What is the role of cardiac magnetic resonance imaging (CMR) in the assessment and management of adults with congenital heart disease (CHD)?

Role of Cardiac MRI in Adult Congenital Heart Disease

Cardiac MRI should be regarded as an indispensable facility complementary to echocardiography in specialized centers caring for adults with congenital heart disease, serving as the reference standard for ventricular quantification, comprehensive anatomic assessment, and tissue characterization. 1

Primary Clinical Applications

Anatomic Assessment

Cardiac MRI excels at comprehensive anatomic evaluation without the acoustic window limitations of echocardiography, providing unrestricted access to 1:

• Systemic and pulmonary venous connections (anomalous connections or obstruction) 1
• Right ventricular outflow tract and pulmonary arteries, including RV-PA conduits for stenosis or aneurysm 1
• Entire aorta for aneurysm, dissection, or coarctation assessment 1
• Branch pulmonary arteries and aorto-pulmonary collaterals 1
• Coronary artery origins and proximal course using cardiac-gated 3D SSFP angiography without contrast, though CT provides superior coronary detail 1, 2

Functional Quantification

CMR has emerged as the reference standard for biventricular volume and mass quantification, particularly critical when echocardiographic measurements are borderline or ambiguous 1, 2:

• Right ventricular volumes and ejection fraction, especially after tetralogy of Fallot repair where RV assessment is crucial for surgical timing 1, 2
• Pulmonary regurgitation quantification using through-plane velocity mapping 1
• Shunt quantification by measuring flow in ascending aorta and pulmonary trunk 1
• Pressure gradients across stenotic regions using phase-contrast techniques 2

Tissue Characterization

CMR uniquely provides direct tissue characterization beyond anatomic imaging 2:

• Myocardial fibrosis detection in both ventricles using late gadolinium enhancement, though RV-LV insertion point enhancement is non-specific when ventricles are hypertrophied or dilated 1, 2
• Viability and perfusion assessment in patients with coronary anomalies or acquired coronary disease 1, 2
• Tissue characterization for fat, iron loading, and other infiltrative processes 1

Specific Lesion Applications

Post-Tetralogy of Fallot Repair

CMR is particularly valuable for assessing 1:

• RV and LV function with regional wall motion abnormalities
• Pulmonary regurgitation severity
• RVOT obstruction or conduit stenosis
• Residual shunting
• These measurements directly inform pulmonary valve replacement timing

Fontan Circulation

Comprehensive assessment includes 1:

• Cavo-pulmonary connections using transaxial cine stacks
• Branch pulmonary arteries and pulmonary veins (which can be compressed by dilated right atrium)
• Ventricular function and atrioventricular valve competence
• Systemic-to-pulmonary collateral flow quantification
• Intra-atrial thrombus detection

Aortic Coarctation

CMR provides 1:

• 3D visualization of arch geometry and any aneurysm formation
• Collateral vessel assessment by comparing flow proximal to stenosis versus at diaphragm level
• Diastolic flow prolongation beyond coarctation indicating significant stenosis
• Pre-intervention planning for balloon dilatation or stenting

Complex Congenital Heart Disease

For operated or unoperated complex lesions, use contiguous transaxial and coronal cine stacks to establish 1:

• Sequential segmental anatomy (atrial situs, ventricular morphology, great vessel connections)
• Morphologic RV versus LV identification (moderator band and coarse trabeculations arise from RV septum only)
• Anomalous vessels, shunts, and stenoses
• Abdominal situs and possible polysplenia

Clinical Implementation Algorithm

When to Order CMR

Order CMR when 1, 2:

1. Echocardiographic measurements are borderline or ambiguous for ventricular volumes, ejection fractions, or valvular regurgitation that are critical to management decisions 1

2. Baseline assessment is needed - many ACHD patients benefit from at least one CMR study to provide baseline for future reference and identify unexpected anomalies 1

3. Change is suspected during echocardiographic follow-up, particularly onset or progression of symptoms 1

4. Comprehensive pre-operative assessment is required before intervention or surgery 1

Follow-Up Intervals

Echocardiography remains suitable for routine follow-up, but serial CMR intervals should be 1:

• 3 years or more for most stable conditions 1
• Earlier restudy if symptoms progress or lesions are liable to rapid progression 1
• Intervals depend on condition risk, expected rate of change, and measurement accuracy at your center 1

Critical Technical Considerations

Contraindications and Limitations

Implanted pacemakers and defibrillators generally preclude CMR 1

For patients with eGFR <30 mL/min/1.73m², gadolinium should be avoided due to nephrogenic systemic fibrosis risk; use non-contrast sequences (gradient-echo cine imaging, phase-contrast techniques) instead 2, 3

For patients with eGFR ≥30 mL/min/1.73m², use Group II gadolinium agents at the lowest diagnostic dose 2, 3

Required Expertise

CMR studies in ACHD require Level 2 and preferably Level 3 training, including supervised interpretation of 150 adult congenital CMR studies with presence at 50 scans 1

RV volume measurements are time-consuming and require meticulous technique - tracing the RV boundary within the thin compact myocardial layer (rather than trabeculations) improves reproducibility, though semi-automated methods are acceptable if consistently applied 1

Longitudinal comparisons must use comparable acquisition and analysis methods - store contour data in a database for comparison at subsequent studies 1

Comparison with Other Modalities

CMR versus Echocardiography

Echocardiography remains the first-line imaging modality 1, 2, 4, but CMR is superior for 2, 4, 5:

• Right ventricular volume and function assessment
• Patients with poor acoustic windows (post-surgical, body habitus)
• Comprehensive great vessel evaluation
• Quantitative flow measurements

CMR versus CT

CT is preferred when 1, 4:

• CMR is contraindicated (pacemakers, defibrillators)
• Superior spatial resolution is required (aorto-pulmonary collaterals, coronary angiography)
• Metallic artifacts limit CMR imaging (stents, occlusion devices)

CMR is preferred for 1, 4, 5:

• Serial follow-up (no ionizing radiation)
• Tissue characterization
• Functional assessment with flow quantification
• Younger patients requiring lifelong monitoring

Common Pitfalls to Avoid

Do not rely on CMR alone for 1:

• Patent foramen ovale identification (echocardiography superior)
• Valve leaflet structural abnormalities and vegetations (echocardiography superior)
• Thin mobile structures (not well seen on breath-hold acquisitions)

RV-LV insertion point enhancement on late gadolinium imaging is non-specific when ventricles are hypertrophied or dilated and of doubtful clinical significance 1

Ferromagnetic occlusion devices in older Fontan patients can create artifacts precluding satisfactory CMR 1

Timing and distribution of contrast arrival in Fontan circulations requires special consideration - non-contrast 3D SSFP or leg vein injection may be preferable 1