Reviwer : Dr. Dursun Akaslan

Name of the Study: Implantable cardiac monitors in high-risk post-infarction patients with cardiac autonomic dysfunction and moderately reduced left ventricular ejection fraction: SMART-MI DZHK9

Published Congress: ESC 2021

Link: https://www.sciencedirect.com/science/article/abs/pii/S0002870317301473?via%3Dihub

Background:

Intracardiac defibrillator (ICD) therapy is recommended for prevention of sudden cardiac death in patients with severely reduced left ventricular ejection fraction (LVEF; 35% or less) after myocardial infarction (MI). Most cardiovascular complications after MI occur in patients with a left ventricular ejection fraction >35%. MI can cause severe damage to the autonomic nervous system at various levels of cardiac neuroaxis. Cardiac autonomic dysfunction after MI is associated with poor prognosis, independent of LVEF. Cardiovascular complications can occur with subclinical arrhythmic events. However, since most of these arrhythmias are asymptomatic or subclinical, their detection overlooked conventional follow-up. Remote monitoring of implantable cardiac monitors (ICMs) is highly effective for early detection of severe arrhythmias in high-risk post-infarction patients with cardiac autonomic dysfunction. The SMART-MI study examined whether ICMs could provide early detection of such arrhythmias.

Objective:

The aim of this study is to evaluate whether ICMs are superior to traditional follow-up in detecting severe arrhythmic events in patients with moderate heart failure (LVEF 35-50%), high-risk MI, and cardiac autonomic dysfunction.

Methods:

33 centers from Germany and Austria were included in the SMART-MI study between May 2016 and February 2021. Patients with LVEF 35-50% and sinus rhythm in acute MI patients who underwent primary PCI and did not exceed 40 days were included in the study. For the diagnosis of autonomic dysfunction, 20-minute high-resolution ECG recordings were examined and the presence of Deceleration capacity (DC) and Periodic repolarization dynamics (PRD) findings were investigated. Autonomic dysfunction was detected in 400 of 905 patients included in the study. These patients were randomized 1:1 to intracardiac monitoring (ICM) and conventional follow-up. ICMs were placed under the skin with minimal surgical intervention. The patients were followed up for an average of 21 months. The primary endpoint was defined as serious arrhythmic event (SArE) detection. Criteria for SarE was defined as an attack of atrial fibrillation longer than 6 minutes ,severe AV block (>2b) and detection of nonsustained VT longer than 40 beats or sustained VT/VF. The secondary endpoint was also defined as death and MACCE.

Results:

In this study, while serious arrhythmic event was detected in 60 patients in the ICM group (43 AF, 10 AV block, 7 VT/VF), it was detected in only 12 patients (11 AF, 1 VT/VF) in the control group( HR; 95% 6.3 (3.4-11.8) ), p<0.0001). In the analysis performed by excluding AF events, 23 events were observed in the ICM group, while 2 events were detected in the control group (HR; 95% 12.2(2.9-51.7), p<0.0001). As a secondary outcome, no significant difference was found in mortality rates (HR; 95% 1.3(0.5-3.1), p:0.580) and MACCE (HR;95% 1.0(0.6-1.8), p: 0.910) . However, the detection of SArE was found to predict MACCE. (HR; 95%, 6.82(2.86-16.22), p<0.001).

Conclusion:

In post MI patients with autonomic dysfunction and LVEF 35-50%, a high number of subclinical brady and tachyarrhythmias could be detected effectively by monitoring with ICM. SArEs detected by the ICM are considered to be high predictors for cardiovascular complications. Early recognition of subclinical SAREs will open a new window for preventive interventional treatment opportunities.

Interpretations:

SMART-MI is a diagnostic study and is not sufficient to detect clinical outcomes with its low study sample and short follow-up time. The findings in the ASSERT study that subclinical atrial tachycardias increase the risk of stroke could not be fully demonstrated in this study. I think that the use of different diagnostic tools is effective in the absence of difference in terms of death and MACCE. It is also important that SARes are found to be predictive of MACCE .  In conclusion, this study for the early diagnosis of subclinical arrhythmias revealed that prospective preventive interventional treatments should be considered in patients with moderate heart failure.