Complete atrioventricular block revealing late-onset cardiac Fabry disease: diagnostic role of native T1 mapping

A 63-year-old man presented with symptomatic complete atrioventricular block requiring urgent pacemaker implantation. Evaluation revealed non-obstructive left ventricular hypertrophy with normal coronary arteries. Cardiac magnetic resonance showed diffusely reduced native T1 values and inferolateral late gadolinium enhancement, suggesting Fabry cardiomyopathy; amyloidosis was excluded by bone scintigraphy. Diagnosis was confirmed by markedly reduced alpha-galactosidase A activity, elevated lyso-Gb3, and a pathogenic hemizygous GLA variant (p.Asn215Ser). Enzyme replacement therapy with agalsidase beta was initiated, with early stabilization of myocardial deformation and septal thickness. This case highlights native T1 mapping as a key diagnostic biomarker in unexplained left ventricular hypertrophy.