Assessment of Myocardial Fibrosis Using Multimodality Imaging in Severe Aortic Stenosis: Comparison With Histologic Fibrosis

Objectives: This study assessed diffuse myocardial fibrosis (MF) by cardiac magnetic resonance (CMR) imaging and speckle-tracking echocardiography (STE) in patients with severe aortic stenosis (AS) and validated findings by using histologic confirmation of MF. Background: MF is a concomitant pathologic finding related to hypertrophic response in severe AS. It would be beneficial to have reliable imaging methods to assess MF. Methods: CMR and STE were performed in 71 consecutive patients with severe AS before aortic valve replacement. The extracellular volume (ECV) and native T1 values obtained by CMR and global longitudinal strain (GLS) values by STE were measured. The degree of MF was quantified by using Masson trichrome stain in myocardial biopsy specimens obtained intraoperatively. The study population was divided into 3 groups according to the degree of MF on histology (mild, moderate, and severe MF). Results: The severe MF group had a higher incidence of heart failure (HF) and diastolic dysfunction than the mild and moderate MF groups. The ECV (r = 0.465; p < 0.0001), GLS (r = 0.421; p = 0.0003), and native T1 (r = 0.429; p = 0.0002) values were significantly correlated with the degree of MF. GLS was moderately correlated with ECV (r = 0.455; p = 0.0001) and less with the native T1 (r = 0.372; p = 0.0014) value. The model using ECV (R ^{2 =} 0.44; Akaike Information Criterion [AIC] = 55.8) was found to predict the degree of MF most accurately than that with GLS (R ² = 0.35; AIC = 66.84) and the native T1 (R ² = 0.36; AIC = 66.18) value. The secondary endpoint of interest was clinical outcome of a composite of total mortality, admission for HF, or development of HF symptoms. During follow-up (median: 4.6 years), and there were 16 clinical events. Although statistically insignificant, ECV is more closely related to prediction of the clinical outcome than native T1 or GLS. Conclusions: ECV as assessed by CMR could be an ideal surrogate marker for diffuse MF in patients with severe AS among all 3 models considered.