Size of myocardial fibrosis by LGE, pre- and post-contrast T1 and ECV in patients with hypertrophic cardiomyopathy referenced to normal appearing myocardium or healthy volunteers

Abstract

Background: Myocardial fibrosis is associated with abnormal cardiac remodeling and poor prognosis in patients with hypertrophic cardiomyopathy. Currently, new cardiac MRI (CMR) techniques such as T1- mapping and extracellular volume (ECV) measurement are available to quantify diffuse myocardial fibrosis. We analyzed the size of myocardial fibrosis using pre- and post-contrast T1, ECV and late gadolinium enhancement (LGE) in patients with HCM referenced to normal appearing myocardium and referenced to normal values of healthy volunteers. Methods: CMR was performed in 21 patients with HCM (56±4.6 years,10 women) using a 1.5T scanner (Achieva, Philips). Myocardial lesions were assessed on 3 representative short axes of the apex, center and basis of the left ventricle by phase-sensitive inversion-recovery (PSIR) LGE-images, pre- and post-contrast T1 maps and ECV maps. Size of fibrosis was quantified in percent of left ventricular (LV) myocardium by a threshold method relative to normal appearing myocardium using a cutoff >2 SD above normal appearing remote myocardium on all images and relative to normal values assessed from 20 healthy volunteers on T1 and ECV maps. Post-contrast images were obtained after injection of 0.075 mmol/ kg Gd-BOPTA. Data were analyzed using the HeAT software. Results: Size of fibrosis relative to remote normal appearing myocardium was 20±15%LV on LGE images and 17±16%LV on ECV maps (p=0.49). Smaller fibrosis sizes were found on native T1 maps with 14±12%LV (p=0.017) and on post-contrast T1maps with 11±08%LV (p=0.02). When referenced to normal values of healthy volunteers size of myocardial fibrosis was significantly lager with 35±4%LV on native T1, 49±26%LV on postcontrast T1 and 61±16%LV on ECV maps compared to values referenced to normal appearing myocardium (P<0.01, Figure 1). Mean ECV referenced to normal appearing myocardium was with 62±17% larger compared to ECV of 42±12%, when referenced to healthy volunteers (p<0.01). Conclusions: When referenced to normal appearing myocardium similar fibrosis sizes were obtained by LGE and ECV, but smaller fibrosis sizes were measured by native and post-contrast T1. Significantly larger fibrosis sizes were found with all mapping techniques when measurements were referenced to normal values of healthy volunteers, indicating a much larger fibrosis burden in HCM patients than currently observed with LGE imaging. (Figure Presented).