What Exactly Does MCG Measure?

Published on
March 14, 2024
Ryan Yoo
Chief of Staff

In 1963, researchers Gerhard Baule and Richard McFee used two extremely large coils placed over a patient’s chest to record the first known measurement of the magnetic fields produced by electrical currents in the heart. This single event would mark the start of what would later come to be known as the field of magnetocardiography (MCG).

Magnetocardiography is a noninvasive and typically no-contact imaging method that involves the interrogation of the heart’s electrical activity through the measurement of the tiny magnetic fields generated by intracardiac currents during the heart’s typical pacemaking activity.

This is the same activity that generates surface electric field potentials measured by a standard 12-lead electrocardiogram (ECG). However, in contrast to ECG, MCG signals are undistorted by conductive tissue noise and are highly sensitive to tangential and vortex currents – the very same currents induced by ischemic extracellular injury.

Rather uniquely, MCG has demonstrated an ability to detect weak electrophysiological changes that are otherwise invisible to ECG, such as deviations in depolarization and repolarization which are characteristic of early-stage ischemia and which would not typically appear as interpretable deviations in the ST-segment as measured by ECG. Even more interestingly, several contemporary studies demonstrating this sensitivity have done so on patients kept at rest, demonstrating that MCG’s ability to interrogate the weak electrophysiological changes associated with earlier stage ischemia does not require the induction of hyperemia for diagnostic accuracy the same way that measurement of perfusion changes does. Other contemporary studies of MCG have even demonstrated a superior sensitivity for detecting ischemic myocardium in both stable CAD and suspected ACS patients when compared to either ECG or other well-understood noninvasive imaging modalities, include echocardiography and nuclear imaging.

Essentially, MCG has been demonstrated to perform remarkably well as a functional diagnostic for evaluating heart disease based on electrophysiology, in contrast to traditional imaging methods based on the evaluation of perfusion or known anatomical markers of disease.

Additionally, MCG’s ability to perform this interrogation at rest, without the need for radiation, and at a significantly higher speed (e.g., the typical CardioFlux MCG scan is just 90 seconds long) suggests MCG could have several impactful applications across the spectrum of ischemic heart disease, inclusive of both stable and acute presentations.

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