What is Magnetocardiography

WHAT IS MAGNETOCARDIOGRAPHY (MCG)?

Background

It is an axiom that Electrical current always produces an associated magnetic field, and the electrical currents in the heart caused by depolarization-repolarization processes produce corresponding time-varying changes in the magnetic field around the heart.

Magnetocardiography is a noninvasive technique for recording local magnetic fields generated by the electrical activity of the heart. A magnetocardiogram (MCG) is nothing more than the recording of the heart’s electromagnetic signals, hence its electrical activity. The EKG and the MCG seek to measure the same electrophysiological event.

For over 100 years now, the first diagnostic test performed in the cardiac evaluation of a patient has been the electrocardiogram (EKG). It is inexpensive, non-invasive, and relatively portable so it can be used at the patient’s bedside, in the Emergency Room, or even carried by the patient ‘round-the-clock as in a Holter Monitor. But as ubiquitous and useful as the EKG is, it fails to provide complete information about the electrophysiological activity of the heart, and, at least for the detection of coronary artery disease, is grossly inadequate.

Electrical current in the heart is the driving force by which the heart operates, and the EKG is nothing more than a limited recording of the heart’s electrical activity. The waves that appear on an EKG primarily reflect the electrical activity of the myocardial cells, which comprise the vast bulk of the heart. Pacemaker cell activity and transmission by the conducting system are generally not seen on the EKG, because these events simply do not generate sufficient voltage to be recorded by surface electrodes. Nevertheless, perturbations in the normal electrical patterns as seen in an EKG allow one to diagnose many different cardiac disorders.

MCG

An MCG procedure does not require a large number of patient leads, contrast agents, or injected tracers as in Radionuclide or MR imaging. MCG senses magnetic fields, it does not create them. The local magnetic fields created by the electrical currents in the heart can be detected and recorded using extremely sensitive Superconducting Quantum Interference Device (SQUID) sensors, the most sensitive magnetic field sensors known. Recent progress in SQUID and related technologies now makes it possible to record MCG data (magnetocardiograms) in suitably chosen magnetically unshielded clinical/hospital environments. An array of multiple SQUID sensors placed at predetermined and fixed positions over the subject’s torso gives MCG the ability to measure depolarization/repolarization of the heart at multiple locations, without significant interference from extra-cardiac anatomical structures.