Collateral Circulations

00:01 An important concept in terms of the organization of the vasculature: there is a collateral circulation in many of the organs.

00:10 What do I mean by collateral circulation? Well, here we're looking at a heart that has been permeabilized with metal salicylates.

00:19 So I can see through the heart.

00:21 I've injected the coronaries, with a latex or red latex to highlight the vasculature coming onto the surface of the heart.

00:30 So, that first vessel that you see in front that's left anterior descending.

00:35 And it branches, and branches, and branches into a fine capillary network.

00:40 Over here, we have the right coronary artery, the RCA.

00:43 And again, it comes off the aorta and branches, and branches, and branches into a fine capillary network.

00:48 And finally, we have the left circumflex artery.

00:52 Same general organization in terms of branching into a fine capillary network.

00:57 Now, there is a space or a region in the heart between these major vessel territories where the blood kind of comes in from both sides.

01:07 And when it comes in from both sides, We have an area or a territory that is getting a collateral circulation.

01:15 So shown here is the watershed area between the left anterior descending and the left circumflex artery.

01:23 This is where the branching of the left anterior descending —the fine capillary network— meets the fine capillary network from the left circumflex artery.

01:31 And that zone is potentially at risk if we block both vessels.

01:36 However, if I only block one, say I block the left anterior descending, in many cases, the left circumflex can now perfuse that zone by a collateral supply.

01:49 It's kind of a nice organization.

01:51 There's another one.

01:53 Another watershed zone between the right coronary artery and the left anterior descending another watershed zone.

01:58 Well, they're not just watershed zones in the heart.

02:01 They're watershed zones in many other places within the body, like the brain.

02:07 In fact, because certain organs are really, really, really important, like the heart and the brain, they tend to have a vasculature that has collateral circulations.

02:18 Turns out, kidneys don't really have a good collateral circulation, Saying, there is, they're not as important.

02:24 No, they're important.

02:25 But they don't have a collateral circulation.

02:28 Alright, let's look at the brain.

02:29 So we have a central circle, Circle of Willis, where many blood vessels come in, but that means that as we bring blood in, it can be distributed anywhere around that circle, so it provides a terrific collateral circulation.

02:44 There's the basilar artery, coming up from the base of the brain.

02:51 Vertebral arteries that coalesce to form the basilar artery.

02:55 We have the posterior communicating arteries, the anterior cerebral artery, the anterior communicating artery, the middle cerebral artery, all of these are feeding into the Circle of Willis and we can have blood supply from almost any of those be able to perfuse the entire circuit.

03:17 In case one of the vessels is not working appropriately.

03:22 All this is coming up from the internal carotid arteries.

03:25 And they branches into the various elements that we see in there.

03:29 Okay, so there are watershed areas in the brain.

03:32 And this is just between the various circulations.

03:35 Okay, kind of makes sense now, hopefully.

03:38 This is just showing you the kind of in a schematic form what that collateral circulation looks like.

03:46 So up top, on the left hand side, we have the border zone between the anterior cerebral artery and the middle cerebral artery.

03:54 And if we have loss of blood flow to both of those, we're in trouble.

03:58 But if we have loss of blood flow to only one collateral circulation will tend to keep the tissues alive.

04:05 In the middle, is the internal border zone Again, if both of those arteries are blocked, we're in trouble.

04:12 And Circle of Willis may help us a little bit, but maybe not entirely.

04:18 And finally, there is another border zone between the middle cerebral artery, and the posterior cerebral artery.

04:24 So the brain is a bit over-engineered because we need to protect it.

04:28 We don't want to have strokes.

04:31 And there are collateral circulations in other areas within the body.

04:34 So this is just looking at the collateral circulation between the superior mesenteric artery and the inferior mesenteric artery demonstrating the watershed zone that happens in the area shown here