Is myocardial fibrosis appropriately assessed by 2D strain derived integrated backscatter?

Abstract Introduction Calibrated integrated backscatter (cIB) may be obtained from bidimensional (2D) strain echocardiography as a quantification measurement of myocardial ultrasound reflectivity. Increased collagen content of the myocardium modifies tissue reflectivity and cIB is suggested as a marker of left ventricular (LV) fibrosis. However, its diagnostic accuracy is not fully established. Aim To assess the correlation between cIB by 2D strain and LV myocardial fibrosis (MF), as evaluated by non-invasive imaging and histopathology. Methods Correlation study from a cohort of 157 patients with severe symptomatic aortic stenosis (AS) referred for surgical aortic valve replacement (AVR). Patients with complete preoperative transthoracic echocardiography, cardiac magnetic resonance (CMR) and endomyocardial biopsy (EMB) obtained from the anterior basal septum at the time of AVR were selected. Two groups of 30 patients were evaluated, with and without late gadolinium enhancement (LGE) at CMR. Integrated Backscatter was obtained at QRS peak in decibels (dB) from both parasternal long axis (PLAX) and apical-three-chamber (A3C) cine clips at Qanalysis. cIB was calculated by subtracting the pericardial intensity from the average of the anteroseptal and basal inferolateral wall values. Correlation analysis was performed for the whole group of patients with global and segmental (anterior basal septum) values of native T1 and extracellular volume (ECV), and EMB collagen volume fraction (CVF) from Masson´s Trichrome staining. IBS values were compared in both group of patients. Results 60 patients (74 [36-74] years, 45% male) with high gradient (mean gradient: 63±20mmHg), normal flow (45±10mL/m2), preserved ejection fraction (60±9%) AS were included. Basal septal cIB was –9.17±9.45dB and –17.45 (–31.2–10.95) dB from A3C and PLAX views, respectively. These indexes did not correlate with basal septum thickness or global LV mass. Absolute and cIB did not correlate neither with global and regional T1 and ECV values, nor with CVF at EMB. These were not significantly different in both groups of patients and there was no correlation between cIB values and mass of replacement MF in patients with LGE. Conclusion In these cohort of patients with classical severe AS, there was no correlation of cIB with imaging markers of both replacement and diffuse MF. cIB also didn´t correlate with CVF at histopathology. These findings suggest that reflectivity indexes are not suitable for myocardial tissue characterization in this setting.