Relative Apical Sparing of Myocardial Longitudinal Strain Is Explained by Regional Differences in Total Amyloid Mass Rather Than the Proportion of Amyloid Deposits

OBJECTIVES This study sought to test whether relative apical sparing (RELAPS) of left ventricular (LV) longitudinal strain (LS) in cardiac amyloidosis (CA) is explained by regional differences in markers of amyloid burden (F-18-florbetapir uptake by positron emission tomography [PET] and/or extracellular volume fraction [ECV] by cardiac magnetic resonance (CMR)]. BACKGROUND Further knowledge of the pathophysiological basis for RELAPS can help understand the adverse outcomes associated with apical LS impairment. METHODS This was a prospective study of 32 subjects (age 62 +/- 7 years; 50% males) with light chain CA. All subjects underwent two-dimensional echocardiography for LS estimation and F-18-florbetapir PET for quantification of LV florbetapir retention index (RI). A subset also underwent CMR (n = 22) for ECV quantification. Extracellular LV mass (LV mass* ECV) and total florbetapir binding (extracellular LV mass* florbetapir RI) were also calculated. All parameters were measured globally and regionally (base, mid, and apex). RESULTS There was a significant base-to-apex gradient in LS (+/- 7.4 +/- 3.2% vs. +/- 8.6 +/- 4.0% vs. +/- 20.8 +/- 6.6%; p < 0.0001), maximal LV wall thickness (15.7 +/- 1.9 cm vs. 15.4 +/- 2.9 cm vs. 10.1 +/- 2.4 cm; p < 0.0001), and LV mass (74.8 +/- 21.2 g vs. 60.8 +/- 17.3 g vs. 23.4 +/- 6.2 g; p < 0.0001). In contrast, florbetapir RI (0.089 +/- 0.03 mmol/min/g vs. 0.097 +/- 0.03 mmol/min/g vs. 0.085 +/- 0.03 mmol/min/g; p = 0.45) and ECV (0.53 +/- 0.08 vs. 0.49 +/- 0.08 vs. 0.49 +/- 0.07; p = 0.15) showed no significant base-to-apex gradient in the tissue concentration or proportion of amyloid infiltration, whereas markers of total amyloid load, such as total florbetapir binding (3.4 +/- 1.7 mmol/min vs. 2.8 +/- 1.5 mmol/min vs. 0.93 +/- 0.49 mmol/min; p < 0.0001) and extracellular LV mass (40.0 +/- 15.6 g vs. 30.2 +/- 10.9 g vs. 11.6 +/- 3.9 g; p < 0.0001), did show a marked base-to-apex gradient. CONCLUSIONS Segmental differences in the distribution of the total amyloid mass, rather than the proportion of amyloid deposits, appear to explain the marked regional differences in LS in CA. Although these 2 matrices are clearly related concepts, they should not be used interchangeably. (C) 2019 by the American College of Cardiology Foundation.