Fundamental principle of human biological system is to live in harmony with nature and environment.Each cell has a unique reaction when it comes into contact with external material. This reaction can be acute or chronic , local or systemic. The most severe form of allergy is called anaphylaxis that can result in instantaneous loss of life. There is a whole gamut of disorders that resulted in a separate speciality called allergic medicine .
Further ,the transplantation science have taught us an organ or cell can be rejected at any point of time after implantation (Hyperacute -chronic) .With advancement of science we have started implanting a variety of devices with complex metallurgy ,inside human body, metal clips, prosthesis, valves, wires, etc .How the body handles them .The consequences can be a mild reaction to major ones occasionally.
Consider ,a local allergy due to a orthopedic prosthesis in one of the leg bones is far less serious than a metal within a coronary artery irritating the intima .
Remember hypersensitivity reactions can be severe . This lady reacted like this to a sandal slipper -A fiery red infiltration
Imagine if a stented coronary artery react like this what would be the possible consequence ?
In susceptible individuals , can a metal cause
- Intimal hyperemia
- Intimal induration
- Intimo-medial edema following stent deployment
Why drug eluting stents are more prone for hypersensitivity ?
The answer is simple , while metal allergy is a comparatively rare phenomenon, the drugs we coat and the polymers used are many fold likely to result in hypersensitivity reaction.
While the world is worried more about penicillin , sulpha allergy which occurs in 1 in 100000 , we tend to ignore the metal and drug reactions within the tender coronary arteries.
What is the clinical expression of stent hypersensitivity ?
It is often a coronary event in the acute phase and restenosis in chronic phase.
How much of acute stent thrombosis is related to stent allergy mediated reaction ?
The exact incidence will never be known. It could be high. Whenever a sudden unexpected early stent occlusion can be a suspect .
Is stent allergy a local reaction or systemic reaction ?
It is most often local .The drugs the stent elute can elicit a systemic reaction occasionally.
So what can be done to prevent this complication ?
Drug companies in it’s package regularly include the warning message ! What does it imply to have a caution on the covers ? .This warning simply represent about our ignorance in this issue. We presume it is a minor problem.
Questions unanswered
- How does a cardiac patient knows whether he is hypersensitive to stainless steel or nickel ?
- Is it practical to have a stent allergic test in every patient before PCI ?
- Is routine administration of corticosteroids for few days after PCI an answer ?
Reference
Dr.S.Venkatesan MD 