Implantable cardiac monitoring (ICM) of high-risk patients who had suffered a myocardial infarction (MI) did not reduce future cardiovascular events overall, but benefit was seen in NSTEMI patients compared with STEMI patients, according to the results of the BIO|GUARD-MI study presented April 4 at ACC.22.

The trial was stopped earlier than anticipated because of an unexpectedly high rate of noncardiovascular events detected among patients who received an ICM device at the time of the first interim analysis. Enrollment was paused while researchers and the sponsor worked to reduce this bias. The issue was eventually resolved.

Researchers enrolled 802 patients with a previous MI (about one-half NSTEM and one-half STEMI) at 60 medical centers in 14 countries in Europe, Australia and the U.S. Before hospital discharge, half of the patients were randomly assigned to receive an implantable loop recorder. The researchers tracked arrhythmias and outcomes for a median of about 2.5 years. The average age of the patients was 72 years, most were men (about 73%). The average CHA2DS2-VASc score was about 4.8.

A total of 218 patients experienced a primary endpoint event, defined as a composite of cardiovascular death or acute unscheduled hospitalization for heart failure, arrhythmia, acute coronary syndrome, stroke, major bleeding or systemic embolism. While a trend was revealed toward reduced primary endpoints in patients with an ICM, the difference was not statistically significant (hazard ratio, 0.84; p=0.21).

The researchers found that patients with an NSTEMI had a 75% increased risk of suffering a primary endpoint event. Furthermore, the prespecified sub-analysis found that NSTEMI patients who received an ICM were about 30% less likely to experience the primary composite endpoint.

The researchers also noted that a greater proportion of patients who received ICM had their therapy adjusted to account for arrhythmias. This suggests the monitors were useful in alerting doctors to heart rhythm problems such as atrial fibrillation.

Differences in the health status of patients who experience NSTEMI and STEMI heart attacks, along with differences in the treatments they receive, could account for the differences observed in the study, noted the researchers.

"In NSTEMI patients, we found that diagnosing an investigated asymptomatic arrhythmia with an implantable cardiac monitor prevented cardiac events, whereas it didn't in STEMI patients," said Christian Jøns, MD, an electrophysiologist at Rigshospitalet in Copenhagen, Denmark and the study's lead author. "Even though the main study was negative, our sub-analysis indicates that NSTEMI patients could benefit from continuous [heart rhythm] monitoring and intervention."

Clinical Topics: Stable Ischemic Heart Disease, Vascular Medicine, Chronic Angina

Keywords: ACC Annual Scientific Session, ACC22, ST Elevation Myocardial Infarction, Myocardial Infarction

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