Magnetocardiography as a Diagnostic Screening Tool for Myocarditis and Other Types of Cardiomyopathy

Inflammatory cardiomyopathy is one of the most common causes of sudden cardiac death in young adults, as it frequently remains undetected. Also, it is a common cause of heart failure, which may lead to circulatory collapse, requiring mechanical circulatory support or heart transplant. Some patients may require immunosuppression in addition to standard heart failure therapy. Early initiation of therapy is crucial for optimal outcomes.

Inflammatory disease of the heart muscle/inflammatory cardiomyopathy can be challenging to diagnose because it often requires expensive, time intense, and sometimes invasive testing, such as cardiac magnetic resonance imaging (MRI) and endomyocardial biopsies (EMB). As a result, there is an unmet clinical need for low threshold diagnostic screening in patients with suspected cardiomyopathy.

In this study the investigator's evaluate the diagnostic accuracy of magnetocardiography (MCG) in detecting inflammatory and other types of cardiomyopathy. Diagnostic accuracy will be compared to results from advanced imaging (cardiac magnetic resonance (CMR) imaging and/or positron emission computed tomography (PET-CT)) and where available to histology from endomyocardial biopsy/EMB.

CMR provides comprehensive structural and functional data while detecting consequences of inflammation, such as edema and late gadolinium enhancement. PET-CT detects the level of activity and the extent of inflammation through measurement of glucose metabolism. However, it cannot be applied frequently because of the associated radiation exposure. EMB is the gold standard for definitive diagnosis of inflammatory cardiomyopathy and is crucial for initiation of immunosuppressive therapy, as active viral infection should be excluded. However, the limited diagnostic yield due to sampling error and risk of potential complications limit its use to selected cases where there is a high suspicion that specific treatment may be necessary.

MCG is based on detecting the movement of ions in the myocardium. When an action potential in the heart is generated, it creates voltage changes and consequently an electromagnetic field. The strength and direction of this field are affected by the flow of ions both inside and outside the cells. Typically, the magnetic field produced by the heart ranges from from 10-15 to 11-11 Tesla.

MCG uses a superconducting quantum interference device (SQUID) to detect the electromagnetic field of the heart (up to 10*-15 Tesla). Measurements take place during the ascending T wave of the cardiac cycle. A vector score > 0.051 was determined to be pathologic in our recently published retrospective study. The investigator's will assesss diagnostic accuracy of MCG relative to cardiac magnetic resonance imaging (CMR) or positron emission computed tomography (PET-CT) and endomyocardial biopsy (EMB). Results from EMB take precedence over advanced imaging. Results from MCG will be independently assessed by two trained professionals blinded to the clinical diagnosis, with a third expert to adjudicate in cases of disagreement.

The MCG system utilizes an array of 64 highly sensitive magnetic sensors known as superconducting quantum interference devices (SQUIDs). These sensors are placed in a shielded environment to reduce interference from external electromagnetic sources. SQUIDs capture variations in the heart's magnetic field throughout the cardiac cycle and correlate these changes with the ECG. To filter out electromagnetic noise, several frequency filters are applied. The measurements provide a three-dimensional view of the magnetic field, which is used to generate a composite vector representing the primary electrical axis of the heart. In assessing inflammatory cardiomyopathies, the focus is on the vector associated with the T-wave of the action potential, specifically between the beginning of the T-wave on a 12-lead ECG to the maximum of the T-wave (T-beg-Tmax interval). A T-wave/MCG vector T-beg-Tmax value ≥ 0.051 has been identified as indicative of pathology, as demonstrated in our previous research (Brala et al, JAHA, 2023, PMID: 36744683).

The goal of this project is to validate the diagnostic accuracy of MCG for diagnosing inflammatory and other types of cardiomyopathy.

Inclusion criteria

• Patients with angina-like symptoms after exclusion of coronary artery disease

Exclusion criteria

• Presence of intracardiac metal devices and prior treatment with immunosuppressants