Cardiac magnetic resonance imaging can identify iron deposition and may predict ventricular arrhythmia risk in patients with chronic myocardial infarction (MI), according to research published in Circulation: Cardiovascular Imaging.
Sudden cardiac arrest, usually caused by malignant ventricular arrhythmia (mVA), is the leading cause of death in the United States. More than half of sudden cardiac arrest victims have chronic MI, but the substrate that causes mVA to develop in chronic MI is unknown.
Risk predictors for ventricular arrhythmia such as infarct size, type of infarction, infarct transmurality, gray-zone or border-zone signal, surviving bundles, and surface electrocardiogram (ECG) parameters, have all been investigated. While these are accurate predictors for mVA compared with conventional left ventricular ejection fraction (LVEF), the arrhythmic substrate is complex. Based on previous evidence, iron deposition in the myocardium may in fact be arrhythmogenic.
“There is a critical need to develop and validate novel approaches for ventricular arrhythmia risk prediction incremental to the assessment of left ventricular function,” the researchers wrote.
They conducted a previous study on cardiac magnetic resonance imaging (MRI) with 18 canines, 9 of whom tested positive for hypointense cores (HIC). Researchers analyzed late gadolinium enhancement (LGE) image slices and found that approximately 40% were positive for MI. Based on the cardiac MRI results and histological validation studies, the researchers concluded that the positive HIC regions in balanced steady-state free precession images in chronic MI resulted from iron depositions.
The current human retrospective observational study examined 94 patients with chronic MI who were prescribed an iron-sensitive cardiac MRI sequence to determine the values of HIC in balanced steady-state free precession. All patients underwent cardiac MRI before receiving an implantable cardioverter defibrillator (ICD). Device follow-up visits were performed at 1, 3, and 6 months after implantation.
Nineteen patients had a cardiovascular event within a median of 249 days after their ICD placement. Only 1 of those patients was negative for HIC, and it was the HIC-positive chronic MI regions that were associated with the iron depositions. Of the 19 patients, 11 received an appropriate shock, 3 received antitachycardia pacing for sustained ventricular tachycardia, and 5 died from sudden cardiac death, one of whom died with advanced heart failure.
The data showed that only LVEF and HIC were statistically-significant, independent predictors of iron deposits. The researchers used a receiver operating characteristic curve analysis and found that the accuracy of prediction improved when HIC was added to the LVEF. The area under the curve was 0.87 when HIC was added to LVEF, whereas the curve for LVEF alone was 0.68.
Infarcts with iron deposits had worse remodeling, prolonged iron-driven inflammation, and altered electrophysiological parameters compared to infarcts without iron deposits. The researchers concluded that hemorrhagic acute MI could influence the development of chronic ventricular arrhythmia.
“This is a hypothesis-generating study, which provides sentinel evidence that HICs on iron-sensitive [cardiac MRI] may be a powerful predictor of mVA in patients with chronic MI,” the authors concluded.