Magnetocardiography

Magnetocardiography (MCG) is a noninvasive method for recording the magnetic fields generated by the heart's electrical activity. The magnetic signals reflect currents flowing in the myocardium during depolarization and repolarization. Because magnetic fields are less distorted by the conductive tissues of the chest than electric potentials, MCG can provide a direct, time-resolved view of cardiac electrophysiology, though the signals are extremely small and require sensitive instruments. Typical cardiac magnetic fields at the body surface are on the order of tens to hundreds of picoTesla.

Measurement is performed with arrays of ultra-sensitive sensors, most commonly superconducting quantum interference devices (SQUIDs) housed in a magnetically shielded room, often with gradiometer configurations to suppress external noise. More recently, optically pumped magnetometers (OPMs) operating at room temperature have been explored as a portable alternative. The patient remains still during acquisition; recordings are typically synchronized with ECG, which helps with interpretation and localization.

Applications include assessment of cardiac rhythm disorders, evaluation of ischemia and other myocardial conditions, and in research settings for studying conduction and repolarization. Fetal magnetocardiography (fMCG) uses similar principles to monitor fetal heart rate and rhythm, aiding diagnosis of fetal arrhythmias and hypoxia. MCG is usually a supplementary tool to ECG and echocardiography, rather than a standalone diagnostic test.

Limitations include high cost, need for specialized shielding and cryogenic or room-temperature sensors, limited accessibility, and challenges in precise spatial localization due to the inverse problem. Ongoing work aims to improve sensor technology, data analysis methods, and standardization to widen clinical adoption.