Cardiac MRI in various right heart pathologies: Case based discussion

Introduction

With increasing incidence of heart diseases, there is a need for early detection and accurate diagnosis.Recent advances in cardiac imaging, has tremendously affected patient management. Cardiovascular MRI is an important imaging tool which has changed the scenario of current clinical practice.

Cardiovascular MRI offers valuable information aboutvarious conditions. They include,

• Ischaemic heart disease (Viability study, adenosine stress perfusion CMR)
• Non-ischaemic cardiomyopathy, Hypertrophic cardiomyopathy, arrhythmogenic right ventricular dysplasia/cardiomyopathy.
• Myocarditis.
• Congenital heart disease.
• Pericardial disease and cardiac tumours.

Left ventricle is primarily involved in ischaemia and other pathologies. Hence right heart is often considered as ‘forgotten chamber’.The purpose of this article is to illustrate few common right heart pathologies with description of clinical picture and imaging findings.

Echocardiography evaluation has limited role due to its thin wall,peculiar morphology and anterior position in the chest.1 In this background CMR has emerged as a preeminent modality to evaluate various right heart diseases. It has unique capability in providing accurate and reproducible assessment of function and tissue characterization. This helps in the treatment planning in various congenital heart diseases.²

The present review illustrates basic anatomy and CMR features of various right heart pathologies.

Anatomy

The right atrium which receives deoxygenated blood from superior and inferior vena cavae is located antero-laterally inferior to the left atrium. The inferior vena cava (IVC) enters the right atrium near the septumwhile superior vena cava (SVC) enters from the roof of the right atrium. On the anterior left margin, the coronary venous return occurring towards the right atrium is seen through the coronary sinus.³

A smooth linear crista terminalis appearing isointense to myocardium can be seen running from the opening of SVC towards the opening of IVC within the right atrium. A flat triangular right atrial appendage with trabeculations can be seen.

The right ventricle is seen looping around the left ventricle. It has thinner and more trabeculated wall. The moderator band running from the cardiac septum towards the lateral wall is helpful in identification.

The tricuspid valve has three leaflets and can be readily evaluated in terms of cross sectional area and flow across it. The valves of coronary sinus –Thebesian valve and of inferior vena cava- The Eustachian valve can also be seen well on CMR (Fig 1 and 2).

Case 1:

A 23 year old male presented with bouts of palpitation, ECG showed ventricular arrhythmias with left bundle branch block.

Cardiac MRI shows corrugated/crenated RV myocardium with dyskinesia and small microaneurysms. The right ventrcular function is also impaired due to dys-synchronous RV contraction.4These features are suggestive of arrhythmogenic right ventricular dysplasia. Recognition of fibro-fatty myocardial replacement is no longer considered as a specific feature. Instead Modified task force criteria⁵ stresses the following features (Fig.3).

-Regional RV akinesia/dyskinesia.

-RV ejection fraction <40%

-RV end diastolic volume (Indexed values >110 ml in males and >100 in females.)

Case 2:

A 35 year old female presented with breathlessness. ECG was essentially normal. Echocardiography was suggestive of pulmonary artery hypertension.

MRI revealed considerable enlargement of right atrium and ventricle, with increased trabeculations.

Imaging features were suggestive of Cor Pulmonale.

Cor pulmonale is defined as dilatation and hypertrophy of right ventricle as a response to elevated pulmonary arterial pressure.6 Large spectrum of diseases such as heritable disorders, pulmonary thromboembolic lung diseases and idiopathic pulmonary arterial hypertension causefollowing features:

Right ventricular dilatation with hypertrophy. Right atrial dilatation.

Flattened or reversed septum curvature with dyskinetic movements.

Case 3:

A  25 year old male was evaluated in view of abnormal chest discomfort.

CMR Findings: Q flow images on CMR revealed significant alteration of pulmonary to systemic flow ratio (QP/QS>1.5). This is suggestive of hemodynamically significant right-to-left shunt. Findings also revealed small atrial septal defect with right superior pulmonary vein communicating with superior vena cava / Right atrium.

These features are suggestive of sinus venousus atrial septal defect with partial anomalous venous drainage of right superior pulmonary vein into superior vena cava⁷.

Associated congenital cystic adenomatoid malformation, heterotaxy, congenital diaphragmatic hernia and asplenia are to be looked for on CMR (Fig.5).

Case 4:

A 55 year old male patient was evaluated in view of the complaints of fatigue and shortness of breath. Echocardiography showed right atrial enlargement and significant tricuspid regurgitation.

CMR Spin echo sequences clearly showed apical displacement of septal and posterior leaflets of the tricuspid valve. The tricuspid valve septal attachment was 3.2 cm(more than 1.5cm) beneath the mitral valve septal attachment. On comparison with the mitral valve, the septal displacement was more than 8mm/ m2– beyond the cut off value. This led to atrialisation of the right ventricle, which was evident on coronal images .There was associated tricuspid regurgitation which was seen on cine and velocity encoded images.These features were suggestive of Ebstein’s anomaly⁸.

Main diagnostic features are

-Massive enlargement of right atrium.

- Tricuspid regurgitation.

-Marked distortion of RV anatomy with atrialisation.

-Considerable RV dysfunction.

-Atrial septal defect occurs in about 50%of adult Ebstein patients.

Case 5:

A 56 year old male on chemotherapy with indwelling catheter presented with shortness of breath. Echocardiography was non-conclusive as all four chambers could not be well visualized.

CMR Features revealed a well-defined homogenously hypointense non-mobile intracavitary lesion was seen in right atrium. No obvious stalk was visualized. No abnormal enhancement was noted on delayed images. The lesion was persistently hypointense. No foci of blooming were seen on Gradient images. These features were suggestive of right atrial thrombus.

Right atrial thrombus can be classified as follows.

Type A – Morphologically serpiginous, highly mobile thrombus- often associated with deep vein thrombosis (DVT) – these are often emboli that get caught in transit.

Type B –Non mobile thrombus formed in situ commonly associated with primary cardiac pathology.

Type C – These are rare thrombi-similar to myxoma-usually mobile.

Conclusion

Cardiac MRI with its multiplanar capability provides accurate evaluation of various right heart diseases. It offers great advantage of accurate function measurements, which can provide insight into the patho=physiology of disease. Detailed morphology has increased diagnostic sensitivity and accuracy of diseases such as arrhythmogenic cardiomyopathy. Thus CMR truly behaves like kaleidoscope in imaging of right heart diseases.