Imaging of right ventricular morphofunctional abnormalities

Demonstration of right ventricular morphofunctional abnormalities by echocardiography, angiography, and MRI is a major criterion for diagnosing ARVC.5 Functional and structural abnormalities consist of global right ventricular dilatation with or without ejection fraction reduction and left ventricular involvement; segmental right ventricular dilatation with or without dyskinesia (aneurysms and bulgings); and wall motion abnormalities such as ipo-akinesia or dyskinesia.

All the imaging techniques are associated with significant limitations in the diagnostic accuracy for detecting right ventricular changes. Right ventricular angiography is usually regarded as the gold standard for the diagnosis of ARVC. Angiographic evidence of akinetic or dyskinetic bulgings localised in infundibular, apical, and subtricuspidal regions has a high diagnostic specificity (over 90%).u Large areas of dilatation akinesia with an irregular and "mamillated" aspect, most often involving the inferior right ventricular wall, are also significantly associated with the diagnosis of ARVC. However, considerable interobserver variability regarding the visual assessment of right ventricular wall motion abnormalities by contrast angiography have been reported.

Compared with right ventricular angio-graphy, echocardiography is a non-invasive and widely used technique, and represents the first line imaging approach in evaluating patients with suspected ARVC or in screening family members. Echocardiography also allows serial examinations aimed to assess the disease progression during the follow up of affected patients. Furthermore, echocardiography is a reliable technique for differential diagnosis of ARVC by easily ruling out other right ventricu lar diseases such as Ebstein anomaly, atrial septal defect, etc. Other than a visual assessment of wall motion and structural abnormalities, a quantitative echocardiographic evaluation of the right ventricle, including measurements of end diastolic cavity dimensions (inlet, outlet, and mean ventricular body), wall thickness, volume, and function, is mandatory in order to enhance the diagnostic accuracy. In the presence of the typical echocardiographic features, contrast angio-graphy or MRI may be avoided, whereas borderline or apparently normal findings in patients with suspected disease requires further examination.

MRI is an attractive imaging method because it is non-invasive and has the unique ability to characterise tissue, specifically by differentiating fat from muscle.12 Recent studies have shown several limitations and a high degree of interobserver variability in the MRI assessment of free wall thinning and fatty deposition that are the most characteristic structural changes (fig 14.3). The right ventricular free wall is only 4-5 mm thick and the motion artifacts often result in insufficient quality/spectral resolution to quantify right ventricular wall thickness accurately. The normal presence of epicardial and pericardial fat also makes identification of true intramyo-cardial fat difficult. Some areas—such as the subtricuspidal region—are not easily distinguished from the atrioventricular sulcus which is rich in fat. There has been recent emphasis on functional methods such as right ventricular volume estimation with cine MRI. This approach also permits accurate assessment of right ventricular wall motion abnormalities and focal areas of dilatation with or without dyskinesia. In conclusion, although MRI is a promising technique for delineating right ventricular anatomy and function, as well as for characterising the composition of the right ventricular wall, its diagnostic sensitivity and specificity still need to be defined since the quality of images detected are, at the present time, largely subject to individual interpretation.

Radionuclide angiography is also an accurate non-invasive imaging technique for detection of global right ventricular dysfunction and regional wall motion abnormalities; its diagnostic concordance with right ventricular angiography is nearly 90%.

The diagnosis of ARVC at its early stages or in its concealed variants remains a clinical challenge by all imaging methods. Although these techniques appear to be accurate in detecting right ventricular structural and functional abnormalities in overt forms of ARVC, they are less sensitive in detecting subtle lesions.

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