Implantable Monitors Help Improve Risk Prediction Following Myocardial Infarction

Professor Axel Bauer

Results of the SMART-MI suggest remote monitoring through implantable cardiac monitors (ICM) could help identify patients at increased risk for complications in high-risk post-infarction patients.

A prospective, randomized trial conducted in 400 patients, results of the study indicate use of ICMs was associated with a 6-fold increase in the detection of serious arrhythmias in a patient population with an ejection fraction that would normally preclude them from receiving such a device.

“The study found that post-infarction patients with cardiac autonomic dysfunction and only moderately reduced LVEF developed a high number of serious subclinical arrhythmic events that could be detected early and effectively with ICMs,” said principal investigator Axel Bauer, MD, professor of cardiology at the Medical University of Innsbruck, Austria, in a statement.

Presented at the European Society of Cardiology (ESC) Congress 2021, the SMART-MI study was a prospective, randomized, open-label trial conducted from May 2016-February 2021 at 33 sites in Germany and Austria. Designed with the intent of assessing whether ICMs could improve early detection of arrhythmias in patients with an ejection fraction greater than 35%, the study enrolled 400 patients and randomized them in a 1:1 ratio of ICM implantation and remote monitoring or conventional follow-up.

To be considered eligible for inclusion in the trial, patients were required to have a history of myocardial infarction with a left ventricular ejection fraction of 36-50% and cardiac autonomic dysfunction. Investigators noted autonomic dysfunction was identified using digital biomarkers calculated from a 20-minute high-resolution resting electrocardiogram. All patients who received ICM had the monitor implanted subcutaneously in a minimally invasive procedure and a telemonitoring system provided daily reports to an ICM core lab. Investigators pointed out study sites were notified about detection of serious arrhythmic events by this same ICM core lab.

The primary outcome of interest for the study was time to detection of serious arrhythmic events. For the purpose of analysis, serious arrhythmic events included atrial fibrillation lasting 6 minutes or longer, higher-degree atrioventricular block, fast non-sustained ventricular tachycardia (VT), and sustained VT/ventricular fibrillation. Secondary outcomes of interest included incidence of major adverse cardiac and cerebrovascular events (MACCE), which consisted of cardiovascular mortality, stroke, systemic arterial thromboembolism, and unplanned hospitalization for decompensated heart failure.

During the follow-up period, which lasted a median of 21 months, the primary outcome occurred among 29.9% (n=60) of patients in the ICM group and 6.0% (n=12) of patients in the control arm of the trial (HR, 6.3 [95% CI, 3.4-11.8]; P <.0001). Results suggested the cumulative 3-year detection rate of serious arrhythmic events was 41.2% among those in the ICM group and 10.7% among those in the control arm. Additionally, further analysis indicated the detection of serious arrhythmic events strongly predicted incidence of subsequent MACCE among those in the ICM group (HR, 6.8 [95% CI, 2.9-16.2]; P <.001) and control arm (HR, 7.3 [95%CI, 2.4-22.8]; P <.001) of the study.

“The important difference was the sensitivity in detection, which was three times higher in the ICM group (61% vs 20%; P=.007). This means that adverse outcomes were 3 times more likely to be detected early in the ICM group,” Bauer noted.

“The spectrum and frequency of arrhythmias in these patients was comparable to that of post-infarction patients with reduced LVEF, who are currently candidates for prophylactic ICD therapy. Our study supports the use of ICMs in high-risk post-MI patients with moderately reduced LVEF and cardiac autonomic dysfunction as a sensitive tool for continuous risk assessment,” Bauer continued.

This study, “Implantable cardiac monitors in high-risk post-infarction patients with cardiac autonomic dysfunction and moderately reduced left ventricular ejection fraction - A randomized trial,” was presented at ESC Congress 2021.