Cardiomyopathies comprise a wide range of myocardial disorders that may be primary heart diseases or a feature of a systemic disease, and which may or may not have a genetic and/or familial component.¹ Cardiomyopathy is defined as a:

The key aim in the work-up of suspected cardiomyopathy is to identify a potentially treatable underlying cause, to risk-stratify the patient for prognostication, and to apply an effective therapeutic strategy. Besides evidence-based pharmacological therapeutic options, therapy includes consideration for an implantable cardioverter defibrillator (ICD), cardiac resynchronisation and orthotopic heart transplant.¹

Cardiovascular magnetic resonance (CMR) provides the opportunity to obtain key information during a single non-invasive study. Data on cardiac anatomy, function, tissue characterisation, coronary and microvascular perfusion and valvular structure and function in any selected orthogonal plane, independent of the patient habitus, can be safely acquired. The absence of ionising radiation adds to its safety. This safety feature includes intravenous contrast which allows repeated follow-up imaging, family screening and serial risk stratification.

Metallic implants and intracardiac devices (pacemakers and ICDs) represent the only absolute contraindications to CMR. However, this is being overcome with the increasing use of MR-compatible devices. Metallic objects in delicate positions (e.g. within the eye) continue to pose a problem as ferromagnetic objects may act as projectiles within the powerful magnetic field of the scanner and cause injury. Relative contraindications include claustrophobia, florid heart failure and clinical instability. CMR up to 3 Telsa is safe during all trimesters of pregnancy.⁸

Severe renal failure (glomerular filtration rate [GFR] < 30 mL/min) precludes the use of gadolinium owing to a small but tangible risk of nephrogenic systemic fibrosis, which is enhanced by concomitant heart failure (HF).¹ The limited availability of CMR scanners and CMR expertise are currently the most important limitations.

The imaging clinician’s first task is to obtain maximum information about the suspected diagnosis by evaluating clinical notes, operative notes, and previous investigations such as electrocardiograms (ECGs), echocardiography (echo), cardiac tomography and prior CMR studies.

After performing the anatomical and functional sequences to assess heart morphology and function, the following features should be identified to assist in optimising scan planning:⁹

CMR is considered as a Class I indication for global and regional LV and RV function, volume and mass quantification.^10,11 Indications include:

DCM refers to LV systolic dysfunction with concomitant LV dilation; RV dilatation may be present. In 50% of cases, the diagnosis remains unknown; up to 30% have a familial association to known genetic abnormalities.¹² Chronic myocarditis has been implicated in the aetiology of DCM.¹²

CMR provides accurate evaluation of biventricular EFs, volumes and mass assessment, and the pattern of LGE allows the exclusion of an ischaemic cause, typically subendocardial or transmural enhancement. LGE provides prognostic information and acts as a gatekeeper role to coronary angiography.¹³

In a large study with DCM and unobstructed coronary arteries, three LGE patterns were reported: no LGE in 59%, midwall and mainly septal LGE in 28%, and subendocardial ischaemic LGE pattern in 13%, probably on the basis of transient occlusion by non-obstructive unstable plaque or vasoconstriction.¹³

Other studies have shown additional LGE patterns that include epicardial LGE, patchy LGE and diffuse LGE.¹⁴ The finding of LGE in DCM is associated with increased risk of SCD, presumably arrhythmogenic.

Figure 1 and Figure 2 provide the representative imaging features of DCM.

LVNC is a rare congenital cardiac disorder owing to arrested embryogenesis and results in a ‘spongy’ appearance of the LV myocardium and apex, commonly involving the anterior and lateral walls and characterised by increased trabeculation and intratrabecular recesses in the myocardium.¹⁶ LVNC is associated with neuromuscular disorders and is complicated by heart failure, arrhythmia and thromboembolic events.¹ Diagnosis is achieved by measuring at end-diastole, the ratio of the noncompact myocardium over the compact myocardium. A value of 2.3 has a sensitivity of 80% and specificity of 99%.¹⁷

The absence of well-formed papillary muscles is a clue to the diagnosis.¹ LGE patterns include subendocardial, midwall and transmural enhancement.¹ LVNC is commonly associated with a DCM phenotype. Figure 3 demonstrates the imaging features of LVNC.

ARVC is a genetic desmosomal disease characterised pathologically by progressive RV myocyte loss and fibrofatty replacement.¹ In 75% of cases, the LV is affected and hence it can be misdiagnosed as DCM, especially in phenotypes with early and predominant LV involvement.¹ ARVC should be considered in all cases of unexplained RV dilation. Aborted SCD from arrhythmia is often the initial presentation.

ARVC task force criteria (TFC) forms the cornerstone of the diagnosis, and the 2010 revision has improved sensitivity for gene carriers with limited disease and patients with left-sided disease.¹⁸ The values for RVEF and EDV have been defined on the basis of comparison with normal patient data and divided into two categories.

HCM is the most common genetic cardiomyopathy, with an incidence of 1 in 500. It is also the most common cause of sudden death in the young, including athletes. Clinical findings and abnormal ECG findings associated with apical or asymmetrical septal hypertrophy, with or without dynamic LV outflow tract obstruction, is diagnostic. Pathologically, HCM demonstrates myocyte hypertrophy, disarray and fibrosis, manifesting in various genetic mutations.¹ The majority of individuals carrying an HCM genetic defect do not manifest the clinical expression at all times of their lives. Hence an unexplained mildly thickened LV wall may be consistent with a HCM-causing mutation. Making a diagnosis of HCM can be complicated in patients with aortic stenosis or hypertension.¹

Cine images allow the detection of LV wall thickness, especially at the apex, basal anteroseptal wall and posterolateral wall – regions that are difficult to visualise on echocardiography. However, a spectrum of LV wall thickening has been described.²¹ Myocardial crypts are additional typical findings. Apical aneurysms are associated with an increased risk for arrhythmia, thromboembolic events and progressive heart failure.²²

LGE is present in 80% of HCM, both patchy or diffuse scarring, the latter in areas of increased thickness typically and less commonly in regions of normal wall thickness.²³ Patchy LGE is typically midwall in thickened myocardium and commonly the RV-LV insertion points are also involved. In burnt-out HCM, the myocardium is thinned and has transmural LGE, mimicking ischaemic disease, but not in a coronary artery territory.

HCM without LGE has 100% event-free survival at 6-year follow-up; LGE > 5% of LV mass, septal wall thickness > 30 mm and AF are independent predictors of death and ICD discharges.²⁴

Left ventricular outflow tract (LVOT) obstruction and the presence of systolic anterior motion of the mitral valve can be quantified with velocity flow mapping and has been correlated with increased severity of hypertrophy, heart failure and poor outcome.²⁵

Figure 5 and Figure 6 demonstrate the imaging features of HCM.

Myocardial involvement in systemic amyloidosis is an important prognostic marker, often presenting as congestive heart failure in 50% of patients, and death occurring in less than 6 months in untreated patients. Early detected cases may respond to therapy, and exclusion of other causes is important for management.²⁶ Typical CMR findings include normal or reduced LV function, small LV cavity with homogeneous wall thickening, inconsistent RV involvement, biatrial enlargement, interatrial wall thickening, valve thickening, small pericardial effusions and pleural effusions. About 55% of patients with amyloidosis present with asymmetrical septal hypertrophy mimicking HCM.¹

LGE reflects the distribution of amyloid on histology with widespread subendocardial enhancement, giving the typical ‘zebra’ pattern and sparing the midwall of the septum. Other patterns are midwall (33%), and subepicardial (up to 20%).²⁷ RV free wall and interatrial septum LGE has been reported.¹

When amyloid fibrils accumulate in the myocardium, the wash-in and washout features of gadolinium are abnormal, with inability to null the myocardial signal. The rapid washout from the blood pool and high myocardial uptake results in a dark blood pool, owing to similar T1 values to the visualised myocardium.¹ To optimally visualise myocardial and blood pool kinetics in suspected amyloidosis, an inversion time scout is acquired at 5 min after contrast administration. LGE has a sensitivity of 86% for detecting amyloid. Identifying early abnormalities in patients with normal LV wall thickness is strongly related to the amyloid burden and predicted mortality risk.^28,29

Figure 7 demonstrates the representative imaging findings of amyloidosis.

Anderson-Fabry disease is a treatable X-linked disorder of lysosome storage, caused by partial or complete alpha galactosidase A deficiency which results in glycosphingolipid accumulation within the vessels and heart.³⁰ Concentric LV hypertrophy and cardiac fibrosis then leads to heart failure. CMR is used to evaluate LV function, wall thickness and scar detection. The typical LGE is inferolateral midwall enhancement which correlates well with histology and may serve as a substrate for electrical re-entry and SCD.³¹ Recently, T1 mapping has been shown to have a relative specific signature for conditions with a decreased T1 value, especially in areas of LGE.³² Six per cent of suspected HCM turns out to be Anderson-Fabry, with important implications for management. Anderson-Fabry is treated with enzyme replacement, with resultant improvement in LV function. The enzyme replacement is optimally utilised before fibrosis sets in. An unexplained LV hypertrophy, especially in young patients, should have Anderson-Fabry excluded.

Sarcoidosis is a multisystem granulomatous disease affecting the myocardium in 50% of cases, but only half of them are symptomatic.³³ HF and arrhythmia are the important presentations, and early identification allows medical therapy and ICD implantation.

CMR cine imaging facilitates the detection of wall thinning, regional wall motion abnormalities, ventricular dysfunction and pericardial effusion, whilst LGE CMR detects fibrosis. LGE is typically patchy, midwall or subepicardial, in an unpredictable manner, in the anteroseptal and anterolateral walls as well as in the RV free wall and RV side of the septum.³⁴ Sarcoid may mimic ischaemic disease with subendocardial or transmural patterns.³⁵ LGE acts as a guide to endomyocardial biopsy and improves after steroid therapy. T2W imaging may monitor disease activity with inflamed oedematous regions being highlighted.³⁴ Recently, T1 and T2 mapping has been shown to have a role in the assessment and monitoring of sarcoidosis.³⁶ Figure 8 demonstrates the representative imaging findings of sarcoidosis.

Cardiac siderosis is evident in transfusion-dependent anaemia and primary haemachromatosis. If chelation therapy is initiated early, the cardiomyopathy is reversible; but the diagnosis is often delayed owing to the late onset of symptoms. T2* imaging arises from local magnetic inhomogeneities that increase with greater iron deposition.¹ As myocardial iron increases, heart failure progresses and T2* times diminish so that all heart failure patients have a T2* value < 20 m/sec. The efficacy of chelation can also be monitored.¹ CMR has a significant role to play in the diagnosis and management of this disease.

CMR has increasing utility in providing diagnostic information in patients presenting with troponin-positive CPS with normal coronary arteries. It contributes to a diagnosis in 77% of patients, correcting a wrong diagnosis in 10% and changing therapy in 33%.³⁰ The main causes of CPS with normal coronary arteries are myocarditis, takotsubo cardiomyopathy, recanalised infarcts and the inflammatory phases of DCM, HCM and ARVC.

Systemic sclerosis is a connective tissue disorder affecting mainly the skin but also involving the lungs, kidneys and heart.⁴⁵ Myocardial fibrosis is a common finding at autopsy studies.⁴⁶ LGE manifests in a linear midmyocardial wall distribution at the basal and mid-ventricular levels. The development of clinical features indicates a poor prognosis, with a 5- year survival rate of 30%.⁹

Churg-Strauss is a rare small vessel syndrome with a poor prognosis. A subendocardial pattern of fibrosis in the absence of coronary artery disease is the typical pattern.⁴⁷ Associated features are normal myocardial function, apical obliteration and thrombus formation. Elevated blood eosinophils are commonly found and imaging features overlap with hypereosinophillic cardiomyopathy.

Rheumatoid arthritis (RA) is a chronic autoimmune disease primarily involving the synovium, but extra-articular manifestations include cardiac involvement which can lead to a 10-year reduction in life span, especially in young women. CMR has been shown to detect diffuse and focal myocardial fibrosis as well as inflammation in RA patients. In addition, myocardial fibrosis and inflammation correlates with a C-reactive protein (CRP) score of disease activity as well as with systolic and diastolic strain patterns.⁴⁸ Myocardial fibrosis is not related with disease duration and T1 mapping can provide a new biomarker of disease activity in the heart, beyond that provided by the standard sequences such as short T1 inversion recovery (STIR) and LGE.⁴⁸

Cardiac involvement in phaeochromocytoma is frequent and often persistent, manifesting as myocarditis, global LV dysfunction, subclinical systolic and diastolic dysfunction as well as focal and diffuse fibrosis. The myocardial effects of phaeochromocytoma have been shown to be beyond that of hypertension; catecholamine-induced cardiac toxicity is the likely cause, leading to inflammation, myocyte necrosis and fibrosis.⁴⁹

Peripartum cardiomyopathy is characterised by heart failure in the last trimester of pregnancy or first six post-partum months in previously healthy women. The cause is unknown and considered to be multifactorial. LGE is evident in the midmyocardium, mainly in the anterior and anterolateral segments. These features tend to regress over time as LV function improves.⁵⁰