Ultrastructural myocardial changes in patients with severe aortic stenosis referred for surgical aortic valve replacement
Authors: Abecasis J , Maltes S , Lopes P , Reis Santos R , Ferreira A , Neves J P , Sousa Uva M , Gil V , Ramos S , Felix A , Cardim N 
Published: November 2023

Abstract

Structural myocardial adaptation to pressure overload such as severe aortic stenosis (AS) goes further beyond cardiomyocyte hypertrophy. Progressive fibrosis takes part in left ventricular (LV) remodeling and drives the transition to heart failure. However, the mechanisms underlying this are not fully clarified.

Aim
To assess ultrastructural myocardial changes occurring in patients with severe AS referred for surgical aortic valve replacement (SAVR).

Methods
Prospective study of 158 patients (70.9±7.8y, 50%women), with severe symptomatic AS (mean gradient: 60.9±17.4mmHg; valve area: 0.72±0.17cm2; all with high gradient) referred for SAVR with no history of ischemic cardiomyopathy. All patients had complete pre-operative transthoracic echo (LV ejection fraction: 58.9±9.2%; GLS:-14.9±3.7%) and cardiac magnetic resonance with tissue characterization: LV mass index: 80.1±5.9g/m2. Myocardial samples were obtained in 99 patients (62.3%) from intraoperative septal biopsy. Tissue was stained with Verhoeff and Masson´s trichrome for elastic fibers and myocardial fibrosis (MF) assessment, respectively. MF was quantified at an automatic algorithm (QuPath). Inflammation was searched through CD45, CD3, CD20 and CD68 immunostaining. Extracellular matrix (ECM) characterization was performed in 34 samples (alpha-actin, type I collagen, fibronectin and tenascin C immunostaining).

Results
Mid-wall late gadolinium enhancement was present in 103 patients (65,1%) with a median fraction of 1.9%[IQR 0,1-6,0%] of LV mass. Global LV native T1 and T2 values and extracellular volume fraction were within normal ranges (1057.8±75.4ms, 39.9±4.3ms, 24.7±6.2%, respectively). At histopathology (sample size: 2,446mm [IQR 1,790-3,350mm]) there was cardiomyocyte hypertrophy (median diameter 35mm[IQR 30.2-42.0mm])(Fig, A), variable elastic deposition (elastic endocardium ratio 0.40[IQR 0.2-0.5])(Fig, B), predominant perivascular fibrosis (93.9%) (Fig, C), with a median MF of 13.3% [IQR 7.1-21.0%];57.6% of the patients with dysplastic vessels (Fig, C). Cardiomyocyte enlargement, cytoplasmatic vacuolization and myofiber detachment occurred in 40 cases (40.4%) (Fig, D). This was confirmed as stunning at Periodic acid-Schiff-diastase stain. Inflammation was considered absent in all cases as inflammatory cells were scantily present (median number of CD45+ cells/field: 3[IQR 1.35-6.0]; predominant CD3+). Type I collagen matched MF distribution, following vessel web, such as fibronectin (Fig, E-H). Alpha-actin was detected at the subendocardium in 2/3 of the cases; tenascin C was diffusely positive in 9 cases (27%)(Fig, I).

Conclusion
These patients with classical severe symptomatic AS were referred for SAVR with diverse ultrastructural myocardial changes. Myocardial stunning occurs in a significant proportion of patients despite the absence of ischemic cardiomyopathy. Inflammation is not involved at this stage of the disease. Distinct grades of ECM remodeling are probably occurring.Figure