Abstract 4367959: Integrated Evaluation of Diastolic Function and Myocardial Tissue Characteristics in Non-Dilated Cardiomyopathy

Background: A subset of patients with non-dilated left ventricular cardiomyopathy (ND-LVCM) presents with restrictive-like physiology despite preserved left ventricular size. However, the pathological and imaging correlates of this diastolic dysfunction remain insufficiently characterized. Hypothesis: We hypothesized that diastolic dysfunction in ND-LVCM is associated with myocardial fibrosis or infiltration and corresponds with specific echocardiographic and MRI findings. Methods: We retrospectively analyzed 169 patients with ND-LVCM (LV end-diastolic diameter <55 mm) who underwent endomyocardial biopsy, cardiac MRI, and echocardiography including global longitudinal strain (GLS). Fibrosis was quantified using Masson's trichrome staining and categorized into interstitial, subendocardial, or perivascular patterns. In cardiac amyloidosis, Congo red–positive deposition was semi-quantified as diffuse, scattered, or perivascular. Restrictive-like physiology was defined by LA diameter >40 mm, E/e′ >15, elevated BNP, and LVEF ≥50%. Results: Diagnoses included cardiac amyloidosis (n=56), sarcoidosis (n=14), Fabry disease (n=12), hypertensive cardiomyopathy (n=49), and hypertrophic cardiomyopathy (n=38). Approximately 40% of patients exhibited restrictive-like physiology. These patients demonstrated significantly greater fibrosis burden (median 10.1% vs. 5.6%, p<0.001), higher prevalence of interstitial and perivascular fibrosis, and more frequent mid-wall or subepicardial late gadolinium enhancement (LGE) on MRI. Echocardiography showed reduced GLS and shortened deceleration time in these cases. In amyloidosis, diffuse deposition was particularly associated with more pronounced impairment in diastolic markers. Fabry disease was characterized by impaired relaxation without overt restrictive features, while sarcoidosis presented with heterogeneous diastolic profiles. Conclusions: Restrictive diastolic physiology in ND-LVCM spans multiple etiologies and correlates with distinct histologic and imaging features. An integrated approach combining echocardiography, MRI, and myocardial biopsy offers valuable insights into disease mechanisms and may aid in the differentiation of restrictive cardiomyopathy phenotypes.