Mag·ne·to·car·di·og·ra·phy
[mag-ˌnēt-ō-ˌkärd-ē-ˈäg-rə-fē]
A medical imaging technique to measure the magnetic fields produced by the heart’s electrical activity using extremely sensitive devices.
First discovered in 1963, MCG is a medical imaging technique that measures the magnetic fields naturally generated by the electrical activity of the heart. The unique sensitivity of MCG enables physicians to detect and characterize even the smallest alterations in cardiac electrophysiology that may arise as a result of heart disease.
Timeline of MCG
Unfortunately, early versions of MCG devices were too bulky, expensive, and finicky to be useful in clinical practice, limiting their adoption to mostly academic institutions.
Genetesis’ CardioFlux MCG resolves these barriers by integrating the latest advances in sensing technology and machine learning to produce an MCG device requiring only a standard-sized room (without magnetic shielding) and a single standard outlet.
The most well-known output of MCG is the magnetic field map (MFM). An MFM appears as a 2D image that characterizes magnetic field intensity. The heart’s electrical conduction gives rise to the net current vector and corresponding magnetic dipoles, defined by the most positive and most negative magnetic field values captured.
During ventricular repolarization, a normal MFM should exhibit a singular current pattern that results in a single positive and negative pole, each appearing distinct and clearly defined.
In patients with functional ischemia, a multipolar pattern will often appear during repolarization, indicating heterogeneity and alterations in the amplitude and rate of action potentials in affected tissue.
MCG is believed to detect cardiac dysfunction early on in the ischemic cascade because of its sensitivity to changes in ion conduction and action potential. One of the major advantages of MCG is that magnetic fields are not distorted as they travel through tissue, unlike electrical currents that are directly measured using EKG. Additionally, MCG has demonstrated higher sensitivity to tangential and vortex currents which provide ischemia-rich information.
Several decades of research and multiple peer-reviewed studies around the world have clearly proven MCG’s ability to diagnose coronary artery disease (CAD), where MCG has demonstrated accuracy rivaling - and in some cases, even outperforming - current standard of care stress testing.
Emerging data from a new study conducted by Genetesis and presented at the ESC 2022 meeting in Barcelona demonstrated how MCG may have the ability to diagnose coronary microvascular dysfunction (CMD) in patients with ischemia and non-obstructive arteries (INOCA), a disease understood to be “invisible” to most forms of clinically available stress testing.
Like other modern imaging technologies, MCG has the potential to be far more than a single-purpose diagnostic. Here are three major areas where MCG has been and continues to be explored.
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MCG has demonstrated the potential to identify myocardial regions with compromised electric activity at rest in multiple studies in the past. It is theorized that this is possible due to MCG displaying significantly greater spatial resolution compared to ECG, where MCG is so sensitive to changes in the heart’s magnetic field that it can identify ischemic tissue or tissue predisposed to ischemia.
Stress-based MCG should theoretically offer enhanced detection of inducible ischemia in patients by giving physicians the ability to compare the heart’s magnetic field at rest versus during a controlled period of stress. Further research is needed to validate applications where stress-based MCG offers additional diagnostic value over rest-based MCG.
In contrast with ECG (which records electrical voltages across the skin to measure cardiac electrophysiology), MCG aims to measure cardiac electrophysiology by measuring the magnetic fields generated by the heart’s electrical pacemaking activity but does so without making physical contact with the patient (i.e. MCG is a contactless modality).
One of the major advantages of MCG over ECG is that unlike the electrical currents measured by ECG, magnetic fields are undistorted as they travel through tissue. MCG is also sensitive to tangential and vortex currents that are undetected by ECG.
MCG’s significantly increased resolution in mapping cardiac activity means MCG can be sensitive to conditions that are not easily detected in a clinically scalable way by ECG.
MCG is most easily understood as a functional imaging test, and not as an anatomic one, as it does not directly image any coronary arteries. Early data suggests that visual changes in the Magnetic Field Map of a patient may be associated with stenosis location and could be used to infer the location of an obstructed coronary artery or arteries. However, research into a proper clinical application for localization is currently ongoing.
Because of MCG’s demonstrated sensitivity to ischemia across multiple studies, MCG has clear potential as an efficient, high-throughput tool for initial ACS risk stratification and then further determination of the need for additional downstream testing. In the ED environment, where unit economics are most acutely felt, MCG could represent a significant source of cost-savings for the management of suspected ACS patients.
In outpatient scenarios, MCG could easily assess patients presenting with new onset chest pain (or similar symptoms), meaning it could be used for both risk stratification of angina as well as serial monitoring of changes in cardiac function over time.
Beyond the detection of ischemia across all forms and presentations of Ischemic Heart Disease, MCG has shown significantly unique potential for diagnosing arrhythmias, cardiomyopathies, and other congenital heart diseases.
Because the test effectively places zero burden – radiation or otherwise – on a patient, MCG could also be deployed as a rapid, serial scan intended to track chronic disease progressions and measure patient response to treatment uptake.
While MCG has clearly demonstrated diagnostic utility in each of these patient populations separately, additional research still needs to be done to determine if a single MCG scan can effectively distinguish between the two forms without the need for additional information.
The most recent study into MCG’s sensitivity to microvascular dysfunction, Genetesis’s own MICRO trial, produced great proof-of-concept data that MCG can be used to rule-in CMD in patients with angina once obstructive coronary artery disease has been ruled out (via CCTA or invasive angiography).