Author + information
- Nicholas G. Kounis, MD, PhD∗ (, )
- Dimitrios Lianas, MD,
- George N. Kounis, MSc, MD and
- George D. Soufras, MD, PhD
- ↵∗Western Greece Highest Institute of Education and Technology, Queen Olgas Square, 7 Aratou Street, Patras 26221, Greece
We read with great interest the recent case report (1) as well as the previous 4 clinical cases reported in JACC: Cardiovascular Interventions (2) concerning very early, early, and late thrombus formation after transcatheter aortic valve replacement. These reports, in connection with other reports on subclinical leaflet thrombosis in bioprosthetic aortic valves (3), raise important questions regarding the pathophysiology, prevention, and treatment of this procedure. Different mechanisms of thrombus formation such as pertinent antithrombotic treatment, suboptimal stenting due to valve malposition, and coagulation disorders that predispose patients to thrombus formation have been proposed, and it is unlikely that valve thrombosis is caused by leaflet injury. Although stent structure and stent deployment need re-evaluation, the authors of these reports do not elaborate on the stent composition that could lead to leaflet thrombosis.
The SAPIEN bovine pericardium valve (Edwards Lifesciences, Irvine, California) has a polyethylene terephthalate skirt and a cobalt chromium stent. The CoreValve porcine pericardium valve (Medtronic, Minneapolis, Minnesota) has a nitinol (nickel-titanium alloy) stent, and the Portico bovine pericardium valve (St. Jude Medical, Minneapolis, Minnesota) also has a nitinol stent. The first of these valves is not an appropriate name because it contains nickel, titanium, molybdenum, and iron. These metals and polymer are great sensitizers that are able to produce corresponding immunoglobulin E antibodies. In the United States, nickel, chromium, and cobalt induce allergic reactions in 14%, 4%, and 9% of patients, whereas in Europe, the rates are approximately 20%, 4%, and 7%, respectively (4). Metal anions can induce Kounis hypersensitivity-associated thrombotic syndrome via platelet FCγRI, FCγRII, FCεRI, and FCεRII receptors (5).
Histological examination of a leaflet thrombus reveals the presence of many inflammatory cells within the thrombus, but a search for eosinophils and/or mast cells that denote hypersensitivity inflammation was not performed in these studies. Surprisingly, it was stated that the valve leaflet was not the culprit, and there was no indication of excessive lymphocytic infiltrate that would suggest an autoimmune rejection.
The U.S. Food and Drug Administration and manufacturers of commercial packages, however, clearly state that such stents are contraindicated in metal-sensitive patients. Therefore, a careful history of contraindications and hypersensitivity with monitoring of inflammatory mediators and lymphocyte transformation studies together with patch tests and histological examination of thrombi for eosinophils and mast cells would be helpful before stent implantation.
Please note: The authors have reported that they have no relationships relevant to the contents of this paper to disclose.
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