Magnetic Field Map Orientation in Patients after ST Elevation Myocardial Infarction

Abstract

Magnetic field map (MFM) orientation has been successfully applied in a number of studies investigating patients with coronary artery disease. In these patients, the degree of deviation of MFM orientation from normal values is dependent of the severity of the disease. In this work we examine MFM orientation in a large sample of patients who had just suffered acute ST Elevation Myocardial Infarction (STEMI) with successful interventional therapy. Ejection fraction (EF) and the presence of microvascular obstruction was assessed with cardiac MRI. Magnetocardiograms were obtained for 3 minutes in 83 STEMI patients and 31 age- and gender-matched healthy subjects using a 61 channel biomagnetometer. For each subject, the signals of ~50 beats of similar duration were averaged. MFM orientation was calculated for 420 points in the time-normalized QT interval and the percent deviations from the normal course, defined as the 95% confidence interval of the orientation values of the healthy subjects, was determined. The relative number deviations from MFM orientation was substantially higher for the STEMI subjects (35±18% vs. 4±7%, p<0.001). Sensitivity / specificity values were high, with an area under the receiver operating characteristic curve of 95% (p<0.001). Within the patient group, the % deviation was significantly higher in subjects with low EF (p<0.05), with three affected vessels (p<0.005) and with microvascular obstruction (p<0.05). Also, comparing patients with anterior and posterior infarction, orientation deviated less in the positive and more in the negative direction for the former group (p<0.001, p<0.05). The results demonstrate that MFM orientation is significantly changed after acute STEMI and that these changes can be associated with severity of the infarction. Furthermore infarct localization affected the direction of the deviation from normal orientation. MFM orientation may thus be useful in monitoring patients after acute myocardial infarction.