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Imaging in Cardiomyopathies

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Classification Overview

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Imaging Modalities: Role Summary

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1. Hypertrophic Cardiomyopathy (HCM)

Chest X-ray

• Often unhelpful in early disease
• Concentric hypertrophy may produce a rounded third left cardiac contour (different from aortic stenosis/hypertension which cause similar but distinguishable appearance)

Echocardiography (Primary Modality)

• M-mode: measures IVS and posterior wall thickness; IVS:posterior wall ratio >1.3 is diagnostic
• B-mode: asymmetric septal hypertrophy (ASH); apical/midventricular/mass-like variants
• Doppler: LVOT obstruction in 25% due to systolic anterior motion (SAM) of mitral valve (Venturi effect); rest gradient or provokable gradient; impaired diastolic function (reduced E wave, E/A equalisation)
• Limitation: apical forms near the low-frequency probe, poor acoustic window

Cardiac MRI (Gold Standard for Tissue Characterisation)

• Cine MRI: precise wall thickness measurement; all hypertrophy patterns visible; accurate LV mass quantification; RV involvement quantified
• Late gadolinium enhancement (LGE): PATHOGNOMONIC pattern = intramural fibrosis with selective septal enhancement and relative sparing of the subendocardial layer (distinguishes from MI where enhancement is subendocardial/transmural)
  • Also: enhancement at anterior and inferior septal insertion points (RV insertion sites)
  • Patchy large intramural foci in severe cases
• Prognostic value of LGE: Fibrosis on MRI predicts ventricular arrhythmias, sudden cardiac death (<40 years), and progression to HF (>40 years)
• T1/T2 mapping: quantitative tissue characterisation; can detect diffuse fibrosis not seen on LGE

Cardiac CT

• Accurate wall thickness information at very low dose (1-3 mSv)
• Useful when MRI is contraindicated (pacemaker, claustrophobia)
• Can exclude coronary artery disease simultaneously

Special Variants of Hypertrophic Phenotype

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2. Dilated Cardiomyopathy (DCM)

Chest X-ray

• Cardiomegaly - cardiothoracic ratio >0.5
• Pulmonary venous congestion / pulmonary oedema in advanced disease
• Pleural effusions

Echocardiography

• Dilated LV with reduced EF (globally hypokinetic)
• Spherical LV shape
• Functional mitral regurgitation (dilated annulus)
• Diastolic dysfunction pattern
• LV thrombus detection (especially at apex)

Cardiac MRI

Cardiac CT

• Coronary CT angiography to exclude ischaemic cause (now first-line in many centres)
• LV dilatation on 4-chamber views
• Myocardial thinning at infero-apical segments in ischaemic DCM

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3. Restrictive Cardiomyopathy (RCM)

Chest X-ray

• Frequently unremarkable in early stages
• Advanced: left atrial enlargement, signs of elevated pulmonary venous pressure (similar to mitral stenosis)

Echocardiography

• Normal-sized or minimally enlarged ventricles with enlarged atria
• Normal or mildly decreased EF
• In Loeffler/endomyocardial fibroelastosis/carcinoid: endocardial thickening visible
• Doppler: elevated early diastolic velocity (E wave), short deceleration time, low atrial velocity (A wave) = restrictive filling pattern
• KEY challenge: must differentiate from constrictive pericarditis - similar Doppler findings

Cardiac MRI

• Gold standard for pericardial thickness measurement: >4 mm predicts constriction
• T1 and T2 weighted: tissue characterisation of infiltrative diseases
• LGE patterns by specific diseases:
  • Amyloidosis: diffuse global subendocardial enhancement; classic "zebra" or "leopard" pattern; rest T1 elevated; early blood-pool nulling
  • Sarcoidosis: patchy, non-coronary territory LGE; predilection for basal septum and lateral wall; T2 high in active disease
  • Haemochromatosis: LOW T2* signal (iron deposition causes susceptibility effect - myocardium appears dark on T2*)
• T1/T2 mapping: promising for differential diagnosis of infiltrative forms

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4. Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC)

Chest X-ray

• May be normal or show mild cardiomegaly
• RV enlargement in advanced disease

Echocardiography

• RV dilatation and dysfunction (reduced RVEF)
• RV wall motion abnormalities (focal akinesis, dyskinesis)
• RVOT dilatation
• Limitation: poor RV acoustic window

Cardiac MRI (Modality of Choice)

• Gold standard for ARVC diagnosis
• Key findings:
  • RV fatty infiltration: T1 high signal (fat) in RV free wall; however fat is also present in normal subjects, so presence alone is non-specific
  • RV dilatation and dysfunction: reduced RVEF, increased RVEDV
  • Regional wall motion abnormalities: focal akinesia, dyskinesia, or aneurysm of the RV free wall (triangle of dysplasia: RV inflow, outflow, and apex)
  • LGE: fibrosis in RV wall; LV involvement in advanced cases
  • Task Force Criteria (2010): structural/functional abnormalities on MRI are part of major and minor diagnostic criteria

Cardiac CT

• Can detect fatty infiltration in RV wall
• Structural assessment if MRI contraindicated

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5. Myocarditis (Inflammatory Cardiomyopathy)

Echocardiography

• LV systolic dysfunction (regional or global)
• Pericardial effusion suggests inflammatory process
• Non-specific; cannot provide tissue diagnosis

Cardiac MRI - Lake Louise Criteria (Cornerstone)

• Easily distinguishable from MI (subendocardial/transmural, follows coronary territory)
• In Takotsubo CMP: LGE is typically absent - key differentiator

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6. Takotsubo (Stress) Cardiomyopathy

• Echo/CMR: Apical LV ballooning with hypercontractile basal segments (reverse apical ballooning pattern in atypical forms)
• LGE: Characteristically absent (no necrosis - distinguishes from STEMI and myocarditis)
• CMR: T2 elevation in apical segments (oedema); resolves with recovery
• Coronary angiography: normal coronaries

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7. LV Non-Compaction (LVNC)

• Echo/CMR: Excessive trabeculation in LV; ratio of non-compacted to compacted layer >2.3 (MRI criterion); typically apical
• CMR is superior for trabeculation quantification
• LGE may be present in trabeculated segments

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LGE Pattern Summary Table (High-Yield for Exam)

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Key MRI Sequences and What They Show

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Exam Pearls

1. CMR is the gold standard for tissue characterisation in all cardiomyopathies
2. LGE spares subendocardium in HCM - key distinction from MI
3. Myocarditis = subepicardial LGE laterally; Takotsubo = no LGE
4. Amyloidosis: global subendocardial LGE + high native T1 + early blood-pool nulling + "sparkling" echo
5. Haemochromatosis: low T2* (iron causes susceptibility artefact making myocardium dark)
6. ARVC: RV fatty infiltration + RV dilatation/dysfunction + CMR Task Force Criteria
7. Constrictive pericarditis vs RCM: pericardial thickness >4 mm on CT/MRI favours constriction
8. DCM ischaemic vs non-ischaemic: subendocardial LGE in coronary territory = ischaemic; mid-wall septal LGE = non-ischaemic
9. Cardiac CT provides coronary anatomy + wall thickness at low dose; used when MRI contraindicated or to exclude ischaemic cause in DCM
10. Lake Louise Criteria require ≥2 of 3 (T2, EGE, LGE) for CMR diagnosis of myocarditis

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