LAUSR

We have read with interest the important paper published in Catheterization and Cardiovascular Interventions [1] reviewing the reported cases of left atrial appendage occlusion device thrombosis. The authors found that the mean incidence of thrombosis after closure was 3.9% for all devices. This was attributed to the presence of a high profile proximal pin connector, spontaneous contrast in the left atrial cavity, markedly enlarged atrium, high CHADS2 or CHA2DS2-VASc score, poor antithrombotic treatment compliance, or paraneoplastic syndrome. However, the development of thrombosis with such devices raises important questions regarding pathophysiology, prevention, recommendations, and treatment of thrombus formation. The Amplatzer cardiac plug is a self-expanding double-disk nitinol mesh with the two disks connected by a short waist covered by polyester fabric in order to increase occlusion. Similarly, the Watchman device has a nitinol frame and a heat-shaped knit permeable fabric. Nitinol is a nickel–titanium alloy composed of 55% nickel and 45% titanium. Nickel and polyester fabric are potential sensitizers able to produce corresponding immunoglobulin E antibodies, while titanium is no longer regarded as an inert metal. Polyesters can cause contact dermatitis [2] and foreign body reaction. Indeed, metal anions can induce hypersensitivity-associated thrombotic events via platelet FCgRI, FCgRII, FCeRI, and FCeRII receptors [3]. In the United States, nickel, chromium, and cobalt induce allergic reactions in 14%, 4%, and 9% of patients, whereas in Europe, the rates are 20%, 4%, and 7%, respectively [3]. Nitinol-induced device syndrome, resembling Kounis syndrome and chest pain was the cardinal symptom in 71% of patients who were implanted with the Amplatzer device with 70% of those patients having tested positive for nickel allergies as well [4]. Recent reports have shown that the self-expandable nitinol stents used in peripheral vascular disease and especially for occlusion of the superficial femoral artery disease have induced intractable and persistent allergic reaction that in some occasions necessitated the surgical extraction of the stent [5]. Indeed there is a small (0.28%) incidence of severe long-term problems associated with patent foramen ovale closure that might require surgical removal of the device. Thrombus following Amplatzer device insertion can be present even 5 years after implantation. Therefore, since it is not known whether device thrombosis is time-limited complication, the problem might increase and become risky if events continue to occur over time. Interventionists should pay attention to the U.S. Food and Drug Administration and manufacturer’s commercial packages that clearly state that these devices are contraindicated in metal-sensitive patients [6]. Therefore, a careful history of contraindications and hypersensitivity together with patch tests would be helpful before device implantation in susceptible patients.