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Hot Line - Do implantable cardiac monitors improve post-MI arrhythmic event detection?

27 Aug 2021
Hot Line presented at ESC Congress

Yes, according to a Hot Line presentation by Professor Axel Bauer (Innsbruck Medical University, Austria). Prophylactic implantable cardioverter defibrillators (ICDs) are available for patients with severely reduced left ventricular ejection fraction (LVEF, <=35%) after myocardial infarction (MI). However, no standard prophylactic measures are used for patients with LVEF >35%, despite the fact that most post-MI complications occur in this group.

The prospective, 1:1 randomised, open-label SMART-MI trial investigated the use of implantable cardiac monitors (ICMs) compared with conventional follow-up in 400 high-risk, post-infarction patients with LVEF 36–50% and cardiac autonomic dysfunction (abnormal periodic repolarisation dynamics [>=5.75 deg2] and/or abnormal deceleration capacity [<=2.5 ms]). ICMs were implanted subcutaneously and daily reports were transmitted via a telemonitoring system. The primary endpoint was time to detection of serious arrhythmic events, which included atrial fibrillation lasting six minutes or more, higher-degree atrioventricular block, fast non-sustained ventricular tachycardia (VT) and sustained VT/ventricular fibrillation.

During a median follow-up of 21 months, serious arrhythmic events occurred in 60 (29.9%) patients in the ICM arm and 12 (6.0%) patients in the control arm (hazard ratio [HR] 6.3; 95% confidence interval [CI] 3.4 to 11.8; p<0.0001). The improved detection rate with ICM was apparent for all types of serious arrhythmic events. The cumulative 3-year detection rate of serious arrhythmic events was 41.2% in the ICM arm and 10.7% in the control arm. ICM had a higher detection sensitivity than conventional follow-up (61% vs. 20%; p=0.007), such that adverse outcomes were three-times more likely to be detected early in the ICM group.

Serious arrhythmic events strongly predicted the occurrence of subsequent major adverse cardiac and cerebrovascular events in both the ICM (HR 6.8; CI 2.9 to 16.2; p<0.001) and conventional follow-up (HR 7.3; 95% CI 2.4 to 22.8; p<0.001) arms. There was no difference in the positive predictive accuracy between the detection modalities (61% with ICM and 62% with conventional follow-up).

Prof. Bauer observed, “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. 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.”


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