Cardiac magnetic resonance imaging (cardiac MRI, or CMR) is an advanced imaging technique that provides detailed pictures of the heart’s structure, function, and tissue characteristics without using ionising radiation. It is one of the most informative investigations available in cardiology and plays an important role in diagnosing the cause of cardiac arrest and guiding ongoing management.
What cardiac MRI can show
Unlike an echocardiogram, which primarily shows structure and movement, cardiac MRI can:
- Precisely measure the volumes and pumping function of both ventricles
- Identify areas of scarring or fibrosis within the heart muscle (using a technique called late gadolinium enhancement, or LGE), which are common substrates for dangerous arrhythmias
- Detect inflammation of the heart muscle (myocarditis)
- Identify fatty infiltration of the right ventricular wall (relevant in ARVC)
- Characterise cardiomyopathies in detail, including hypertrophic cardiomyopathy and dilated cardiomyopathy
- Assess for signs of previous heart attacks not visible on other tests
After cardiac arrest
In survivors where the cause of arrest is not clear from initial investigations, cardiac MRI often provides crucial information. It may reveal myocarditis, subtle cardiomyopathy, or areas of scarring that explain the arrhythmia, even when echocardiogram and coronary angiography are inconclusive.
ICD compatibility
Most modern ICDs and pacemakers are MRI-conditional (safe under specific conditions) rather than MRI-incompatible. Patients with devices should always inform the MRI team, and scans are carried out according to the device manufacturer’s protocol. Older, non-conditional devices may preclude MRI scanning.
« Back to Glossary Index