Magnetocardiograms in Clinical Medicine: Unique Information on Cardiac Ischemia, Arrhythmias, and Fetal Diagnosis

Abstract

Cardiac diseases are the leading cause of death in population. Diagnostic tests to detect cardiac dysfunction at an early stage of the disease are desirable. The major focus has been centered on tests evaluating the perfusion of the heart with imaging techniques or detecting alterations in electrical or mechanical function of the heart. The heart generates magnetic fields that can be detected by body surface mapping utilizing super conducting quantum interference device sensors giving magnetocardiograms (MCGs). The advantages of MCG over traditional electrocardiograms (ECGs) are increased sensitivity to small signals and lack of conductivity in body tissues, presentation of direct component signals and primary currents. This review will highlight the basic principles and recent advantages of MCGs, and the application of MCG in clinical diagnosis, especially in cases whose ECGs are non-diagnostic or not specific, such as detecting baseline shift in ischemic heart disease, noninvasive His potential recording, detection of arrhythmic mechanism defining reentrant circuits vs non reentrant mechanism, diagnosis of fetal arrhythmias and prolongation of QT interval. Areas of future basic and clinical research are also discussed. (Internal Medicine 44: 1-19, 2005)

Magnetocardiography in Early Detection of Electromagnetic Abnormality in Ischemic Heart Disease

“…MCG and ECG differ in the concept of the baseline or zero level. 18) One reason is that direct currents are filtered in ECG but not in MCG. The ECG baseline is determined as the PR segment 19) or the TP segment, 20) while the MCG baseline is determined on the absolute scale measured by SQUID sensors.…”

“…18) In addition, high time resolution of MCG (less than 5 ms) make visualization of the macro-reentrant circuits or microexcitations of atrial fibrillations, flutters, and atrial tachycardia possible. 38,39) In normal heart, the current arrow map during ventricular repolarization exhibits the single current pattern which indicates a leftward, inferior direction 40,41) (Figure 12).…”

Contactless magnetocardiographic mapping in anesthetized Wistar rats: evidence of age-related changes of cardiac electrical activity

“…Multichannel MCG mapping measures the magnetic fields (MF) generated by cardiac activation currents, with minimal distortion due to the shape and conductivity of the lungs and torso (20,28). The advantages of contactless MCG mapping are as follows: 1) the ability to study conscious animals without movement artifacts (65), 2) the potential to provide diagnostic information not revealed by ECG (1,29,36,37,41,43,44,51,54,62,64,69,71,74,75), 3) the fixed-sensors geometry (42), which minimizes errors in localization of intracardiac sources (30) and three-dimensional electroanatomic imaging of arrhythmogenic phenomena (77), and 4) the localization of VR heterogeneities associated with areas of myocardial injury (50).…”

ICDs and Risk Stratification in Magnetic Field Imaging

“…Because of this unprecedented expansion of ICD implantations, that only in few cases (between 21 to 35%) (Bardy et al, 2005) leads to an appropriate therapy (arrhythmic events followed by a shock), there is a continuous interest in a non-invasive predictor for risk-stratification (refer to section 2). Within the last years, a new methodology is gaining interest in clinical use: Magnetic Field Imaging (MFI) / Magnetocardiography (MCG) (Yamada & Yamaguchi, 2005). Korhonen et al (Korhonen et al, 2006) have performed a pioneer clinical study analyzing the intra QRS-fragmentation in averaged MCG/MFI data (for a mathematical description of the method refers to (Link et al, 1994) and (Mueller et al, 1999)), after attempts made using the high frequencies components of the QRS as marker of risk both in Electrocardiography (ECG) (Cain et al, 1990) and MCG (Leder et al, 2000).…”