Role of Myocardial Collagen in Severe Aortic Stenosis With Preserved Ejection Fraction and Symptoms of Heart Failure.

INTRODUCTION AND OBJECTIVES: We investigated the anatomical localization, biomechanical properties, and molecular phenotype of myocardial collagen tissue in 40 patients with severe aortic stenosis with preserved ejection fraction and symptoms of heart failure.

METHODS: Two transmural biopsies were taken from the left ventricular free wall. Mysial and nonmysial regions of the collagen network were analyzed. Myocardial collagen volume fraction (CVF) was measured by picrosirius red staining. Young's elastic modulus (YEM) was measured by atomic force microscopy in decellularized slices to assess stiffness. Collagen types I and III were measured as CI VF and CIII VF, respectively, by confocal microscopy in areas with YEM evaluation.

RESULTS: Compared with controls, patients exhibited increased mysial and nonmysial CVF and nonmysial:mysial CVF ratio (P < .05). In patients, nonmysial CVF (r = 0.330; P = .046) and the nonmysial:mysial CVF ratio (r = 0.419; P = .012) were directly correlated with the ratio of maximal early transmitral flow velocity in diastole to early mitral annulus velocity in diastole. Both the CI VF:CIII VF ratio and YEM were increased (P ≤ .001) in nonmysial regions compared with mysial regions in patients, with a direct correlation (r = 0.895; P < .001) between them.

CONCLUSIONS: These findings suggest that, in patients with severe aortic stenosis with preserved ejection fraction and symptoms of heart failure, diastolic dysfunction is associated with increased nonmysial deposition of collagen, predominantly type I, resulting in increased extracellular matrix stiffness. Therefore, the characteristics of collagen tissue may contribute to diastolic dysfunction in these patients.