Imagine, believe, and achieve

Abstract

Cardiac amyloidosis was an under-recognized and undertreated disease until some years ago. Multimodality imaging plays a key role in the diagnosis of this progressive infiltrative cardiomyopathy, in addition to the clinical picture, endomyocardial/fat pad biopsies, and serum cardiac biomarkers. Although echo and cardiac magnetic resonance (CMR) provide structural and functional data, but neither can provide a distinction between transthyretin amyloid cardiomyopathy (ATTRCM) and light chain amyloid cardiomyopathy (AL-CM). Among imaging techniques, scintigraphy with bone-avid tracers: technetium-99m-3,3-diphosphono1,2-propanodicarboxylic acid (Tc-DPD) and hydroxymethylene diphosphonate (Tc-HMDP) 1–3 and technetium-99m pyrophosphate (Tc-PYP), mainly used in Canada, US, and Latin America, has emerged as a very sensitive and specific test to diagnose transthyretin amyloidosis (ATTR). It makes possible to differentiate ATTR from cardiac light chain amyloidosis (AL) non-invasively, with a significant accuracy and a 100% positive predictive value, mainly when performed with adjunctive clonal analysis with free light chain immunofixation to exclude AL amyloidosis. If TTR amyloidosis is diagnosed, a genotype testing is important to differentiate between wild-type (non-mutant) (ATTRwt) or mutated transthyretin (ATTRm) (hereditary form). In the consensus recommendations, the appropriate clinical scenarios where bone scintigraphy with 99mTcPYP, -DPD, and -HMDP should be used are summarized: evaluation in asymptomatic TTR gene carrier, individuals[ 60 years old with low-flow low-gradient aortic stenosis, unexplained heart failure, and increased wall thickness (especially in people of African American origin), individuals with heart failure and unexplained sensorimotor neuropathy, and individuals with known or suspected familial amyloidosis. However, the pathway to achieve a proper monitorization of treatment as well as the evaluation of the response to the new drugs already used is not so defined. New imaging approaches considering contrast-enhanced-cardiac magnetic resonance (CE-CMR) imaging with T1 mapping and molecular targeted imaging with 18fluorine (F) florbetapir positron emission tomography (PET) potentially provide a more accurate estimation of cardiac amyloid burden compared with echocardiography, standard late gadolinium enhancement (LGE), or SPECT. Global and regional LV extracellular volume fraction (ECV) is significantly expanded in amyloid hearts as a result of amyloid infiltration. Florbetapir is a stilbene derivative that binds to AL and ATTR deposits in human hearts ex vivo and in vivo, and molecular amyloid PET makes possible the global and regional quantification of the cardiac amyloid burden. Although the evaluation of myocardial uptake on Tc-PYP and Tc-DPD scintigraphies is based on a visual interpretation by means of Perugini scores using planar imaging, as well as a semiquantitative assessment using the heart-to-contralateral lung (H/CL) ratio with reasonable results, enough for a cardiac ATTR diagnosis, the visual and semiquantitative assessment is not able neither to properly stratify prognosis nor to assess disease progression or therapeutic response. Thus, quantification of SPECT radiotracers is also being explored using SPECT/CT images, by means of calculation of indexes such as SUVmax, SUVpeak, and SUVmax and SUVpeak normalized to bone activity Reprint requests: Amalia Peix, MD, PhD, FACC, ASNC, Nuclear Medicine Department, Institute of Cardiology, 17 No. 702, Vedado, La Habana, CP 10 400, Cuba; [email protected] J Nucl Cardiol 2021;28:831–4. 1071-3581/$34.00 Copyright 2021 American Society of Nuclear Cardiology.