Dipyridamole, a non-nitrate coronary vasodilator that also inhibits platelet aggregation, is combined with other anticoagulant drugs, such as warfarin, to prevent thrombosis in patients with valvular or vascular disorders. Dipyridamole is also used in myocardial perfusion imaging, as an antiplatelet agent, and in combination with aspirin for stroke prophylaxis.
In this video i’ll be talking about dipyridamole and how dipyridamole is used in cardiac stress test how it inhibits thrombin formation and i will also discuss how exactly it is useful with an example how dipredamol is very very important when we are talking about cardiac stress test so let’s get right into it starting with the mechanism of action so let’s
Imagine that this is our thrombin now we already talked about that dipyridamole is a thrombin inhibitor it inhibits thrombin by the way thrombin is formed by the enzyme thromboxane synthase this enzyme is inhibited by dipyridamole now because dipredamol is a thromboxane synthase inhibitor there is going to be less thromboxane a2 what is the different functions
In thromboxane a2 i always get confused with thromboxine and prostaglandins so i came up with a way of remembering what exactly thromboxin a2 does now see how the x is like this okay it’s like constricting right so thromboxane a2 is responsible for bronchoconstriction vasoconstriction and platelet aggregation it’s kind of bringing everything together in the
Middle right bronchoconstriction which is going to constrict we can see how the x is responsible for the constrict vasoconstrict the same thing and platelet aggregation so because dipyridamole is a thromboxane synthase inhibitor it is also going to inhibit thrombin formation and we are going to have less thromboxane available in our body and what is thumboxin
Responsible for it is responsible for bronchoconstriction vasoconstriction and platelet aggregation now this is only one of the many functions of dipyridamole this would be number one what would it be number two from a dipyridamole also inhibits adenosine deaminase how is that in how is that going to do anything now adenosine is converted to ionosine by
Adenosine deaminase and this is inhibited by dipyridamole now along with inhibiting adenosine deaminy dipyridamole also inhibits reuptake of adenosine into platelets it is going to increase levels of adenosine obviously because adenosine is not being broken down and it will it will decrease reuptake of endothelin cells okay so function number one it inhibits
Thromboxine synthase it’s a thromboxane synthesis inhibitor function number two it inhibits uh adenosine deaminase which is going to increase the concentration of adenosine because adenosine is broken down to ionosine through adenosine deaminase there are more functions or mechanism of action of dipyridamole the next is adenosine deaminase is going to increase
Level of camp and cgmp and what it does is increase camp is actually going to inhibit um it’s going to inhibit formation of adp it’s going to inhibit adp to form platelets okay this is going to be inhibited through the action of cgmp dipyridamole along with cgmp is going to increase the effect of no and cause vasodilation okay so that’s the function of
Dipyrademol in terms of camp and cgmp so now that we understand the concept behind dipyridamole let’s see if we can understand an example and get a little bit of further idea of how exactly it is useful in cardiac stress test now we’re going to do that with this with this question so the question says in which of the following circumstances stress tests might
Underestimate the degree of ischemic tissue by the way we’re using dipredamol as the cardiac stress test drug now in which of the following circumstances stress tests might underestimate the degree of ischemic tissue where is it going to underestimate the degree of ischemia is it going to be bradycardia or three vessel high-grade obstruction left bundle branch
Block osteoarthritis or right coronary artery 99 percent occlusion so in order to understand exactly what happens we have to understand the mechanism of action of diplodol and how and why we use it in cardiac stress test so let’s say this is a coronary artery and this is a coronary artery and let’s say the coronary artery vessels are like so now see how this
These are thinner and these are much thicker the reason for that is because this is pre diperydemal okay so in an in a in a cardiac coronary vessel when there is no dipyridamole the vessels pre-stenotic and postenantic are always vasodilated and that’s because we want to get as much blood through the stenosis as possible which is not going to happen with this
Vessel because we’re not trying to push blood through so these vessels are just going to be normal or not vasoconstricted but normal not visibility what happens if we give diapered amounts so let’s imagine post dipyridamole post diapering what happens is these vessels are going to vasodilate now okay and they’re going to be vasodilated as a result now both the
Coronary vessels are going to be visible dilated now what dipyridamol does is through this vasodilation we can compare the blood flow through this and through this and we can see where the ischemia lies kind of even through a cardiac stress test so that is exactly why we use dipyridamole okay now let’s do the question now so the question says again in which of the
Following circumstances stress tests might underestimate degree of ischemic tissue so where are we going to underestimate that there is ischemia that is the question is it going to be bradycardia bradycardia and diapery devil has no relationship so no what about three vessel high grade obstruction three vessel high grade obstruction three vessels are obstructed
Interesting high grade obstructions it’s highly obstructed now don’t we want to compare obstructed versus non-obstructed if three vessels are obstructed then we’re not really gonna be able to know that there is obstruction we might think this is normal right normally this is how much blood is going through because most of our vessels are obstructed so we might
Underestimate that there is an ischemic tissue if there’s three vessel obstruction so this could be a possible answer what about left bundle branch block with left bundle branch block what is the relationship with coronary artery and left bundled branch block not i mean we there is no direct correlation so that is also out osteoarthritis also out for the same
Reason that it’s not directly correlated what about right coronary artery 99 percent occlusion if it is 99 occluded no blood will pass through yes it will we will be able to compare ischemic versus non-ischemic that is true but this even though this is relevant with dipredamol and yes if someone has 99 percent occlusion we will do a diaper democratic stress
Test and we will find out but the question is not that the question is asking asking which one are we going to underestimate that means we will not be able to find out that there is ischemia with only right coronary artery obstructed or occluded we will pick that up right away because it’s only one artery that’s obstructed if we pass blood through the other artery
Through visibility we’ll know that there is more blood going through and you know that is that the right coronary artery is obstructed but in choice b since three vessels are obstructed at the same time we will not be able to distinguish which one is obstructed and which is which one is not obstructed and we will not be able to find out that there is ischemia
With three vessel obstruction okay so in this case the answer is going to be b
Transcribed from video
Dipyridamole By Dr Aishwarya Kelkar Medical Lectures