Implantable Cardiac Monitors in High-Risk Post-Infarction Patients With Cardiac Autonomic Dysfunction

Sudden cardiac death (SCD) is the most common single cause of death in the industrialized world. Patients after myocardial infarction (MI) are at increased risk of SCD. Current guidelines recommend prophylactic ICD-implantation in post-MI patients with reduced left ventricular ejection fraction (LVEF ≤35%). However, the majority of arrhythmic deaths after MI occurs in patients with LVEF >35% in whom no specific prophylactic strategies exist, indicating an important unmet medical need.

There is a large body of evidence that presence of cardiac autonomic dysfunction after MI is associated with an increased susceptibility to malignant brady- and tachyarrhythmias eventually culminating in SCD. Periodic repolarization dynamics (PRD) and heart rate deceleration capacity (DC) are clinically validated autonomic risk markers that provide strong and independent prognostic information in post-MI patients with LVEF >35%. PRD and DC reflect different facets of autonomic function and can therefore be used in combination to predict risk. Previous studies demonstrated that combined assessment of PRD and DC identifies a new high-risk group among post-MI patients with moderately reduced LVEF (36-50%). This new high-risk group has similar characteristics with respect to prognosis and patient numbers as the established high-risk group identified by LVEF ≤35%.

However, the exact mechanisms leading to death in this new high-risk group need to be investigated in order to develop specific preventive strategies. As known from studies with implantable cardiac monitors (ICM) in post-MI patients with LVEF ≤40% eventual death is often preceded by primarily asymptomatic serious arrhythmic events. These data suggest a potential time frame for pre-emptive interventions in case of arrhythmic events, which could improve outcome.

Therefore, SMART-MI will assess the occurrence and prognostic implications of serious arrhythmic events in this newly identified high-risk group by remote monitoring with ICM. Survivors of acute MI (<40 days) and LVEF 36-50% undergo autonomic testing for presence of abnormal PRD and/or DC. Those with autonomic dysfunction will be randomly assigned to ICM-implantation or conventional follow-up. Superiority of ICMs in detection of predefined serious arrhythmic events will be tested based on a time-to-event analysis. A central ICM core lab will be implemented allowing for a response to arrhythmias within 48h. The effect of remote monitoring on clinical outcomes will be tested as secondary endpoints. The study will provide the rationale for a future guideline-relevant study testing prophylactic therapies in this newly identified high-risk group.

Inclusion criteria

• Acute myocardial infarction <40 days
• Left ventricular ejection fraction 36-50%
• Presence of cardiac autonomic dysfunction by means of abnormal periodic repolarization dynamics and/or abnormal deceleration capacity
• Age 18-80 years
• Sinus rhythm
• Optimal medical therapy

Exclusion criteria

• ICD or pacemaker indication
• Known paroxysmal or persistent atrial fibrillation
• Life expectancy < 12 months
• Inability to comply with follow-up
• Pregnancy
• Participation in another trial that may interfere