Science and History of Magnetocardiography
Magnetocardiography (MCG) is a technique to measure the magnetic fields produced by electrical activity in the heart. By measuring the magnetic fields through a multichannel sensor array placed over the chest, a map of the magnetic field can be constructed using mathematical algorithms.
Cardiac signals – Electric (ECG) vs. Magnetic (MCG)
Electric signals traditionally measured through the electrocardiogram (ECG) are influenced by the differently conductive tissue of the body and varying resistance of the skin before they can be recorded. Therefore, the differences in the electric potentials that are recorded by the ECG are directly dependent on the inhomogeneity and geometry of the thorax.
Magnetic signals however, travel through the body almost without disturbance. These signals travel through the thorax, which is essentially treated as a transparent volume conductor. The magnetic signals are vector-based measurements, unlike an ECG’s scalar measurements, which means the magnetic signal inherently possesses clinically useful information for an advanced and more accurate cardiac diagnosis.
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Use of Magnetocardiography
The principle of magnetocardiography has been extensively studied for over 30 years, both from a physics and clinical usefulness perspective. Historically, the magnetic signals were recorded through the use of highly sensitive magnetic sensors, Superconducting Quantum Interference Devices (SQUIDs), which are cooled down to 4 K (-269 °C) with liquid helium; these systems would typically require specially magnetically shielded rooms for optimal results. A limited number of these systems have been installed throughout the world, but predominantly in Europe and East Asia. The expense and ongoing operational costs had limited the clinical implementation of the SQUID systems.
Clinical Application of Magnetocardiography
Magnetocardiography and the method of imaging the cardiac generated magnetic field into an intuitive map, can detect the onset of cardiovascular disease in a very early stage with high accuracy for both acute and asymptomatic patients.Below are four areas MCG has been and continues to be studied
- Early detection of Arrhythmia; Ischemia, Angina pectoris
- Kandori A, et al. A method for detecting myocardial abnormality by using a total current-vector calculated from ST-segment deviation of a magnetocardiogram signal. Medical and Biological Engineering and Computing. 2000; 38: 21-28.
- Kwong JS et al. Diagnostic value of magnetocardiography in coronary artery disease and cardiac arrhythmias: a review of clinical data. International Journal of Cardiology. Sept 2013; 167(5): 1835-42
- Direct diagnosis of heart function after myocardial infarction (MI) and surgery of heart transplantation.
- Wu YW et al. Usefulness of magnetocardiography to detect coronary artery disease and cardiac allograft vasculopathy. Circulation Journal: official journal of the Japanese Circulation Society. 2013; 77(7): 1783-90.
- Park J, et al. Validation of magnetocardiography versus fractional flow reserve for detection of coronary artery disease. Clinical Hemorheology and Microcirculation. 2015; 59: 267-81
- On-going monitoring of patients with heart surgical intervention: Patients with a stent or who underwent a balloon dilatation; post bypass patients; post heart transplantation patients.
- Shin E, et al. Incremental diagnostic value of combined quantitative and qualitative parameters of magnetocardiography to detect coronary artery disease. International Journal of Cardiology. 2017; 228: 948-952.
- Bang W, et al. Repolarization heterogeneity of magnetocardiography predicts long-term prognosis in patients with acute myocardial infarction. Yonsei Medical Journal. Nov 2016; 57(6): 1339-1346.
- Detect the cardiac signal of an unborn child starting from the 4th month of pregnancy.
- Eswaran H, et al. Fetal magnetocardiography using optically pumped magnetometers: a more adaptable and less expensive alternative? Prenatal Diagnosis. Feb 2017; 37(2): 193-196.
- Cuneo BF, Strasburger JF, Wakai RT. The natural history of fetal long QT syndrome. Journal of Electrocardiology. 2016;49(6):807-813.
A True Non-Invasive Procedure
While other diagnostic tests such as nuclear/exercise stress tests or CT-angiograms (CTA) claim to be non-invasive procedures they still emit a form of energy on the body, such as radiation or magnetic energy to complete the procedure. Magnetocardiography systems have no contact with the surface of the human body and passively scan the magnetic fields generated by the heart’s electric activity. The procedure can be repeated without any negative effects for the patient, which gives the physician the opportunity to observe a patient’s progressive changes as needed.