Treating Cardiac Arrhythmias Detected With an Implantable Cardiac Monitor in Patients After an Acute Myocardial Infarction

Abstract

Using an implantable cardiac monitor (ICM) in patients with acute myocardial infarction (MI) allows continuous electrocardiogram monitoring and provides a much more detailed picture of the incidence of brady- and tachyarrhythmias than conventional follow-up. The CARISMA study was the first to use the ICM in post-MI patients with moderate to severe left ventricular systolic dysfunction. Atrial fibrillation (AF) events lasting longer than 30s were associated with an almost threefold increase in the risk of major cardiac events. This confirms the current definition of clinically significant AF episodes, as patients with episodes of shorter duration were not at increased risk. The association of AF to progressive heart failure, reinfarction, and cardiovascular death underlines the need for an intensive follow-up of post-MI patients with new-onset AF in order to reveal underlying causes of AF such as progressive left ventricular dysfunction or myocardial ischemia. Asymptomatic, especially nightly, bradycardia episodes including high-degree 2°-3° atrioventricular (AV) block, sinus bradycardia, and sinus arrest were frequently documented by ICM in the CARISMA study. Ten percent of patients experienced high-degree 2°-3° AV block, of which the main part was nightly and asymptomatic, and 50% of all cardiovascular deaths occurred in this group, most from severe heart failure. Therefore, in post-MI patients with paroxysmal high-degree AV block, pacemaker implantation should be done, and in the case of left ventricular dysfunction (LVEF ≤ 35%), an implantable cardioverter defibrillator/cardiac resynchronization therapy defibrillator (ICD/CRT-D) may be indicated. Nonsustained ventricular tachycardia (VT) is very frequent in post-MI patients, and in the CARISMA study, high-risk patients with nonsustained VT were implanted with an ICD. Furthermore, in 10% of the patients, the ICM recorded nonsustained VT episodes of ≥ 16 beats per minute, resulting in a twofold increase in the risk for cardiac death. Thus, patients with nonsustained VT should undergo careful investigation, and we recommend a repeat echocardiography and electrophysiological stimulation in these patients. Patients with sustained VT or VF should receive an ICD.