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WASHINGTON -- While monitoring for arrhythmias in high-risk patients following myocardial infarction (MI) commonly detected rhythm events requiring treatment within 2 years, treatment did not lead to better outcomes, according to the BIO|GUARD-MI study.

Among the patients who had a cardiac monitoring device implanted, 39% were found to have arrhythmias that required treatment compared with 6% of the control patients, but treatment did not translate to freedom from experiencing the primary endpoint of cardiovascular mortality or hospitalization for arrhythmias, acute coronary syndrome, worsening of heart failure, stroke, systemic embolism, or major bleeding (HR 0.84, 95% CI 0.64-1.10, P=0.21), reported Christian Jons, PhD, of Rigshospitalet Copenhagen in Denmark, during the American College of Cardiology (ACC) meeting.

"Part of the reason the BIO-GUARD study did not have a positive result may simply be that the background therapy has just gotten so good," said ACC President Edward Fry, MD, of Ascension's St. Vincent Medical Group in Indianapolis.

"As medical treatment gets better and better with universal treatment with beta-blockers, spirolactones, the early institution of sacubitril/valsartan, and now we have SGLT2 inhibitors, it becomes more difficult for another therapy to change the outcome to show benefit," he told MedPage Today, noting that other major non-medical obstacles to wider use of implanted cardiac monitoring include costs and reimbursement issues.

While there were mostly no significant differences between the prespecified subgroups, the patients who had a non-ST segment elevated myocardial infarction (NSTEMI) had fewer primary endpoint events with monitoring compared with no monitoring (HR 0.69, 95% CI 0.49-0.98). This was not the case for patients with STEMI (HR 1.10, 95% CI 0.72-1.69; P=0.09).

"In the predefined subgroup of NSTEMI patients, primary endpoints were reduced by 31%," Jons noted. "This benefit appears to be associated with a higher risk in NSTEMI patients."

Noting the difference in outcomes between patients with STEMI and those with NSTEMI, discussant Roxana Mehran, MD, of Mount Sinai Hospital in New York City, told Jons that she hoped he would validate this important endpoint. "Because your study was terminated early, the number of events for the primary endpoint did not reach what was needed and what you sampled for upfront."

The BIO-GUARD-MI study was designed to evaluate 372 primary endpoint events, but was beset by inconsistencies in reporting. These inconsistencies were observed at the first interim analysis, and the decision was made to truncate the trial in order to resolve the reporting issues and inherent bias in the reports. At that time, 218 patients had experienced a primary endpoint event.

The study included 790 patients who were considered to be high risk by their CHA₂DS₂-VASc score following MI, with a score of ≥4 for men and ≥5 for women making them eligible for the trial. Patients with a history of atrial fibrillation were excluded from the study.

Of the 398 participants randomized to monitoring with an implanted device, mean age was 72 years, 73% were men, 60% had a history of diabetes, and 17% had more than one MI. Of the 392 randomized to the control group, mean age was 71 years, 71% were men, 62% had a history of diabetes, and 18% had more than one MI.

Among the patients who required treatment, about 40% were treated with oral anticoagulants, about 20% were given pacemakers, and about 8% were given anti-arrhythmia drugs.

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