Implantable cardiac monitor improves arrhythmia detection in high-risk patients post-MI
In high-risk patients with a prior MI and cardiac autonomic dysfunction, use of an implantable cardiac monitor increased the detection rate of serious arrhythmic events compared with conventional follow-up.
Results of the SMART-MI trial, presented at the European Society of Cardiology Congress, showed that subsequent major adverse CV events were highly likely following the detection of an arrhythmic event, regardless of the method of detection. However, the use of an implantable cardiac monitor demonstrated greater sensitivity compared with usual care.
“In SMART-MI, we targeted a previously unaddressed high-risk population of post-infarction patients with ejection fraction above 35% and showed that telemedical monitoring with implantable cardiac monitors is highly effective in early detection of serious, prognostically relevant, arrhythmic events,” Axel Bauer, MD, professor of cardiology at the Medical University of Innsbruck, Austria, said during a press conference. “The majority of cardiovascular complications, including sudden death after myocardial infarction occur in patients with ejection fraction above 35%. For these patients, no preventive strategies exist. Previous studies have clearly demonstrated that cardiac autonomic dysfunction after myocardial infarction can identify high-risk patients, irrespective of ejection fraction. SMART-MI is the first study to test the use of implantable devices, in general, in high-risk post-MI patients with ejection fraction above 35%.”
The prospective, randomized, open-label trial enrolled 400 patients with a prior MI, left ventricular EF between 36% and 50%, and cardiac autonomic dysfunction. Patients were randomly assigned to receive a subcutaneous implantable cardiac monitor and remote monitoring (Reveal LINQ, Medtronic) or conventional follow-up.
The primary endpoint was detection of a serious arrhythmic event, including AF lasting at least 6 minutes, higher-degree atrioventricular block, nonsustained ventricular tachycardia and sustained ventricular tachycardia/ventricular fibrillation.
Over a median follow-up of 21 months, the primary endpoint occurred in 29.9% of patients who received an implantable cardiac monitor compared with 6% of patients who received conventional follow-up, indicating that implantable cardiac monitoring was associated with a more than sixfold greater rate of detecting a serious arrhythmic event (HR = 6.3; 95% CI, 3.4-11.8; P < .0001). The cumulative 3-year detection rate of serious arrhythmic events was 41.2% in the implantable cardiac monitor group vs. 10.7% in the conventional follow-up group.
Moreover, detection of serious arrhythmic events strongly predicted subsequent major adverse CV and cerebrovascular events, including CV mortality, stroke, systemic arterial thromboembolism and unplanned hospitalization for decompensated HF, in both the implantable cardiac monitoring group (HR = 6.8; 95% CI 2.9-16.2; P <.001) and the conventional follow-up group (HR = 7.3; 95% CI, 2.4-22.8; P < .001).
Positive predictive accuracy was 60% in both groups.
“The prognostic impact of an arrhythmia does not depend on the mode of detection; however, the sensitivity of implantable cardiac monitor telemonitoring is tripled,” Bauer said.
The sensitivity to detect a serious arrhythmic event was higher with implantable cardiac monitoring, at 61% compared with 20% with conventional follow-up (P = .007).
In other results, an increased number of diagnostic and therapeutic measures were observed in the implantable cardiac monitoring group, including implantation of implantable cardioverter defibrillators or pacemakers, electrophysiological studies, catheter ablations and oral anticoagulation.
“Telemedical monitoring with implantable cardiac monitors allows for continuous cardiac risk assessment. This could be a new indication for implantable cardiac monitors, in general, in post-MI patients who do not meet the class criteria for reduced ejection fraction,” Bauer said during the press conference. “Subclinical serious arrhythmic events serve as warning signals for impending complications. This might open a window of opportunity for preventive interventions.
“However, our study was a diagnostic study, not powered to detect clinical differences. Therefore, future studies are needed to test whether continuous telemedical risk assessment by implantable cardiac monitors or other mobile devices indeed leads to improved clinical outcome.”
Perspective
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SMART-MI is a good direction finder in this group of patients who do not qualify for an indicated ICD after their acute MI. A significant proportion are still at risk for sudden death and other major events after MI, and so this helps us to start to sort out the next-highest-risk group, identifying who is at risk and then, hopefully, treating them successfully.
In general, these implantable cardiac monitors are low-risk devices and have relatively low costs compared with putting in an ICD or pacemaker. They can be put in as an outpatient relatively easily in just a few minutes and it's a great way to monitor these patients in a way that we haven't been able to do before.
However, SMART-MI wasn't large enough to inform or change clinical practice or guidelines. What it did show us was that these implantable devices are good and sensitive for detecting significant arrhythmic events. That's important because we haven't had any great long-term ways of doing this for our patients after acute MI. The higher-risk patients wore cumbersome vests, and many times would have to wear them for months, which can be quite awkward. For the lower-risk patients, having external monitors hooked up to them for 30 days or more can also be quite cumbersome. These implantable cardiac monitors are relatively simple devices that we're putting in subcutaneously and can be used for not just 30 days, but months on end, even up to 3 years. These devices are not only less cumbersome but are also efficient in detecting arrhythmic events.
What we haven't determined from this study, because it was too small, is whether or not detecting those arrhythmic events and subsequently acting on them actually changed outcomes in terms of major adverse CV events; specifically, reduced mortality. That would require a follow-up study of a larger scale.
This is the first study in this area with this device in this particular use. It is interesting and exciting because it gives us a new, relatively simple, tool to follow these patients, which we never had before. The next chapter is to find out if using this in a large number of patients for detecting these arrhythmias is actually as effective as it seems in this smaller study. Then we need to determine whether acting on those detected arrhythmic events does make a difference in the long run, particularly in terms of saving lives.
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Bauer A, et al. Hot Line: SMART-MI. Presented at: European Society of Cardiology Congress; Aug. 27-30, 2021 (virtual meeting).