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Hypersensitivity to metals does not appear to affect short- and long-term outcomes after coronary stent implantation, according to an analysis published online March 27, 2012, ahead of print in Circulation: Cardiovascular Interventions. But experts interviewed by TCTMD argue that the single-center, retrospective study has too many limitations to be definitive.

Rajiv Gulati, MD, PhD, and colleagues at the Mayo Clinic (Rochester, MN), identified 29 patients with known metal allergy who underwent coronary stent implantation. The investigators propensity-matched them with 250 nonallergic patients who also underwent stenting at the hospital.

Allergic and nonallergic patients were similar with respect to the number of segments treated (1.4 ± 0.7 vs. 1.5 ± 0.7), the number of stents placed (1.7 ± 1.1 vs. 1.6 ± 0.9), and frequency of DES use (52% vs. 60%).

In the allergic group, 26 patients were hypersensitive to nickel and 9 to chromium. Patch testing was performed in 11 of the patients and was positive in all cases. Yet there were no differences between the groups with regard to rates of in-hospital or 30-day mortality and MI (table 1).

Table 1. Short-term Outcomes

At 4 years, rates of mortality, TLR, and the composite of death, MI, and TLR were also similar between allergic and nonallergic patients (table 2).

Table 2. Four-Year Outcomes

 
Because DES might mask an allergically mediated effect on restenosis, a subgroup of allergic patients who received BMS was compared with matched controls. Even in this subset, however, no differences were seen between allergic and nonallergic patients in long-term death (P = 0.32), TLR (P = 0.46), or death, MI, or TLR (P = 0.34).

“I would venture that most interventional cardiologists have, at some stage, had the dilemma of whether to place a coronary stent in a patient with a history of skin allergy to one of the metal components (typically nickel),” said Dr. Gulati in an e-mail correspondence with TCTMD, noting that stent package inserts recommend avoiding use in such patients. “All that said, there have been only limited data from prior studies in patients with metal allergy [that] focused on the risk of restenosis. These studies had some limitations in design and yielded conflicting results.”

In a telephone interview with TCTMD, David E. Kandzari, MD, of the Piedmont Heart Institute (Atlanta, GA), said that although encountering someone with a nickel, chromium, or cobalt allergy is rare, “when it does occur, it makes everyone scratch their heads [about] what to do.”

Many Unanswered Questions

The presence of an allergy raises a host of unanswered questions, Dr. Kandazari said. “Is this just a topical reaction that could not be elicited with intravascular stent placement? Is the [metal content] so small that [the stent] does not evoke an inflammatory reaction when placed in the coronary artery? Or is the immunologic response in the vessel different from what it is topically?”

But allergist John R. Cohn, MD, of Thomas Jefferson University Hospital (Philadelphia, PA), was not surprised by the findings.

He told TCTMD in a telephone interview that the study has many limitations. Metal allergy was not objectively defined in most patients, and the composition of the stents was also not clearly defined. Moreover, with only 29 allergic patients out of nearly 14,000 treated during the study period, the investigators missed the vast majority of the metal allergic population if—as reported in the paper—the prevalence of metal allergy is 8%.

It is important to recognize that several factors influence allergic reactions, such as how the metal in a stent is processed, Dr. Cohn observed. “A great model for that is latex allergy,” he said. “We know that latex allergy is a problem. That doesn’t mean you’re going to have trouble with the tires on your car or the soles of your shoes, but you might have trouble with rubber gloves. They all contain natural rubber latex, but they’re all processed very differently, they’re bound very differently, and they present as an antigen very differently.”

Stent strut endothelialization over time may reduce the potential for allergies, Dr. Cohn said. Moreover, he pointed out, “some forms of exposure actually induce tolerance. Think of allergy shots.”

Reassuring but No Clear Answer for Practice

In a telephone interview with TCTMD, Ajay J. Kirtane, MD, SM, of Columbia University Medical Center (New York, NY), called the study “very reassuring,” especially since most interventionalists do not ask about a history of metal allergy prior to stent implantation.

When treating a patient with documented metal allergy, Dr. Kirtane said, “I would first try to find out [exactly which] metal the patient is allergic to. Then, I would probably still consult with an allergist and try to find a stent with no cross-reacting allergen.”

That might not be easy, noted Dr. Kandzari, because most stents contain nickel or chromium alloys. But the alternatives—angioplasty alone or surgery—for metal allergic patients who would otherwise be good candidates for stent placement are “a real challenge as well,” he added.

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