What are our risk factors?
There’s risk factors for myocardial ischemia
so if you’ve ever had a heart attack before,
that puts you at risk for mesenteric arterial embolism.
If you have a history of endocarditis,
part of the endocarditis that’s attached to the valve
can go ahead and cause the clot to go to the mesenteric vessels.
A ventricular aneurysm can cause a blood clot as well,
so if you have an aneurysm and the blood kind of just sits there
in that aneurysmal component of the ventricle of the heart,
that can lead to the blood clot going to the vessels
and then atrial dysrhythmias.
So does the patient have atrial fibrillation?
Which can go ahead and lead to the blood clots
going to the mesenteric vessels as well.
Now, the most frequent vessel involved in mesenteric arterial embolism
is the SMA, the superior mesenteric artery.
Clots when they go here, they lodge generally distally
and when the SMA is affected,
the jejunum which is the second portion of the small intestine
is the most commonly affected portion of the small intestine.
It’s important to note that the SMA is the furthest vessel from the collaterals.
So patients who have a problem with their SMA,
you’re not gonna be getting blood flow from lots of other areas.
So sometimes if you have an occlusion of another one of the blood vessels,
there’s a lot of collateral flow.
There’s a lot of other backup flow that can help supply those areas
but the SMA doesn’t necessarily have that.
Secondly, we can talk about mesenteric arterial thrombus.
Now, this is one of the second causes for mesenteric ischemia.
This is due to atherosclerotic disease.
So the patient has plaque buildup, cholesterol buildup,
in the mesenteric vasculature.
These are more commonly related to chronic mesenteric ischemia.
So while mesenteric arterial embolism is an acute process.
That’s a process where you have a blood clot,
it goes to a mesenteric vessel, it causes acute decrease in blood supply,
this is more of a chronic problem.
The occlusion here is more commonly at the proximal superior mesenteric artery
rather than the distal in the mesenteric arterial embolus.
What are the risk factors here?
Very similar to risk factors for patients who are having myocardial ischemia,
for patients who have underlying heart disease,
underlying peripheral arterial disease, diabetes is a big risk factor,
chronically elevated blood pressure, smoking, and elevated cholesterol.
So if a patient has a lot of these risk factors
and risk factors for heart disease,
that’s something that’s gonna predispose them to a mesenteric arterial thrombus.
The third cause here is non-occlusive mesenteric ischemia.
Non-occlusive mesenteric ischemia is kind of just what it sounds like.
It’s due to vasospasm of the mesenteric vessels.
So patients who have a spasm of the vessel,
there’s not gonna be a good blood flow that goes through there.
This can result in a recurrent and repetitive injury for those patients
because it might be a recurrent issue,
so they might have vasospasm that may get better,
then it may get worse again, then it may get better again.
In this situation, it’s different than the prior two things we discussed
in the sense there’s nothing actually blocking the vessel.
This is non-occlusive.
The risk factors here are hypoperfusion, so patients who are hypotensive,
patients who are septic, can have hypoperfusion.
They cannot get enough blood flow that’s gonna those blood vessels.
So sepsis, hypovolemia, patients who are very dehydrated,
hemorrhagic shock in the situation of trauma
or someone that’s had a massive GI bleed,
and then pancreatitis is the other condition
that can sometimes lead to decreased blood flow in those mesenteric vessels.
Nervous system activity can sometimes also cause vasospasm to those vessels,
and primarily, these are things that increased the sympathetic nervous system activity.
So CHF is one, vasopressors, so sometimes this is iatrogenic,
sometimes this is due to medications that we give people.
So if someone comes in and they’re very hypotensive,
their blood pressure is low,
we give them medicine to support their blood pressure,
sometimes, those medicines can do too good of a job constricting the vessels,
and can cause decreased blood flow to the intestines.
And then cocaine is an illicit drug that can cause increased sympathetic stimulation
and primarily would cause vasospasm,
so it would cause those vessels to clamp down inappropriately.
And last but not least, we have mesenteric venous thrombosis.
This is the least common cause of mesenteric ischemia
making up about 5 to 15 % of cases.
Most commonly, it involves the superior mesenteric vein.
So this is a problem with the venous system rather than the arterial system.
Oftentimes, there is an underlying thrombotic disorder
or a hypercoagulable state that the patient may or may not know about yet.
Young women who are on oral contraceptive agents,
especially oral contraceptive agents
that contain estrogen can predispose to clotting.
If there is venous stasis, so the blood is kind of just sitting around there
in portal hypertension in a portal system,
that can be a risk factor, and then Virchow’s triad,
Virchow’s triad is basically immobility damage to the blood vessel
and that can predispose to clotting as well.