Nondipolar Content of Cardiac Magnetic Field Maps in Patients after ST Elevation Myocardial Infarction

摘要

Electrophysiological changes occurring in the context of coronary artery disease (CAD) have been investigated using magnetocardiography. Various approaches have been developed and studied which quantify different aspects of the magnetic signals and reconstructed magnetic field maps (MFM). In this work, we compare the coherence of MFM by determining their relative nondipolar content on the basis of the Karhunen-Loeve transformation in healthy subjects and patients with acute ST elevation myocardial infarction (STEMI). Magnetocardiograms were obtained for 3 minutes in 31 healthy subjects and 75 STEMI patients using a 61 channel biomagnetometer. For each subject, the signals of ~S0 beats of similar duration were averaged. Integral maps were calculated for 6 different segments of the QRST interval. For each segment 12 eigenmaps were constructed using Karhunen-Loeve transform. Nondipolar content was determined as percentage of the contribution of all eigenvectors beyond the third. The results showed that the nondipolar content of the MFM was generally increased in the patient group. Discriminatory power of each segment was assessed by the area under the curve (AUC) of the receiver operating characteristic. Results showed that the AUC was highest during repolarization: ST segment 74%, T wave 78% , terminal T wave 77% (p<0.001). Depolarization segments discriminated poorly (QRS, R peak: -50%). Furthermore, maps with dipolar content (maps 1-3) permitted excellent discrimination with AUCs > 90% for the T wave (p<0.001). The results indicate that the nondipolar content of MFM in patients with acute symptoms of CAD increases particularly during repolarization. However T wave coherence in the dipolar maps differed even more so between healthy subjects and patients with myocardial infarction. Principal component analysis of cardiac MFM using the Karhunen-Loeve transform may thus be helpful in the surveillance of patients with CAD.