CardioExchange Archive

With a result that is likely to surprise and baffle much of the mainstream medical community, a large NIH-sponsored trial has turned up the first substantial evidence in support of chelation therapy for patients with coronary disease. Known as TACT (Trial to Assess Chelation Therapy), the highly controversial trial was presented today at the American Heart Association conference by Gervasio Lamas. The trial was sponsored by two NIH institutes, the National Center for Complementary and Alternative Medicine and the National Heart, Lung, and Blood Institute.

Chelation therapy with disodium ethylene diamine tetra acetic acid (EDTA) to remove heavy metals from the blood to treat coronary disease has been around — and provoked criticism — since the 1950s. Despite a lack of evidence and the skepticism of the medical community, passionate supporters have kept the therapy alive in alternative medicine circles.

TACT was funded by the NIH more than a decade ago as part of a much-publicized initiative to study the claims of alternative medicine. In 2008, enrollment in TACT was temporarily suspended in response to claims that the trial was unethical. The trial was additionally hampered by slow enrollment.

Now, the results of TACT will likely provide ammunition to chelation defenders, but the trial investigators and other experts have expressed considerable caution about the proper interpretation of the results.

TACT was a double-blind study testing active or placebo infusions of chelation in stable patients with a history of MI. Due to slow enrollment, the trial was downsized, ultimately enrolling 1,708 patients instead of the planned 2,372. To maintain the trial’s power to achieve a meaningful result, the follow-up time was increased. Because of this change, and because the data and safety monitoring board reviewed the data multiple times over the course of the study, the threshold for statistical significance was lowered to 0.036.

The primary endpoint of the trial — the composite of death, MI, stroke, coronary revascularization, or hospitalization for angina — was significantly lower in the chelation group:

• 26.5% in the chelation group versus 30% in the placebo group (HR 0.82, 0.69-0.99, p=0.035)

There were no significant differences in any of the individual components of the primary endpoint. Most of the difference between the groups was due to a lower rate of coronary revascularization in the chelation group:

• 15.5% versus 18.1% (HR 0.81, CI 0.64-1.02, p=0.076)

Nearly all of the benefit in the trial was found to occur among the one-third of patients who had diabetes:

• 67 events in the chelation group versus 102 events in the placebo group (HR 0.61, CI 0.45-0.83, p=0.002)

The investigators were cautious in their interpretation, noting that the trial barely achieved statistical significance, most of the difference was found in the softer endpoint of revascularization, and the finding is less reliable since there was a high withdrawal rate (17%) of patients in the trial.

The authors said that their findings were “unexpected and additional research will be needed to confirm or refute our results and explore possible mechanisms of therapy.” TACT, they concluded, “does not constitute evidence to recommend the clinical application of chelation therapy.”

At an AHA press conference, Paul Armstrong said that TACT was a response to an unusual situation. On the one hand, most physicians and scientists have dismissed chelation therapy as lacking any evidence or rationale. On the other hand, chelation therapy is strongly supported by the alternative medicine community and more than 100,000 people receive chelation therapy each year. Armstrong said the results of the trial were “hypothesis generating, not practice changing.”