Heart rhythm monitor implanted after MI does not prevent CV events
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WASHINGTON — In patients with MI at high risk for stroke, implanting a loop recorder did not impact subsequent CV events, according to the results of the BIO | GUARD-MI trial.
However, among patients with non-STEMI, those who received the implantable loop recorder (BioMonitor 2, Biotronik) had reduced risk for CV events compared with those who did not, Christian Jøns, MD, PhD, an electrophysiologist at Rigshospitalet in Copenhagen, said during a presentation at the American College of Cardiology Scientific Session.
While it is known that patients with MI are at elevated risk for arrhythmias, which are associated with poor outcomes, “there has been no trial designed to investigate whether responding to or treating these arrhythmias would improve outcomes in post-infarction patients,” he said during the presentation. “The BIO | GUARD-MI trial was designed to do just that.”
The researchers randomly assigned 398 patients (mean age, 72 years; 73% men) to the implantable loop recorder and 392 patients (mean age, 71 years; 71% men) to standard care. All patients had a recent MI and a CHA2DS2-VASc score of at least 4 for men and at least 5 for women.
The primary endpoint was CV death or hospitalization for any of the following: arrhythmia, ACS, worsening of HF, stroke, systemic embolism or major bleeding.
At 2 years, 67% of the monitoring group had any arrhythmia, and 39% of the group was being treated for an arrhythmia. By contrast, only 6% of the control group was being treated for an arrhythmia at 2 years (HR = 5.9; P < .0001), Jøns said during the presentation.
In the overall cohort, there was no difference between the groups in the primary outcome (HR = 0.84; 95% CI, 0.64-1.1; P = .21), according to the researchers.
However, Jøns said, the primary outcome favored the monitoring group in patients with non-STEMI (HR = 0.69; 95% CI, 0.49-0.98) but not in patients with STEMI (HR = 1.1; 95% CI, 0.72-1.69), with interaction barely missing significance (P for interaction = .09).
Patients with non-STEMI had greater risk for the primary outcome than patients with STEMI (HR = 1.75; 95% CI, 1.33-2.3; P = .0003), he said.
“Arrhythmia monitoring in high-risk post-infarction patients identified arrhythmias requiring treatment in nearly 40% of the patients within 2 years,” Jøns said during the presentation. “In the total study population, this did not cause a difference in the incidence of the primary outcome. However, in the predefined subgroup of non-STEMI patients, we did see a 30% reduction in the outcome. This benefit appeared to be the result of higher risk in the non-STEMI group.”
“The thing that intrigues me most is ... where you showed very sharp and very early takeoff in the curve for detection of arrhythmias and for arrhythmias requiring treatment between the group that received an implantable monitor vs. control,” Julia H. Indik, MD, PhD, professor of medicine and Flinn Foundation and American Heart Association Endowed Chair in Electrophysiology and Heart Disease Research at the University of Arizona College of Medicine in Tucson, said during a discussion after the presentation. “The most common treatment employed was anticoagulation. Was there a relationship between anticoagulation and the primary endpoint or components of it?”
Jøns said the most common events in the non-STEMI population were ACS and worsening HF, and those events were much lower in the STEMI population. He said there were few strokes, and there was no difference between the STEMI and non-STEMI cohorts in all-cause or CV mortality.
Perspective
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Chirag R. Barbhaiya, MD, FHRS
Incidence of significant arrhythmias increases along with increased comorbidity, and MI is a significant comorbidity. MI increases the risk for a number of clinically important arrhythmias.
The study's finding that patients with greater comorbidities were at greater risk of significant arrhythmia makes a lot of sense. I look forward to seeing the full results of the trial to better understand exactly what arrhythmias were observed, and what were the key drivers of the primary endpoint. It seems that most of the events were related to detection of atrial fibrillation, and detection of arrhythmias that prompted pacemaker implantation. I would really like to see whether the events that drove the primary endpoint were hard clinical endpoints, or if they were hospitalization for asymptomatic bradycardia or AF that could likely have been managed without hospitalization.
Counterintuitively, the non-STEMI population appears to have been a more heterogenous population with more comorbidities. Thus, despite having a lower severity of MI, the non-STEMI population was a sicker population at greater risk for incident arrhythmia.
Arrhythmia monitoring using implantable and wearable devices is going to be an exciting and important area of research going forward. As the technology continues to improve to make it smaller, cheaper, and more accurate, the level of risk needed to justify monitoring will continue to decrease.
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Jøns C, et al. Late-Breaking Clinical Trials V. Presented at: American College of Cardiology Scientific Session; April 2-4, 2022; Washington, D.C. (hybrid meeting).
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