ICMs Detect Serious Arrhythmias in High-Risk Post-MI: SMART-MI

Theodore Bosworth

August 27, 2021

After a myocardial infarction, implantable cardiac monitors (ICMs) are sensitive for detecting serious arrhythmias in patients with cardiac autonomic dysfunction but only moderately reduced left ventricular ejection fraction (LVEF), according to results of the randomized SMART-MI trial.

When remote monitoring with the ICM was compared with conventional follow-up in this group of patients, serious arrhythmic events were detected at a nearly sixfold greater rate, reported Axel Bauer, MD, at the annual congress of the European Society of Cardiology.

The study further showed that these events were closely associated with subsequent major adverse cardiac and cerebrovascular events (MACCE).

"SMART-MI is the first study to test an implantable device in high-risk MI patients with a LVEF greater than 35%," reported Bauer, a cardiologist and director of the internal medicine clinic, University of Innsbruck (Austria). It showed that the types and frequency of arrhythmias were "comparable to those of post-MI patients with reduced LVEF."

The ability to assess risk is potentially significant because "the majority of cardiovascular complications, including sudden death, occur in patients with only moderately reduced LVEF," explained Bauer.

Despite the greater risk, "there are no preventive strategies so far" currently available for this group, he said.

The SMART-MI study confirms the need for treatments, confirms a method for monitoring risk, and might provide the basis for trials designed to test treatments to modify this risk, he added.

ECG Used to Define Autonomic Dysfunction

In the SMART MI protocol, 1,305 survivors of MI with LVEF of 36%-50% at 33 participating centers in Austria and Germany were evaluated with a 20-minute high resolution electrocardiogram. They were enrolled and randomized if they demonstrated cardiac autonomic dysfunction on at least two validated ECG biomarkers.

The 400 participants were randomized to implantation of a ICM, which transmitted daily reports to a ICM core laboratory, or to conventional follow-up.

After a median follow-up of 21 months, serious events were detected in 60 of the 201 patients in the ICM group and 12 of the 199 patients in the control group (29% vs. 6%). Serious adverse events were defined as those that would typically warrant therapy, such as prolonged atrial fibrillation (at least 6 minutes) high-degree atrioventricular block, and sustained ventricular tachycardia.

The difference in the detection rate, which was the primary endpoint, was highly significant (< .0001), but the study was also able to confirm that these events predicted MACCE, a secondary study endpoint. In those with a serious arrhythmia, the hazard ratio for subsequent MACCE was approximately sevenfold greater relative to those without a serious arrhythmia. This was true of those in the ICM group (HR, 6.8; < .001) and controls (HR 7.3; P < .001).

Arrhythmias Warn of Impending Complications

"The data show that the prognostic impact of detecting a serious arrhythmia does not depend on the mode of detection," Bauer reported. The data also confirm that "subclinical serious arrhythmia events are a warning signal for an impending complication."

Although more interventions – including pacemakers, catheter ablations, and oral anticoagulants – were offered to patients in the experimental arm, "the study was not powered to show differences in outcomes," and, in fact, no significant differences were observed, according to Bauer. However, the evidence that ICM is effective for detecting arrhythmias does provide a structure on which to build clinical trials.

"We now need the trials to see if ICM can change practice and improve outcomes," said Carlos Aguiar, MD, a staff cardiologist at the Hospital Santa Cruz, Lisbon. He acknowledged that this study proves that ICM can detect serious arrhythmias in patients with moderate left ventricular dysfunction, but "we need to develop and test treatment paths."

Aguiar considers SMART-MI an important study that "goes to the heart" of a common clinical dilemma.

"In clinical practice, we see patients with LVEF that is not that suppressed and so do not have a class I indication for ICM, but there are often features that might have you concerned and make you think it would be great if the LVEF was 35% or lower [to justify intervention]," Aguiar said.

Data Provide Insight on Unaddressed Risk Group

SMART-MI confirms earlier evidence that post-MI patients with cardiac autonomic dysfunction are at high risk. Currently, this relative increase in risk goes "unaddressed," according to Bauer. Although he contended that the risk itself "could be an indication for ICM in a high-risk patient group without classically defined left ventricular dysfunction," he agreed that the ultimate value of this trial might be that it "opens a window" for a rationale to test preventive strategies.

An invited ESC discussant, Gerhard Hindricks, MD, PhD, praised the study for drawing attention to the risk of events in a subset of post-MI patients with LVEF of 35% or greater. However, he suggested that criteria other than those based on ECG might be more sensitive for selecting patients who might benefit from intervention.

"We do not know whether additional methods of establishing risk, such as imaging, might be valuable," said Hindricks, chief of the department of arrhythmology in the Heart Institute of the University of Leipzig (Germany). He believes work in this area is needed to ensure appropriate entry criteria for interventional trials designed to modify risk in post-MI patients who do not meet the traditional definition of reduced ejection fraction.

Bauer reports financial relationships with Medtronic, which sponsored this study, as well as Bayer, Boehringer Ingelheim, Edwards, and Novartis. Aguiar reports no relevant financial conflicts.

This article originally appeared on MDedge.com, part of the Medscape Professional Network.

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