Coronary stents are small tubes inserted into narrowed or weakened arteries in order to help improve blood flow to the heart. Rajiv Gulati, M.D., Ph.D., an interventional cardiologist at Mayo Clinic in Rochester, Minn., explains:
"Most interventional cardiologists will, at some stage, have to decide whether to place a coronary stent in a patient with a history of skin allergy to one of metal components, most commonly nickel.
Our study found no evidence of an increased risk of heart attack, death, or restenosis, which is a recurrent narrowing within a stent, in patients who reported themselves to be allergic to metal prior to implantation.
These findings should provide some reassurance to clinicians and patients who are faced with this clinical issue, especially as there has been scarce and conflicting information in the literature."
The team assessed early and long-term clinical outcomes in 29 patients with a history of metal allergy who underwent coronary stent implantation, and compared them to 250 nonallergic patients.
Between the two groups, the researchers found no considerable differences in the rates of repeat revascularization of the originally treated coronary artery, heart attack or death at 30 days and 4 years.
After examining markers of an allergic response before and after implantation, the researchers discovered that eosinophil, white blood cell, and lymphocyte counts did not alter after implantation. According to the researchers, results of the study indicate that stent implantation is safe in patients allergic to metal components and cardiologists need not worry about systemic immune reaction.
According to Dr. Gulati, although earlier investigations have analyzed metal allergy and stent placement, they focused primarily on the risk of restenosis. In addition, these studies had some limitations in design and produced conflicting results.
Since 1997, coronary stents in the U.S. have been constructed using 316L stainless steel, cobalt-chromium alloy, or platinum-chromium alloy platforms. All stents contain between 10% to 35% of nickel and chromium as chromate (18% to 20%).
Approximately 8% of the population have nickle allergies. Although nickle allergies are one of the most prevalent causes of allergic contact dermatitis, they are more common in women and are often triggered by nickel-containing jewelry, such as earrings or body piercings.
Skin rash, dry patches, redness or itching within 12 to 48 hours, after initial contact with the metal, are usually reported by individuals with known or suspected skin allergy.
In this study, the researchers found that hypersensitivity to chromium was reported in 9 of 29 cases and to nickle in 26 of 29 cases. Patch testing performed in 11 of 29 patients was positive in all. The researchers presumed that the remaining patients have allergies by history alone. However, researchers are still unsure as to how many individuals with coronary artery disease might be affected.
Dr. Gulati said:
"We do not routinely test for nickle allergy, so we don't know how many people coming to the cath lab have this problem. Still, out findings would suggest that the mechanism of skin reaction to metal exposure might differ from that within the arterial wall."
At present, warnings about potential contraindications in individuals with metal allergies must be included in product labeling for stents marketed in the United States. According to Dr. Gulati, although there is not much data to support these warnings, caution is still recommended and further studies are required.