Results from the CARISMA (Cardiac Arrhythmias and Risk Stratification after Myocardial Infarction) trial have shown that a subcutaneous implantable monitor documented significant arrhythmias, more than three-quarters of which were asymptomatic, according to a study published in the Sept. 28 issue of Circulation.
Researchers for the CARISMA trial, led by Poul Erik Bloch Thomsen, MD, from Gentofte University Hospital, Copenhagen, Denmark, said that the lack of traditional ECG recording systems to document and confirm asymptomatic and symptomatic arrhythmias has limited the field's knowledge about the incidence of cardiac arrhythmias after acute MI (AMI) in patients with depressed left ventricular ejection fraction (LVEF).
They noted that studies show a disparity between clinical arrhythmic event definitions and occurrence of true cardiac arrhythmias. Most documentation after AMI comes from Holter recordings at 24 and 48 hours, "leaving large gaps in the temporal knowledge of arrhythmia incidence in these patients."
They therefore sought to quantify arrhythmic events with an implantable cardiac monitor (ICM) (Reveal Plus, Medtronic) in 297 patients in the multicenter observational CARISMA trial.
Patients had a mean LVEF of 31 percent, received the ICM within a mean 11 days of the AMI and were followed-up every three months for an average of 1.9 years.
The device recorded bradyarrhythmias and tachyarrhythmias in 46 percent of the patients, 86 percent of which were asymptomatic.
Specifically, 27 percent of patients experienced new onset atrial fibrillation (AF), 9.8 percent had high-degree atrioventricular (AV) block, 6.7 percent had sinus bradycardia, and 13 percent had non-sustained ventricular tachycardia.
The most powerful predictor of cardiac death was high-degree AV block.
The device recorded high-degree AV block in 29 patients, eight of whom had symptoms at the time of the event. The total number of high-degree AV block episodes was 124, corresponding to 14 percent of all arrhythmias, with 48 events occurring during the daytime (7 a.m. to 11 p.m.), but only 20 were symptomatic
"For the first time, there are data showing that continuous long-term monitoring allows detailed insight into post-AMI arrhythmias," Thomsen said. "Additional information about post-AMI patients can help physicians determine appropriate medical intervention, such as an implantable cardioverter-defibrillator [ICD], pacemaker or modified drug therapy."
Exploring second- to third-degree AV block further, researchers found that 10 of the 11 deaths were attributable to cardiac causes. A pacemaker was implanted in 10 of the patients with AV block, and three received an ICD. The 10 cardiac deaths were distributed evenly among patients with and without implanted devices.
"Although second- to third-degree AV block was frequent in patients with all causes of death, it was particularly frequent in patients dying of nonarrhythmic causes (57 percent)," according to the study.
Of the 13 patients receiving a pacemaker or ICD, five later died of cardiac causes, including three from sudden death. However, cardiac death occurred in five of the 16 patients not implanted with a therapeutic device, with only one sudden arrhythmic death, "suggesting that a pacemaker or ICD would not have prevented death in the majority of these patients."
The authors said, "It is hypothesized that bradyarrhythmias may reflect more advanced structural heart disease in which right ventricular pacing may even be harmful to cardiac function."
The device was implanted subcutaneously with local anesthesia in the left parasternal area five to 21 days after the AMI. It is designed to continuously monitor the ECG for up to two years. Storage of the ECG can be initiated manually or is triggered automatically when arrhythmic events fulfill preprogrammed cutoff criteria.