ECV per unit of myocardial thickness as a potential sign of transthyretin cardiac amyloidosis on CMR

Abstract Background/Introduction CMR is often employed to assess patients with unexplained left ventricular hypertrophy (LVH), which may be caused by transthyretin cardiac amyloidosis (TTR-CA). Expansion of extracellular volume (ECV) is hallmark of CA. As ECV equalizes or becomes greater than hematocrit level, a specific pattern of late gadolinium enhancement (LGE) on cardiac magnetic resonance (CMR) is seen. However, it is a sign of late-stage disease and early identification of TTR-CA by CMR is challenging. Purpose To identify early signs of TTR amyloid cardiomyopathy by CMR. Methods We retrospectively analyzed a cohort of patients with confirmed wild-type transthyretin CA (TTR-CA) with available CMR scans (Siemens MAGNETOM Skyra, 3T) to identify patients who did not present with classical CMR LGE pattern – early TTR-CA group. A comparison of LV ejection fraction (LVEF), right ventricular EF (RVEF), LV myocardial mass index (MMI), ECV and ECV per millimeter of LV thickness (average of basal and mid-ventricular ECV divided by average of basal and mid-ventricular wall thickness) was made between early and classical TTR-CA groups, as well as with cohort with different forms of LVH: gene-positive hypertrophic cardiomyopathy (HCM) and severe aortic stenosis (AS). Results Out of 28 patients with TTR-CA (68% males, median age 73 [68-78]), 5 patients (80% females, median age 75) presented without classical signs of CA on LGE CMR (early CA group). Comparison between early CA and classical CA groups revealed significant differences in LVEF (60.6±5.5% vs 50.7±8.1%, p=0.01), RVEF (67.8±2.3% vs 57.6±12%, p=0.01), LV MMI (68±18.8 g/m2 vs 106±22 g/m2, p=0.01), and ECV (32.0±2.3% vs 47.68±9.9%, p