Extracellular matrix expansion by cardiac magnetic resonance T1 mapping- validation with myocardial biopsy

Abstract

Background Accumulation of diffuse myocardial fibrosis / extracellular volume (ECV) in the myocardium is common to various cardiac diseases and is associated with an unfavorable prognosis. Various cardiac magnetic resonance (CMR) T1 mapping techniques have recently been proposed for the quantification of ECV, including: 1. Modified Look-Locker Inversion recovery (MOLLI) T1 mapping including calculation of ECV, 2. Post-contrast multiple-breath-hold T1 mapping. 3. Native (precontrast) T1 mapping. T1 mapping is a promising technique, however, validation data based on myocardial biopsy are sparse. Methods 36 heart failure patients underwent CMR T1 mapping and left-ventricular biopsy within 4 weeks. CMR protocols (1.5-T scanner, (Magnetom Avanto, Siemens Healthcare, Erlangen, Germany) included non-product MOLLI and multiple-breath-hold T1 mapping. The population consisted of 22 patients with HFpEF (heart failure with preserved ejection fraction), 7 with cardiac amyloidosis, 3 with HFrEF (heart failure with reduced ejection fraction) and 4 with organic mitral regurgitation (MR). Specimens were stained using modified Trichrome. TissueFAXS and dedicated software were used to quantify ECV. Results ECV by TissueFAXS was 32±17% and 35±13% by CMR MOLLI. Post-contrast T1 times by the multiple-breathhold sequence were 411±79ms, native T1 times were 1009±73ms. Patients with amyloidosis had significantly more ECV by TissueFAXS (59±13%, p<0.001) and with CMR MOLLI (56±12%, p<0.001) compared with the other pathologies. The amount of TissueFAXS ECV correlated significantly with native T1 times (r=0.657, p<0.001), MOLLI ECV (r=0.907, p<0.001) and with multiple-breath-hold post-contrast T1 times (r=-0.683, p<0.001). When excluding patients with amyloidosis, only MOLLI ECV significantly correlated with histology (r=0.491, p=0.015), whereas multiple-breath-hold post-contrast T1 times just missed the level of significance (r=-0.413, p=0.056).