Right ventricular cardiovascular magnetic resonance imaging: normal anatomy and spectrum of pathological findings
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The right ventricle (RV) has been defined as the “forgotten chamber”, as its role in cardiac physiopathology has long been underestimated. Nevertheless, the RV is involved in a wide range of pathological conditions and its altered function may significantly affect the patient’s clinical status.
A selection of the most common cardiovascular magnetic resonance (CMR) features in a spectrum of pathological conditions is illustrated. Although its complex morphology, thin myocardium and trabeculated apex, RV can be accurately imaged by CMR, revealing its involvement in ischaemic and non-ischaemic heart disease. CMR has emerged as the pre-eminent modality in monitoring ventricular performance in congenital heart disease, pulmonary hypertension and cardiomyopathies. Arrhythmogenic right ventricular cardiomyopathy is a difficult diagnosis and the recently revised task force criteria confirmed a crucial role of CMR to increase diagnostic accuracy, by combining detection of RV dilation, regional wall motion and structural abnormalities. Moreover, a multiparametric approach of CMR is often necessary for delineation and characterisation of cardiac masses.
CMR, combining assessment of morphology, structure and function, has definitively emerged as the reference technique to evaluate a large variety of RV diseases.
• CMR offers unique advantages for imaging of many RV congenital, ischaemic and non-ischaemic diseases.
• Because of high reproducibility, CMR has a crucial role in decision-making for chronic RV pathology.
• The use of CMR increases detection of RV disease as infarction or arrhythmogenic cardiomyopathy.
KeywordsCardiovascular magnetic resonance Right ventricle Ischaemic heart disease Non-ischaemic cardiomyopathy Congenital heart disease
The right ventricle (RV) is involved in a wide variety of acquired and congenital heart diseases, even though the primary diagnostic focus is attributed to the left ventricle (LV) in most clinical conditions.  The importance of RV pathology and dysfunction has been highlighted in several recent publications in terms of impact on a patient’s prognosis and therapeutic management [1, 2, 3, 4].
Cardiovascular magnetic resonance (CMR) has emerged as the referenced standard technique for this purpose due to its unique capability in providing an accurate and reproducible assessment of function and tissue characterisation [5, 6].
Although trans-thoracic echocardiography is recommended as an initial imaging instrument, it has limited diagnostic capabilities for the assessment of RV due to its thin wall, peculiar morphology and the anterior position in the chest [7, 8].
The present pictorial review of the CMR features will illustrate RV anatomy and its range of various pathological conditions, thus leading to a more prompt recognition of disease.
All CMR exams were performed with a 1.5-T unit (Avanto; Siemens, Erlangen, Germany) with an eight-element phased-array coil.
The standard CMR protocol included T2-weighted black-blood short-inversion time turbo spin-echo imaging (T2WI), cine balanced steady-state free-precession sequences (cine SSFP) and T1-weighted contrast-enhanced inversion recovery segmented gradient echo sequence (LGE-T1WI) acquired 10–15 min after the intravenous administration of 0.2 mmol/kg gadobenate dimeglumine (Gd-BOPTA) for the evaluation of the late gadolinium enhancement (LGE) (see the online-only “Electronic supplementary material” for details).
Morphological T1-weighted TSE black blood sequences were added to the above protocol only for specific indications (e.g. morphology assessment and tissue characterisation in suspected arrhythmogenic right ventricular cardiomyopathy [ARVC]).
Flow measurement using velocity-encoded phase-contrast technique is a pre-eminent strength of CMR, enabling the detection and quantification of any valvular, vessel or conduit stenosis or regurgitation, whose main application is in the assessment of congenital heart disease.
Due to the complex anatomy of the RV, a combination of imaging in different cardiac planes is always helpful to better depict cardiac structures and therefore all sequences were performed on short axis, four-chamber and RV inflow-outflow views.
Normal anatomy of right ventricle
Recognising typical features of each cardiac chamber, in particular the ventricles, is necessary to interpret cardiac morphology, which may not be straightforward in some pathological conditions such as complex congenital heart diseases.
Chordal attachment of septal leaflet of tricuspid valve to the ventricular septum (never present in LV anatomy)
Presence of the moderator band, a muscular structure connecting the apical ventricular septum with the apical part of the RV free wall, involved in the cardiac electrical conduction system
“Crista supraventricularis”, a ridge separating the infundibulum and the inlet part
A trabeculated RV apex
Notably, there is no muscular or chordal structural inserts on the septum in LV; thus the moderator band and tricuspidal chordal attachment may be very helpful in distinguishing the morphological RV from the LV in congenital malformation.
Conversely, the interventricular septum shape and lateral wall thickness are not reliable features in defining the morphology of the RV.
In a normal subject, the chamber equals the LV in volume while the ventricular wall and trabeculations are substantially thinner than those of the LV (RV wall thickness: 3–5 mm), reflecting the different pressure regimen.
Congenital heart disease
The RV is often abnormal in congenital heart disease, in both isolated and complex malformations.
In this clinical setting, CMR has rapidly become the standard reference, whereas echocardiography suffers a lack of optimal acoustic window , particularly in postoperative patients, and CMR is independent of geometrical assumptions.
CMR has become a valid and comprehensive tool to define the anatomy, to assess bi-ventricular function  and haemodynamics, and to measure blood-flow by using phase contrast technique. Information provided by the exam can play a crucial role either in establishing the need and type of treatment or during follow-up after correction. For example, assessing the haemodynamic outcome after surgery requires a reproducible and accurate assessment of ventricular function as clinical decisions are usually based on a change in serial measurements rather than a single absolute value .
Tetralogy of Fallot
ToF is a complex malformation characterised by four heart defects, including ventricular septal defect, an overriding aorta, PS and RV hypertrophy.
The disease is commonly repaired by closure of the ventricular septal defect and correction of the RV outflow tract stenosis with patches or valvotomy, resulting in a distortion of anatomy.
CMR is commonly required to rule out post-repair complications which variably may consist of residual atrial and/or ventricular septal defect, akinesis or dyskinesis of the right ventricular outflow tract, outflow patch aneurysm and fibrosis of RV free wall or pulmonary artery stenosis [12, 13, 14, 15].
Pulmonary valve regurgitation is a nearly universal complication, accurately and reliably quantified by CMR using velocity-encoded phase-contrast technique, the degree of which has been demonstrated to be related to RV impairment, dilation or hypertrophy .
Velocity-encoded phase-contrast technique may also be useful to evaluate the trans-stenosis pressure gradient, by measuring peak velocity, when stenosis of RV outflow tract or pulmonary artery on cine-MR or MR angiogram images is detected .
Furthermore, in patients with corrected ToF, dys-synchrony of RV contraction or abnormal excursion of interventricular septum, easily recognised on cine MR images, contribute to RV dysfunction and are often associated with fibrosis at the interventricular junction points, suggesting a mechanism of adverse interventricular interaction (Fig. 2) [14, 15].
Transposition of great arteries
In patients with congenitally corrected transposition or transposition that has been corrected with atrial switch, the morphological RV pumps blood to the aorta.
For these patients, the accurate measurement of ventricular volumes obtained by CMR is useful in assessing adaptive modification to systemic resistance leading to RV dilation and hypertrophy [10, 11].
In patients treated with arterial switch, the RV may appear normal due to the corrected atrio-ventricular-arterial discordance; however, CMR is performed not only to evaluate bi-ventricular function and morphology but also to rule out potential complications in the vessels, patches or valves [10, 11].
Ebstein’s anomaly is a rare malformation of the tricuspid valve, characterised by the dilatation and apical displacement of the insertion of the septal leaflet and a redundant, elongated anterior leaflet (Fig. 4).
By definition, a part of the RV is anatomically ventricular but functionally atrial (“atrialised”) and entirely contains the tricuspid valve. The remaining functional RV is small.
CMR, using stacks of cine sequences acquired on short-axis, four-chamber and a RV vertical long-axis (RV inflow-outflow plane), allows measurement of the size and systolic function of the right chambers even in cases of severe disease with marked distortion of the RV anatomy .
The right atrium and atrialised RV are remarkably enlarged when the sum of the right atrium and atrialised RV area is larger than the combined area of the functional RV, left atrium and left ventricle, measured on four-chamber view at the end diastole .
Moreover, the severity of tricuspid regurgitation can be estimated using a through-plane velocity-encoded sequence, oriented perpendicular to the regurgitant jet immediately on the atrial side.
A jet cross-sectional area equal or greater than 6 × 6 mm, setting 250 cm/s as encoding velocity, can be regarded as severe .
An atrial septal defect occurs in about 50 % of adult Ebstein patients and should be ruled out on atrial short-axis cine images .
Ischaemic cardiac disease
Involvement of the RV occurs in approximately 50 % of patients with inferior myocardial infarction (MI), whereas signs of RV ischaemia have been reported with CMR in around 33 % of anterior LV MI [4, 19, 20, 21]. Increasing interest in non-invasive recognition of RV MI is justified by its prognostic and therapeutic implications (adverse RV remodelling and worsening of functional recovery at follow-up). These patients have higher rates of in-hospital morbidity and mortality than isolated LV infarction, thus requiring more aggressive treatment approaches [3, 19, 20]. A significant discrepancy, however, between the frequency of RV MI at autopsy and detected cases amongst living patients demonstrates an underestimation of the phenomenon by routine clinical and instrumental criteria (electrocardiography, echocardiography, haemodynamic monitoring).
CMR represents an ideal tool for its detection in both acute and chronic MIs although the thinned infarcted wall of the RV (mostly in chronic lesions) is not always easily detected with either T2WI and LGE-T1WI sequences .
MR features of right ventricular myocardial infarction
Right ventricular dilatation, abnormal right ventricular wall motion, paradoxical motion of septum and tricuspid regurgitation are typical CMR features of RV MI, although RV transient dysfunction is frequently caused by a post-infarct stunning of RV myocardium in a LV MI .
A combined T2-weighted imaging/LGE imaging CMR approach enables the characterisation of reversibly and irreversibly damaged myocardium, and monitoring the progression from acute to chronic RV infarction (Fig. 5) .
Arrhythmogenic right ventricular cardiomyopathy/dysplasia
Arrhythmogenic right ventricular cardiomyopathy (ARVC) is an inherited cardiomyopathy, predisposing patients to ventricular arrhythmias and sudden cardiac death. It is characterised by structural and functional abnormalities of the right ventricular myocardium, such as fibrofatty myocardium replacement, microaneurisms or focal atrophy .
Diagnosing ARVC is currently challenging due to the lack of an established and definite “gold standard” test, even including endomyocardial biopsy.
Although the revised criteria proposed by the Task Force of the European Society of Cardiology and the Scientific Council on Cardiomyopathies of the International Society and Federation of Cardiology in 2010  confirmed the crucial role of CMR in diagnosing ARVC, a vigorous debate on the appropriate indications to CMR in patients with suspected ARVC is still ongoing.
MR features of arrhythmogenic right ventricular cardiomyopathy/dysplasia
Recognition of fibrofatty myocardium replacement on CMR images is not a specific feature for ARVC, as it is frequently observed in elderly patients as part of the ageing process or as result of healed MI .
Moreover, differentiating myocardial from epicardial fat is often problematic due to the limited intrinsic spatial and contrast resolution of CMR. Notably, in ARVC, fat infiltration has been described to extend from the epicardium towards the endocardium; hence the RV free wall is remarkably thin. In healed MI, conversely, fat is band-like and mainly located in the subendocardial or mid-wall myocardium. On the other hand, RV free wall maintains normal or increase thickness in healthy patients with physiological fat .
In order to distinguish between LGE and fat, and to differentiate pathological fatty infiltration from the epicardial fat, TSE sequences (“black blood”) should be acquired with and without fat saturation covering the entire volume of RV (Table 2).
The use of gadolinium in cases of suspected ARVC may be justified by the possible evidence of late enhancement related to fibrous degeneration in RV myocardium, with special focus to the so-called “triangle of dysplasia” (including diaphragmatic, apical and infundibular regions) .
Hypertrophic cardiomyopathy (HCM) is the most common hereditary heart disease that usually affects the LV and can cause sudden cardiac death and heart failure at any age.
Notwithstanding the fact that the RV has long been considered spared by HCM, the introduction of CMR has revealed an incidence of RV involvement at around 33 % (if considered RV wall thickness > 8 mm) among HCM patients population . It may result in a RV outflow obstruction and/or an impaired RV diastolic filling with potentially severe dyspnea, supraventricular arrythmias and pulmonary thromboembolism.
Occasionally, myocardial disarray of the right ventricular myocardium can be revealed on LGE imaging and can indicate a potential arrhythmogenic substrate and its extent reflects the severity of the disease .
In the quantitative assessment of RV function, ejection fraction is usually similar to normal subjects, whereas end-diastolic volume is slightly lower due to diastolic filling dysfunction (likewise to functional changes observed in hypertrophied LV); this observation may suggest a unique primary hypertrophic process developing similarly in both ventricles 
Non-compaction cardiomyopathy (NCCMP) is characterised by a spongy appearance of the ventricular myocardium due to multiple, prominent trabeculations and deep intertrabecular recesses in communication with the ventricular cavity.
Typically, non-compaction involves the apical portion of the LV and predisposes to thromboemboli, arrhythmias, sudden death, ventricular dysfunction and heart failure.
CMR identifies left ventricular NCCMP with a sensitivity of 86 % and a specificity of 99 % using a cut-off ratio of non-compacted/compacted myocardium >2.3, measured on cine images at end-diastole .
However, RV non-compaction has been rarely described , since shared criteria to distinguish between normal RV trabeculations and non-compacted pattern has not yet been codified, thus making findings easily undiagnosed by inexperienced readers.
Left ventricular LGE was depicted in patients with NCCMP according to the presence of fibrosis, and recently demonstrated to be correlated to clinical severity and ventricular dysfunction .
CMR provides unique diagnostic clues to rule out this uncommon clinical entity due to its superior morphological depiction, which allows to objectively and reproducibly identify the extent of pathological hypertrabeculations, to depict eventually associated regional kinetic abnormalities and to exclude endocavitary thrombi.
Cor pulmonale is defined as dilation and hypertrophy of the RV as a response to elevated pulmonary arterial pressure (pulmonary hypertension [PH]).
Typical CMR features of PH are RV dilation with unusual hypertrophy, right atrium dilation, flattened or reversed septum curvature (bulging) with dyskinetic movement . LGE imaging shows a characteristic retention of gadolinium at the septal insertion (junctional pattern), predicting RV remodelling in response to increased afterload .
Initial and predictive signs of PH at CMR are considered to be a slowed and turbulent flow-pattern of the pulmonary artery. It has recently been utilised in the measurement of the degree of whirling flow on phase-contrast imaging and the distensibility of the pulmonary trunk on the cine CMR images by comparing systolic and diastolic transverse diameters [33, 34].
Other non-ischaemic cardiomyopathies
In the most of these conditions, however, the CMR features resemble the LV pattern, as observed in several case reports.
Right ventricular masses
The masses most frequently encountered in the RV are non-tumoral, such as thrombi, valvular vegetations, focal muscular hypertrophy and pericardial cysts but despite their non-neoplastic nature they may lead to severe complications (embolisation, ventricular function impairment) .
Finally, it has estimated that secondary cardiac tumours are a hundred times more common compared with primary lesions ; and the RV may be reached by direct extension such as (e.g. lung or breast cancer), lymphatic extension (e.g. lymphoma), or metastatic spread (e.g. malignant melanoma or renal cell carcinoma) .
CMR allows a comprehensive evaluation of the right ventricle both in terms of anatomical delineation, function quantification and tissue characterisation.
A proper knowledge of the most common CMR features of RV diseases is necessary in order to promptly and accurately identify the RV involvement in various cardiac diseases.
No grants have been received regarding this work.
The authors have no conflicts of interest to declare and have no direct or indirect financial interest in the subject matter of this manuscript.
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