Decoding hypertrophic cardiomyopathy mimics: key strategies in the differential diagnosis of septal bulge

Abstract Background and Introduction Current classification for cardiomyopathies rely predominantly on imaging phenotypes. However, diagnostic criteria remain poorly defined for hypertrophic cardiomyopathy (HCM) phenocopies when no clear underlying pathological basis is evident. This diagnostic uncertainty may lead to misinterpretation of structural cardiac variant, particularly in cases of ventricular septal bulge (VSB). Study Objectives This study aimed to systematically characterise and differentiate the clinical presentation, electrocardiographic features, and advanced imaging characteristics of VSB mimicking HCM, to establish robust diagnostic criteria for this phenocopy. Methods From 1,425 consecutive patients referred for cardiovascular magnetic resonance (CMR) at our tertiary centre, we identified 76 patients with echocardiographic findings suggestive of HCM but ultimately diagnosed with isolated VSB. Exclusion criteria included any clinical or imaging evidence of secondary causes for ventricular hypertrophy. A control group of patients with definitive diagnosis of HCM was included for comparative analysis. (N=24) Results Key findings demonstrated: Morphological characteristics: -VSB patients maintained normal left ventricular wall thickness though all exhibited a prominent septal bulge, with a significant mean difference of 2 mm compared to HCM (p