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2411. Quantification of Myocardial Radiotracer Uptake in Cardiac Scintigraphy for Cardiac ATTR Amyloidosis
Authors * Denotes Presenting Author
  1. Francis Delaney *; Mater Misericordiae University Hospital
  2. Martin O'Connell; Mater Misericordiae University Hospital
Objective:
Cardiac transthyretin (ATTR) amyloidosis has emerged as an under-recognised cause of heart failure in elderly patients in recent years. In addition, multiple novel therapies have begun to emerge for this morbid and previously fatal disease. As a result, there has been growing interest in the early identification of ATTR amyloidosis to facilitate early treatment initiation. Large number of studies in the past decade have led to development of new consensus recommendations for the investigation of suspected ATTR amyloidosis. Cardiac scinitgraphy plays a key role in these new diagnostic algorithms. Multiple technetium 99m (Tc99m)-labelled bone scinitigraphy radiotracers, such as 3,3-diphoshono-1,2-propanodicarboxylic acid (DPD), reliably identify myocardial ATTR amyloid deposition. Significant (Perugine grade 2 or 3) myocardial uptake is diagnostic for ATTR amyloidosis where systemic AL amyloidosis has been excluded biochemically. As novel TTR gene therapies are introduced into clinical practice, reliable non-invasiveness methods to quantify myocardial ATTR amyloid burden over time are required to allow assessment of disease progression and treatment response. We aimed to map the distribution and extent of myocardial DPD uptake in ATTR amyloidosis using commercially available myocardial perfusion imaging (MPI) quantification software. The polar plot data which is produced may enhance understanding of the distribution of DPD uptake and help quantify severity over serial studies.

Materials and Methods:
Tc99m-DPD radionuclide studies to evaluate for cardiac ATTR amyloidosis in 26 patients who demonstrated significant uptake (graded as Perugini Score 2 or 3) on planar thoracic imaging were included. Additional SPECT imaging was performed in all cases. Images were analysed using AutoQUANT® software (Cedars Sinai, CA) and polar plot maps were produced based on the 20-segment model with relative uptake quantified in each segment from 0-100. Data was compared to echocardiographic and MRI findings. Where available, polar plot uptake on serial patient studies was compared to assess for progression over time.

Results:
Quantification was successful in all patients. Polar plot evaluation demonstrated an apical and septal predominance in the left ventricular myocardial distribution of radiotacer accumulation. Follow-up imaging available to date has shown the potential to demonstrate a change in the extent of myocardial radiotracer accumulation using polar plot quanitification.

Conclusion:
The use of cardiac scintigraphy in ATTR amyloidosis continues to expand beyond its role in initial diagnosis with potential applications in screening of high risk groups, in prognostication and in follow-up of disease progression proposed. We have demonstrated the ability to re-purpose standard commercially available software to assess left ventricular myocardial uptake of Tc99m DPD in ATTR amyloidosis. While increased follow-up studies and formal validation are required, there is the possibility to improve the quantification of DPD uptake, map its distribution and assess objectively for progression over time.