Cardiac MRI identifies interatrial septum late enhancement as a hallmark of amyloidosis

BACKGROUND: Cardiac amyloidosis (CA) is an infiltrative cardiomyopathy with high morbidity and mortality, often presenting with non-specific clinical and imaging features. Cardiac magnetic resonance (CMR) enables tissue characterization but lacks specificity in differentiating CA from phenocopies remains limited. OBJECTIVE: This study aimed to evaluate interatrial septum (IAS) and atrial walls late gadolinium enhancement (LGE) patterns to improve the differentiation of CA from other cardiomyopathies. METHODS: A retrospective analysis was conducted including 159 patients: 55 with CA, 52 with hypertrophic cardiomyopathy (HCM), and 52 with dilated cardiomyopathy (DCM). IAS thickness, atrial morphology and LGE patterns were assessed using CMR. Anterior and posterior IAS were defined relative to the fossa ovalis in 4-chamber cine views. RESULTS: IAS thickness did not differ significantly between groups. IAS LGE was significantly more frequent in CA compared with HCM and DCM (anterior IAS: 83.3 % vs 15.4 % vs 26.9 %; posterior IAS: 86.8 % vs 42.3 % vs 65.4 %; p < 0.001 for all comparisons). Atrial LGE was also more prevalent in CA (74.1 % vs. 30.8 % in HCM and 32.7 % in DCM; p < 0.001 for all comparisons). Intense IAS LGE-defined as enhancement equal to or greater than ventricular LGE- demonstrated high specificity (98 %) for CA. CONCLUSION: Intense anterior IAS LGE - with a specificity of 98 % - represents the most diagnostically relevant CMR feature for CA in this cohort. Its systematic assessment during routine CMR may improve diagnostic discrimination between CA and cardiomyopathy phenocopies.