CMR in diagnosis of Arrhythmogenic cardiomyopathy
As the diagnostic criteria evolved and studies over the decades have uncovered more about the various phenotypic expression of ARVC, CMR imaging has emerged as the noninvasive gold standard for ARVC workup. It provides a useful tool to evaluate morphology, function, and tissue characteristics. It can highlight myocardial fibrosis, fatty replacement or identify wall motion abnormalities with high accuracy. The most recent 2020 International diagnostic criteria of arrhythmogenic cardiomyopathy relies on CMR to characterize the phenotype and aid with the exclusion of other diagnoses. The new criterion adds the minor criterion for the diagnosis of biventricular or left dominant variants with the demonstration of LV systolic dysfunction.18,19
Late gadolinium enhancement (LGE) of the myocardium is often used to assess myocardial fibrosis but has a limited role in the current diagnostic criteria of ARVC. LGE is nonspecific and the differential diagnosis can include sarcoidosis, myocarditis, amyloidosis, or dilated cardiomyopathy.20 Furthermore, LGE is less useful in classic ARVC where the thin RV wall makes the technique less useful, in comparison to LDAC where LGE has been reported in up to 61% of cases presenting in a circumferential, mid-myocardial pattern extending to the right side of the septum.21 Of note the circumferential or mid-myocardial fibrosis pattern is seen in only left dominant/biventricular ARVC. Autopsy studies of ARVC patients have demonstrated fibro-fatty infiltration predominantly on the epicardial surface leading to the understanding that the disease starts in the epicardium with progression toward the endocardium. LV systolic dysfunction can become more severe in advanced stages as there is progression of transmural involvement. Our patient’s second CMR study reflected early yet significant changes with normal cavitary size/wall thickness but mild-moderate hypokinesis of the mid to apical lateral wall. Furthermore, he had predominately epicardial fibrosis in a relatively circumferential pattern of the lateral wall with mid myocardial fibrosis involving the septal walls.