Abstract 4358919: Apical sparing of echocardiographic strain in transthyretin amyloidosis is not explained by reduced infiltration of amyloid as determined by technetium-99m pyrophosphate uptake

Background: Cardiac amyloidosis is classically described as having an apical sparing pattern by strain calculations on transthoracic echocardiography (TTE) which has been attributed to sparing of amyloid deposition in the left ventricular apex. Likewise, we have frequently observed relative sparing of the anteroapical wall on technetium-99m pyrophosphate (PYP) scanning in patients who show scintigraphic evidence for transthyretin amyloidosis (ATTR). Hypothesis: We hypothesized that patients with apical sparing on TTE would have less amyloid infiltration of the apex as manifested by decreased PYP uptake in this region. Methods: In this retrospective study, patients with 3+ PYP scans and diagnosed with ATTR were included if they had a TTE within 2 years of the PYP. Blinded analysis of TTE and PYP images were performed by experienced cardiologists at an academic center. Apical sparing on TTE was defined as relative apical longitudinal strain (RALS) ≥ 1. RALS was calculated using the formula average apical LS / (average basal LS + average mid-ventricular LS). Volume weighted, normalized bullseyes were constructed from the single-photon emission computed tomography PYP images. Apical activity was defined as average counts in the 10% of the ventricle surrounding the apex. Independent samples t-test and linear regression were performed using SPSS. Results: 42 patients were included in the study. 33 (78.6%) were male and 9 (21.4%) were female. RALS was ≥ 1 in 19 patients (45.2%). Average counts in the apex in all patients ranged from 24-92 with a mean of 63.3 (± SD 17.7). Average counts in the apex were 65.7 (± SD 16.3) vs. 61.3 (± SD 18.9) for patients with RALS ≥ 1 vs. RALS < 1 (p=0.431). RALS on TTE did not correlate with average counts in the apex on PYP (R = 0.210, p = 0.091). Conclusion: The pattern of apical sparing by TTE strain measurements appears to have a different mechanism than decreased amyloid infiltration as determined by PYP.