Left Ventricular Isoperimetric Properties in Hypertrophic Cardiomyopathy: A CMR-Based Analysis of Ventricular Geometry.

Background/Objectives: Hypertrophic cardiomyopathy (HCM) is a complex myocardial disease in which structural remodeling extends beyond conventional parameters such as maximal wall thickness (MWT). This study aimed to evaluate isoperimetric analysis as a geometry-based approach for characterizing left ventricular (LV) morphology and to compare its performance with fractal analysis in distinguishing HCM from non-HCM subjects. Methods: This retrospective study included 120 subjects (60 HCM and 60 controls) who underwent clinically indicated CMR. Endocardial contours were delineated on short-axis cine images at end-diastole. The isoperimetric index (IPI), cavity-corrected IPI (CC-IPI), and fractal dimension (FD) were calculated. Group comparisons, correlations, and receiver operating characteristic analyses were performed. Results: Patients with HCM showed significantly higher IPI and CC-IPI values than controls (p < 0.001), including in sex-stratified analyses. IPI and CC-IPI correlated strongly with MWT (r = 0.867) and LV mass index (r = 0.807 and 0.803, respectively), moderately with native T1 (r = 0.567), and weakly with end-diastolic volume index (r = 0.256 and 0.253, respectively) and stroke volume (r = 0.237 and 0.229, respectively). No association was observed with late gadolinium enhancement. IPI and CC-IPI showed a strong linear correlation (R2 = 0.997), with both indices demonstrating high discriminatory performance (AUC = 1.00). Conclusions: HCM is associated with notable alterations in LV endocardial geometry beyond myocardial hypertrophy alone. IPI and CC-IPI provide simple, size-normalized, and physiologically interpretable morphologic descriptors that complement conventional CMR parameters and FD-based contour complexity analysis.