Patients who survive an acute myocardial infarction (MI) with diminished left ventricular (LV) function experience frequent and treatable arrhythmias, according to findings from the Cardiac Arrhythmias and Risk Stratification after Myocardial Infarction (CARISMA) observational study. Moreover, high-degree atrioventricular (AV) block appears to independently predict cardiac death in the post-MI patient population.

“The insertable ECG loop recorder is a diagnostic tool that should be considered to guide medical and device therapy in patients who survive myocardial infarction,” said Poul Erik Bloch Thomsen, MD, Gentofte University Hospital, Copenhagen, Denmark, principal investigator of the CARISMA trial.

CARISMA is the first long-term observational study to examine implantable loop recorder data among post-MI patients. The study was designed to determine the risk of tachyarrhythmia and sudden death in patients who do not meet the criteria for an implantable cardioverter defibrillator (ICD) despite mild to moderate structural damage following an acute MI.

In CARISMA, investigators implanted insertable loop recorders in 297 patients an average of 11 days after MI. All patients had a low ejection fraction (EF<40%), and none had an ICD. During a 2-year follow-up, the loop recorders provided information every 4 months on the incidence of any arrhythmias: sinus bradycardia, sinus arrest, atrial fibrillation (AF), second or third degree AV block, ventricular tachycardia (VT), and fibrillation.

After a mean follow-up of 1.9 years, 137 patients (46%) had evidence of at least one of the pre-specified arrhythmias, of which only 14% was symptomatic.

New AF (≥125 bpm), the most frequent arrhythmia, was documented in 27% of patients. Sinus bradycardia (<30 bpm), AV block (<30 bpm), non-sustained VT (≥125 bpm, ≥16 beats), and sustained VT (≥125 bpm, ≥30 seconds) were each observed in approximately 17% of patients.

In a univariate analysis, AV block (HR 7.0; p=0.0004), sinus bradycardia (HR 5.8; p=0.004), and non-sustained VT (HR 3.4; p=0.025) appeared to predict cardiac death. However, by multivariate analysis, high-degree AV block remained the only independent predictor of cardiac death (HR 4.8; p<0.001).

Despite the highly significant correlation between AV block and death, differentiating between all-cause cardiac death and sudden cardiac death secondary to ventricular arrhythmias is difficult, Dr. Thomsen said. To investigate this issue, CARISMA investigators are performing additional analyses to further explore the relationship between baseline left bundle branch block and subsequent risk of fatal ventricular arrhythmias and AV block.

In summary, findings from the CARISMA observational study suggest that an implantable ECG loop recorder—typically used to identify the cause of syncope—may help clinicians risk-stratify patients with reduced LV function following acute MI.