the likelihood that a blood clot will form in the atrium and if it breaks off and embolises and goes to the brain it can cause a stroke. In fact 15% to 20% of all strokes in the United States are due to embolization from a blood clot in the left atrium that is the result of atrial fibrillation. AF increases the risk of stroke by 4 to 5 fold. It's an independent risk factor for ischemic stroke severity and recurrence. In other words because the arteries have not been prepared with collateral circulation when the embolus arrives, usually a very healthy piece of the brain is deprived of blood flow and dies forming a stroke.

03:13 So the stroke risk unfortunately occurs even if people don’t have any symptoms from their atrial fibrillation or even if they only occasionally have atrial fibrillation and go back and forth between the normal rhythm and atrial fibrillation. And so the term often used by the doctors is cardioembolic stroke. That is, it is an embolism that comes from the heart passes out into the circulation and unfortunately goes to the brain. Now why would it go to the brain? Why doesn’t it go elsewhere? Why doesn’t it go to the kidneys or elsewhere? Sometimes it does, but it turns out that 25%, fully a quarter of the blood flow that is coming out of the heart goes to the brain. So the brain gets a lot of the blood flow so it also has a much higher chance of getting the blood clot that is coming out of the heart.

04:06 Now you can also have strokes because of artherosclerosis, the narrowing in the blood vessels that we talked about before that can lead to a heart attack. The atherosclerotic plaque can rupture, a blood clot can form and the artery can be completely occluded, or the plaque can rupture, a blood clot forms and a chunk of the blood clot embolises up to the brain not from the left atrium in this case but from a ruptured atherosclerotic plaque in the carotid artery.

04:37 So narrowing or constriction of the carotid arteries is a major cause of strokes and about 25% of all strokes are caused by carotid artery artherosclerosis. As I said it can be due to embolization or to complete occlusion relating to rupture of one of these atherosclerotic plaques. Detection of the asymptomatic carotid plaque is very poor by physical exam. You might hear a bruit, that is you might hear a sound over the artery, reflecting turbulent blood flow in the carotid artery but very often you don’t hear anything so the only way to make this diagnosis is usually with a non-invasive test that is with an ultrasound test that shows you the atherosclerotic plaque. So peripheral artery disease whether it is