Today’s video is on the subject of intracoronary stents. In this video, I will talk about what stents are, why they are used and what benefits and risks are associated with their implantation.
The first thing to understand is that for most of us, as we get older, the major risk to our health will be progressive ‘wear and tear’ in our heart arteries (coronary arteries). There are 2 problems with this process. The first is that as the ‘wear and tear’ progresses, there will be progressive narrowing of parts of the heart arteries which then means that it becomes more difficult for the blood to get to where it is needed especially at times of increased demand and therefore the muscle cells which need the increased amount of blood would suffocate and thereby manifest with symptoms of chest discomfort or breathlessness. This is called stable angina.
The second problem with ‘wear and tear’ is that the vessel becomes more prone to blood clots forming acutely within the blood vessel and very suddenly a blood clot can block the vessel causing acute suffocation of the heart muscle. This is called unstable angina or a heart attack.
In the old days, the only way to treat angina was either using medications or open heart surgery. Whilst medications were able to reduce the demand of the heart or transiently open these blood vessels thereby relieving symptoms they did not really fix the narrowing.
Surgery on the other hand was a major undertaking with the need to cut the chest open under a general anaesthetic. The surgeon would then have to take another blood vessel from the leg to attach onto either side of the narrowed blood vessel to bypass the narrowing. Not every patient was fit enough to undergo surgery and there was a limitation in that the narrowing had to be in a vessel big enough for the surgeon to be able to stitch the bypass onto.
GIven these limitations, scientists became increasingly interested in seeing if there was a way of accessing the narrowed blood vessels without the need for open heart surgery. The breakthrough came in 1953 when a Swedish radiologist, Dr Sven Ivar Seldinger developed the Seldinger technique which made it possible to access internal blood vessels by puncturing a blood vessel which was externally visible. The idea was that if one could puncture an artery in the wrist or the groin then you could introduce a thin wire through the needle and then use x-ray guidance to move it all the way up to the heart and then cannulate the coronary arteries. If you could then slide a tube up the wire and remove the wire, you could inject radiopaque dye into the blood vessels and take x-rays and identify the location of the narrowings. That procedure was called angiography.
Once doctors became comfortable with the practice of angiography, the next challenge and goal was to develop a way of using the same method to deliver an intervention to open up the narrowing. In 1977, a German cardiologist, Dr Andreas Gruendzig was able to perform the first angioplasty where he was able to access the narrowings and then use a balloon at the end of a catheter to stretch open the narrowing with excellent results.
This was obviously a huge breakthrough and doctors started developing experience and expertise in this technique which was called balloon angioplasty. As more procedures were done and research on long term outcomes started becoming available, it became apparent that up to 30% of patients would re-develop symptoms due to a re-narrowing (restenosis) within the blood vessel that had undergone the balloon angioplasty and therefore needed a repeat procedure. This was thought to be due to 3 factors:
- Acute recoil of the stretched segment.
- Negative remodelling of the stretched segment
- Growth of tissue within the stretched segment
To try and improve on this, scientists became interested in the idea of developing a stent which could then be implanted within the narrowing and this would then hold the vessel open and reduce the risk of restenosis by reducing the chances of recoil and this negative remodelling. Growth of tissue within the stent would still be feasible. This led to the development of the 1st generation of intracoronary stents (now called Bare Metal stents) and it was noted that indeed the bare metal stents were twice as effective as balloon angioplasty in terms of reduced risks of restenosis. However despite this improvement, upto 15% of patients would still develop restenosis within a year presumably because of growth of tissue within the stent.
To try and reduce this risk of restenosis, Scientists found that if they could coat the stent with a medication which is released over a few months (between 2-12 weeks) then that could reduce proliferation of cells which could in turn reduce the risk of restenosis. This led to the development of what are now known as Drug-eluting stents (DES). These stents tend to be coated with a type of antibiotic and antiproliferative agent which prevent new growth within the lumen of the stent. Whilst these stents were significantly more effective at preventing new growth of abnormal tissue and reduced the risk of restenosis by about 50%, the problem was that they were so good that they would not allow the patients normal tissue to embed the stent and therefore a significant paramount of the foreign surface of the stent remain uncovered and this then acted as surface where blood could clot and it became apparent that there was a significantly higher risk of sudden blood clots forming and blocking the stent off and this was termed late stent thrombosis. This was a potentially catastrophic complication as the patient would be asymptomatic and then suddenly out of the blue have a major heart attack. With further advancements, stents design has become a lot more sophisticated and now stent thrombosis has become an uncommon problem. Iis nevertheless still a potentially dangerous complication. Whilst the prevalence of stent thrombosis is 1-2%, the mortality rates can be as high as 20-40%.
And it is for this reason, that it is recommended that after a stenting procedure, patients are recommended to take medications that reduce the risk of thrombosis which appears to be significant in the first year and perhaps greatest in the first 6 months. The medications that are recommended are a combination of 2 antiplatelet agents – one of which is Aspirin and the second is either a medication called Clopidogrel, Ticagrelor or prasugrel. Whilst for several years we have used clopidogrel as the second agent, its use especially in people who have had a recent heart attack has been surpassed by Ticagrelor or prasugrel and it is generally recommended that these medications be continued in combination for a full year after the implantation of the stent. The problem with taking 2 antiplatelet agents is the enhanced risk of bleeding but it is felt that the risk of blood clots in most patients is higher than the risk of bleeding especially within the first year. By the end of the year the risk of stent thrombosis has probably fallen to the point that the risk of bleeding is considered to be greater than the risk of thrombosis and therefore the second antiplatelet is usually discontinued by the end of the year. It is important to understand however that whilst a lot of what we recommend is based around reducing the risk of stents blocking off, there is another advantage to having the 2 agents in combination and that is they also reduce the risk of blood clots forming in the non stented vessels and therefore apart from just preventing the stent blocking, they may also reduce the risk of more heart attacks in non stented vessels. It is believed that the group of patients who are at a highest risk of further heart attacks are diabetics, patients who have kidney disease, peripheral vascular disease and those who have disease in more than on coronary artery – and there was a study called PEGASUS-TIMI 54 which suggested that in these patients it was better for them to continue on a combination of 2 antiplatelets (albeit at a lower dose) for a further 1-3 years after their index heart attack.
There have been a bunch of studies looking at the risk of stent blockages in patients who have prematurely discontinued the second antiplatelet agent and we have observed that more than 25% of patients who stop their clopidogrel in the first month will suffer a stent thrombosis. Premature stopping of the clopidogrel is associated with a 30 fold increased risk of stent thrombosis and in another study of 500 patients, 7.5% died within the first 11 months if they stopped their second agent compared to only 0.7% who did not stop.
In summary, stents have revolutionised how we treat heart artery narrowings and blockages. They have markedly reduced our reliance on open heart surgery which was really the only option (other than pills) in the last century. Stents however carry their own problems and the most important being that they are a foreign body and can block off. In that sense, cultivating a healthy lifestyle and complying religiously with the 2 antiplatelet medications that are usually recommended for at least a year after the stent is crucial
I hope you found this video useful and I would love to hear your thoughts.