English subtitles for clip: File:Arteriovenous malformation video.webm
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1 00:00:05,109 --> 00:00:08,860 Arterio refers to the arteries, which are the the blood vessels that take blood away 2 00:00:08,860 --> 00:00:14,599 from the heart, and venous refers to the veins, which carry blood toward the heart. 3 00:00:14,599 --> 00:00:21,200 Mal- means “badly”, so an arteriovenous malformation, or AVM, is some sort of “bad” 4 00:00:21,200 --> 00:00:25,110 or abnormal formation between the arteries and veins. 5 00:00:25,110 --> 00:00:30,150 Typically, oxygen-rich blood is carried to the body’s tissues via arteries. 6 00:00:30,150 --> 00:00:35,280 Large arteries split into smaller and smaller arteries, and feed into capillary beds, where 7 00:00:35,280 --> 00:00:38,890 cells exchange oxygen for carbon dioxide. 8 00:00:38,890 --> 00:00:43,050 The capillaries then feed into larger and larger veins, which carry deoxygenated blood 9 00:00:43,050 --> 00:00:45,079 away from the tissues. 10 00:00:45,079 --> 00:00:49,770 Normally, arterial blood is under a high-pressure system, and as it goes through smaller and 11 00:00:49,770 --> 00:00:55,050 smaller vessels, ultimately into the capillary bed, pressure in the vessels becomes significantly 12 00:00:55,050 --> 00:00:59,280 lower, and blood drains into the lower pressure systemic veins. 13 00:00:59,280 --> 00:01:03,920 So this capillary bed dampens the arterial flow a bit. 14 00:01:03,920 --> 00:01:09,140 With AVM, this whole capillary bed isn’t there, and a group of arteries directly link 15 00:01:09,140 --> 00:01:11,990 up with a group of veins instead. 16 00:01:11,990 --> 00:01:16,340 The vessels in the AVM can start to tangle up and are called a nidus, which is Latin 17 00:01:16,340 --> 00:01:18,540 for “nest”. 18 00:01:18,540 --> 00:01:22,520 When a single artery and a single vein link up abnormally like this, it’s called an 19 00:01:22,520 --> 00:01:26,170 arteriovenous fistula. 20 00:01:26,170 --> 00:01:30,920 In AVM the arteries and the veins are under high systolic blood pressures because there 21 00:01:30,920 --> 00:01:35,380 are no capillaries to dampen the pressure, which means that the AVM can expand in size 22 00:01:35,380 --> 00:01:39,320 over time and can put pressure on the surrounding tissue. 23 00:01:39,320 --> 00:01:43,409 This pressure on surrounding capillaries can pinch them shut and prevent that functional 24 00:01:43,409 --> 00:01:45,939 tissue from getting blood flow. 25 00:01:45,939 --> 00:01:51,040 Also, the high pressure causes the arteries supplying blood to dilate, while the veins 26 00:01:51,040 --> 00:01:54,479 thicken and undergo fibrosis. 27 00:01:54,479 --> 00:01:59,040 Vessel walls are also prone to forming aneurysms, which are these balloon-like protrusions; 28 00:01:59,040 --> 00:02:03,240 and because the vessel walls are weakened and stretched out, they are also at risk for 29 00:02:03,240 --> 00:02:05,030 ripping and tearing. 30 00:02:05,030 --> 00:02:10,959 Although AVMs can form anywhere in the body, they most often form in certain parts of the 31 00:02:10,959 --> 00:02:15,240 body like the brain, spinal cord, and also the lungs. 32 00:02:15,240 --> 00:02:20,590 If the AVM ruptures in the brain, blood escapes into the surrounding brain tissue. 33 00:02:20,590 --> 00:02:24,480 Sometimes the blood-loss can be small, called a microbleed, which doesn’t typically cause 34 00:02:24,480 --> 00:02:29,540 much damage, but sometimes the blood loss is severe enough, people might experience 35 00:02:29,540 --> 00:02:33,730 what is called an intracerebral or subarachnoid hemorrhage. 36 00:02:33,730 --> 00:02:37,569 Depending on the location, this can cause several neurological complications like headaches 37 00:02:37,569 --> 00:02:41,430 or seizures, as well as other neurological symptoms that can relate to the part of the 38 00:02:41,430 --> 00:02:46,760 brain affected—like for example, if it affects the hippocampus, it might affect the person’s 39 00:02:46,760 --> 00:02:52,060 memory, or if it’s the basal ganglia, it might affect their ability to move. 40 00:02:52,060 --> 00:02:57,940 In the spinal cord, AVMs can, by the same mechanisms, damaged nerve fibers, which can 41 00:02:57,940 --> 00:03:02,420 cause sensory disturbances, muscle weakness, or even paralysis in the parts of the body 42 00:03:02,420 --> 00:03:05,569 controlled by the affected nerves. 43 00:03:05,569 --> 00:03:10,250 In the lungs, an AVM might result in shortness of breath or coughing up blood. 44 00:03:10,250 --> 00:03:15,110 It’s also important to remember that having blood flow out of the heart to an artery, 45 00:03:15,110 --> 00:03:19,940 then through the AVM to a vein, and directly back to the heart is a lot of wasted work, 46 00:03:19,940 --> 00:03:24,560 since that oxygen’s not going to the tissue’s capillaries like it should and it’s just 47 00:03:24,560 --> 00:03:29,150 rerouting back to the heart, which ultimately causes the heart to work harder, and over 48 00:03:29,150 --> 00:03:33,519 time, an AVM can contribute to heart failure because the heart’s doing extra work with 49 00:03:33,519 --> 00:03:36,019 each beat. 50 00:03:36,019 --> 00:03:40,879 Diagnosis might involve several imaging techniques, one of which is angiography, which is actually 51 00:03:40,879 --> 00:03:45,710 the gold standard, as well as CT and MRI. 52 00:03:45,710 --> 00:03:50,790 Aside from imaging, a distinctive clinical sign of AVM is a bruit, which is French for 53 00:03:50,790 --> 00:03:52,290 “noise”. 54 00:03:52,290 --> 00:03:57,739 When blood flows rapidly flow of blood through the AVM, it causes a whooshing noise. 55 00:03:57,739 --> 00:04:01,840 Sometimes this noise can get so loud, especially if the AVM is in the brain, that the person 56 00:04:01,840 --> 00:04:06,650 can hear it themselves, which can cause serious psychological stress, not to mention making 57 00:04:06,650 --> 00:04:08,849 it hard to sleep or hear other things. 58 00:04:08,849 --> 00:04:14,020 The cause of AVMs isn’t well understood, although it’s thought to be congenital and 59 00:04:14,020 --> 00:04:18,990 caused by some mistake in blood vessel growth during embryonic or fetal development, some 60 00:04:18,990 --> 00:04:21,320 of which seems to be genetic. 61 00:04:21,320 --> 00:04:26,599 One well known relationship is with Osler-Weber-Rendu disease which is an autosomal dominant disorder 62 00:04:26,599 --> 00:04:30,930 that causes problems with blood vessels throughout the body. 63 00:04:30,930 --> 00:04:35,680 Most AVMs are treated even if the person’s not symptomatic, because of the risk of complications, 64 00:04:35,680 --> 00:04:37,610 like bleeding. 65 00:04:37,610 --> 00:04:42,110 Medications can be used to treat symptoms from an AVM like headaches. 66 00:04:42,110 --> 00:04:46,309 But also they might also have certain procedures, like radiosurgery, where beams of radiation 67 00:04:46,309 --> 00:04:51,379 are targeted at the AVM, causing the vessels to scar and close off. 68 00:04:51,379 --> 00:04:57,749 Or they might have endovascular embolization, where a catheter is used to obstruct the vessels. 69 00:04:57,749 --> 00:05:01,900 Because the location of the AVM varies so widely, usually the procedure varies on a 70 00:05:01,900 --> 00:05:14,490 case-by-case basis.