Cardiac MRI — Med2Date

📋 Key Information Summary

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Cardiac MRI (CMR) is the gold-standard non-invasive modality for myocardial tissue characterisation, providing precise assessment of structure, function, viability, and infiltration.
Key sequences include cine imaging for function, T2-weighted imaging for oedema, and late gadolinium enhancement (LGE) for scar/fibrosis.
CMR is the reference standard for quantifying biventricular volumes, ejection fraction, and mass with high reproducibility.
LGE imaging is uniquely capable of differentiating ischaemic (subenducal/transmural) from non-ischaemic (epicardial/mid-wall) patterns of fibrosis.
It is the primary modality for diagnosing acute myocarditis, using Lake Louise criteria (oedema + LGE) and parametric mapping (T1/T2).
CMR viability assessment guides revascularisation decisions in ischaemic cardiomyopathy, with >50% transmural LGE predicting no functional recovery.
Indications include unexplained cardiomyopathy, suspected myocarditis, complex congenital heart disease, cardiac masses, and pericardial disease.
Absolute contraindications: non-CMR conditional pacemakers/ICDs, certain cerebral aneurysm clips, metallic ocular foreign bodies.
Gadolinium-based contrast agents (GBCA) are contraindicated in severe renal impairment (eGFR <30 mL/min/1.73m²) due to nephrogenic systemic fibrosis risk.
Australian access: primarily via public hospital radiology departments and specialised private cardiac imaging centres; MBS item 63310 for stress CMR.

Introduction & Australian Context

Cardiac Magnetic Resonance (CMR) imaging is a non-invasive, radiation-free modality that has evolved into the gold standard for myocardial tissue characterisation. It provides unparalleled assessment of cardiac structure and function, myocardial viability, infiltration, inflammation, and iron overload. In Australia, CMR is increasingly integrated into cardiology pathways, supported by specialised centres in tertiary hospitals and major private practices.

Its role is pivotal in diagnosing and managing conditions where echocardiography is limited, such as arrhythmogenic right ventricular cardiomyopathy (ARVC), cardiac sarcoidosis, and myocarditis. The ability to differentiate between ischaemic and non-ischaemic cardiomyopathy has significant therapeutic implications. Australian data indicate rising utilisation, particularly for myocarditis diagnosis and pre-ablation ventricular tachycardia (VT) substrate mapping.

Technical Principles & Sequences

CMR utilises a combination of sequences tailored to answer specific clinical questions. ECG gating and breath-holding or respiratory navigation are used to minimise motion artefacts.

Core Sequences

Sequence	Primary Purpose	Key Findings
Cine SSFP (Steady-State Free Precession)	Volumetric & functional assessment	Biventricular volumes, ejection fraction, mass, regional wall motion
T2-weighted (STIR or T2-prep)	Myocardial oedema/inflammation	High signal indicating acute injury or inflammation
Early Gadolinium Enhancement (EGE)	Hyperaemia/capillary leak	Supports diagnosis of myocarditis when combined with T2
Late Gadolinium Enhancement (LGE)	Fibrosis/scar/necrosis	Non-viable myocardium; pattern is diagnostically specific
Parametric Mapping (T1, T2, ECV)	Diffuse interstitial disease	Quantifies diffuse fibrosis (elevated ECV), amyloid (low native T1), iron overload (low T2*)

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Australian Note: Parametric mapping is available at most tertiary centres but not universally. Its use is expanding, particularly for detecting diffuse processes like Anderson-Fabry disease and cardiac amyloidosis.

Assessment of Cardiomyopathy & Myocarditis

CMR is the investigation of choice for unexplained cardiomyopathy. It provides aetiological diagnosis, prognostic stratification, and guides therapy.

Ischaemic vs. Non-Ischaemic Patterns

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Key Diagnostic Differentiator: LGE pattern. Ischaemic cardiomyopathy shows subendocardial or transmural enhancement in a coronary artery territory. Non-ischaemic patterns are typically epicardial, mid-wall, or patchy.

Myocarditis (Lake Louise Criteria)

CMR diagnosis of acute myocarditis requires a combination of tissue markers:

Criterion 1 (Oedema): Regional or global myocardial signal increase on T2-weighted imaging.
Criterion 2 (Injury/Necrosis): Non-ischaemic pattern LGE OR increased native T1/T2 values.
Diagnosis is considered likely if 2 of 2 criteria are met. Possible if 1 of 2 is met.

Specific Cardiomyopathies

Hypertrophic Cardiomyopathy (HCM): LV wall thickness ≥15 mm (≥13 mm with family history). LGE is common (patchy, often at RV insertion points). Identifies high-risk features for sudden cardiac death (extensive LGE >15% of LV mass).
Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC): CMR demonstrates RV dilatation, regional RV akinesia/dyskinesia, and fibrofatty infiltration (qualitative). 2010 Task Force Criteria include CMR parameters.
Cardiac Sarcoidosis: LGE in a mid-wall/epicardial pattern, often basal septal. Active inflammation may show oedema and patchy LGE.

Viability Imaging (Late Gadolinium Enhancement)

LGE-CMR is the most accurate method for assessing myocardial viability in patients with ischaemic cardiomyopathy and LV dysfunction. It directly visualises scar tissue.

Interpretation & Clinical Implications

Transmurality

0-25% Scar

Viable, hibernating myocardium.

Likely to improve function with revascularisation.

Transmurality

26-50% Scar

Mixed viability.

Possible recovery; clinical decision-making required.

Transmurality

>50% Scar

Non-viable, scarred myocardium.

No functional recovery expected post-revascularisation.

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Decision Point: In patients with LV ejection fraction ≤35% and >50% transmural LGE in akinetic segments, revascularisation is unlikely to improve LV function. Management should focus on optimal medical therapy and device therapy (ICD/CRT) as indicated.

Clinical Indications & Contraindications

Common Indications for CMR in Australia

Differentiation of ischaemic vs. non-ischaemic cardiomyopathy.
Suspected acute myocarditis (e.g., troponin rise with normal coronary angiography).
Assessment of suspected ARVC or HCM for risk stratification.
Evaluation of cardiac masses (thrombus vs. tumour).
Complex congenital heart disease follow-up (e.g., repaired Tetralogy of Fallot).
Quantification of aortic regurgitation/severity in aortic valve disease.
Viability assessment prior to revascularisation.
Pericardial disease (constrictive pericarditis).
Stress perfusion CMR for ischaemia detection (MBS Item 63310).

Contraindications

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Absolute Contraindications:

Non-MR conditional pacemakers or implantable cardioverter-defibrillators (ICDs).
Certain intracranial aneurysm clips (ferromagnetic).
Metallic ocular foreign bodies.
Cochlear implants (unless MR conditional).

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Relative Contraindications & Safety:

Gadolinium Contrast: Contraindicated if eGFR <30 mL/min/1.73m² (high risk of nephrogenic systemic fibrosis). Use macrocyclic agents preferentially.
Pregnancy: Generally avoided, especially in the first trimester. Use without contrast only if essential.
Claustrophobia: May require anxiolytic premedication or open-bore scanners where available.

Australian Access & Funding

CMR is primarily available in:

Public Tertiary Hospitals: Major metropolitan centres (e.g., Royal Melbourne, St Vincent's Sydney, Alfred Melbourne) and some regional centres.
Private Cardiac Imaging Providers: Concentrated in capital cities; wait times are typically shorter.
MBS Item 63310: Covers stress CMR for ischaemia assessment. Non-stress diagnostic CMR is often funded via hospital outpatient or public system grants.

Aboriginal and Torres Strait Islander Health Considerations

Access Disparity

Access to advanced cardiac imaging like CMR is severely limited for Aboriginal and Torres Strait Islander peoples, particularly in remote and regional communities. The nearest scanner may be thousands of kilometres away.

Disease Burden

Rheumatic heart disease (RHD) prevalence is significantly higher. CMR is valuable for assessing chronic rheumatic valvular disease and associated cardiomyopathy, but access barriers delay diagnosis.

Cultural Safety

The clinical environment must be culturally safe. Consider the need for family presence, gender-sensitive care, and clear communication about the procedure via Aboriginal Health Workers or Liaison Officers.

Funding & Pathways

State/Territory-funded patient-assisted travel schemes (PATS) are often required but are complex and underutilised. Telehealth consultations pre- and post-CMR can improve continuity of care.

📚 References

1. Kwong RY, Ge Y, Steel K, et al. Cardiac Magnetic Resonance Stress Perfusion Imaging for Evaluation of Patients With Chest Pain. J Am Coll Cardiol. 2019;74(14):1741-1754.
2. Ferreira VM, Schulz-Menger J, Holmvang G, et al. Cardiovascular Magnetic Resonance in Nonischemic Myocardial Inflammation: Expert Recommendations. J Am Coll Cardiol. 2018;72(24):3158-3176.
3. Australian Institute of Health and Welfare (AIHW). Rheumatic heart disease and acute rheumatic fever in Australia. Cat. no. CVD 86. Canberra: AIHW; 2020.
4. National Heart Foundation of Australia and Cardiac Society of Australia and New Zealand. Guidelines for the prevention, detection, and management of heart failure in Australia 2018. Heart, Lung and Circulation. 2018;27(10):1123-1208.
5. Gulati A, Japp AG, Raza S, et al. Absence of Myocardial Fibrosis Predicts Excellent Long-Term Survival in New-Onset Heart Failure. Circ Cardiovasc Imaging. 2018;11(10):e007722.
6. Petersen SE, Friedrich MG, Leiner T, et al. Cardiovascular Magnetic Resonance for Common Adult Diseases: Clinical Impact and Society Recommendations. JACC Cardiovasc Imaging. 2022;15(5):855-877.
7. Australian Government Department of Health. Medicare Benefits Schedule - Item 63310. Available at: http://www.mbsonline.gov.au
8. Ponikowski P, Voors AA, Anker SD, et al. 2016 ESC Guidelines for the diagnosis and treatment of acute and chronic heart failure. Eur Heart J. 2016;37(27):2129-2200.
9. Maron MS, Rowin EJ, Wessler BS, et al. Enhanced American College of Cardiology/American Heart Association Strategy for Prevention of Sudden Cardiac Death in High-Risk Hypertrophic Cardiomyopathy Patients. JAMA Cardiol. 2019;4(7):640-649.
10. RHDAustralia (RHD Australia). The 2020 Australian guideline for prevention, diagnosis and management of acute rheumatic fever and rheumatic heart disease (3rd edition). Darwin: Menzies School of Health Research; 2020.