The goal of this study is to learn whether PET-CT imaging using evuzamitide can help diagnose transthyretin cardiac amyloidosis (ATTR-CA) in patients whose standard nuclear imaging results are unclear but who have elevated TAD1 levels in their blood. The main question it aims to answer is:

Can evuzamitide PET-CT imaging detect signs of cardiac amyloidosis in patients with non-diagnostic nuclear scintigraphy but elevated TAD1 levels? Participants who meet eligibility criteria will receive a single PET-CT scan with evuzamitide and will be followed for approximately 28 days to monitor safety and collect additional clinical information.

This is a prospective, multicenter observational study designed to evaluate the ability of 124I-evuzamitide PET-CT imaging to resolve the diagnosis of transthyretin cardiac amyloidosis (ATTR-CA) in subjects with discordant findings between nuclear scintigraphy and Transthyretin Amyloid Detector 1 (TAD1) levels.

Up to 25 participants will be enrolled across three sites in the United States, including the University of Texas Southwestern Medical Center, Columbia University Irving Medical Center, and Boston Medical Center. Participants will be selected from clinical registries and prior screening studies and must have non-diagnostic nuclear scintigraphy for ATTR-CA and elevated TAD1 levels.

Eligible participants will receive a single intravenous administration of approximately 1 mCi of 124I-evuzamitide, followed by PET-CT imaging performed approximately 4 hours post-injection. Potassium iodide will be administered before and after imaging to reduce thyroid exposure.

PET-CT images will be evaluated qualitatively and quantitatively for myocardial uptake of the tracer. Image interpretation will be performed by trained physicians, and discrepancies will be resolved by consensus review.

Safety will be assessed through adverse event monitoring, vital signs, and physical examinations, with follow-up conducted approximately 28 days after imaging.

Inclusion Criteria:

1. Diagnosed as having heart failure or TTR variant allele carriers without symptoms of heart failure.
2. Non-diagnostic nuclear scintigraphy for ATTR-CA (Perugini Grade 0 or 1).
3. Elevated levels of Transthyretin Amyloid Detector-1 (TAD1).
4. No evidence of monoclonal proteins by assessment of serum kappa and lambda free light chain ratio and immunofixation of serum and urine.
5. Must have given written informed consent (signed and dated) and any authorizations required by local law and be able to comply with all study requirements.
6. Able to understand and sign the informed consent document after the nature of the study has been fully explained.

Exclusion Criteria:

1. Primary amyloidosis (AL) or secondary amyloidosis (AA).
2. Ventricular assist device.
3. Disabling dementia or other mental or behavioral disease.
4. Enrollment in a clinical trial not approved for co-enrollment.
5. Continuous intravenous inotropic therapy.
6. Inability or unwillingness to comply with the study requirements.
7. Chronic kidney disease requiring hemodialysis or peritoneal dialysis.
8. Patients taking heparin, or heparin derivatives (e.g. low molecular weight heparins) for anticoagulation.
9. Other reason that would make the subject inappropriate for entry into this study.
10. Pregnancy or current lactational feeding of infants.

Participants will be drawn from clinical practice registries and epidemiological ATTR-CA screening projects at UT Southwestern, Columbia University Irving Medical Center, and Boston Medical Center