Effect of Trimetazidine on Coronary Flow in Transthyretin Cardiac Amyloidosis

The goal of this clinical trial is to learn if trimetazidine can improve blood flow in the heart in adults with transthyretin cardiac amyloidosis (ATTR-CM). ATTR-CM is a condition in which an abnormal protein builds up in the heart and can make it harder for the heart to work normally. The main question this study aims to answer is: Does trimetazidine improve the heart's ability to increase its blood flow when more blood is needed? The study will also look at whether treatment is linked to changes in walking ability, heart-related blood tests, heart function, and quality of life. Participants will: Take trimetazidine for about 6 months. Have heart blood flow measured with a positron emission tomography/computed tomography (PET/CT) scan before and after treatment. Have heart ultrasound examinations and blood tests. Complete a 6-minute walk test and a questionnaire about their symptoms and quality of life.

Inclusion Criteria: * Diagnosis of transthyretin cardiac amyloidosis confirmed by all protocol-specified diagnostic criteria or by Congo red-positive tissue biopsy with cardiac involvement. The diagnostic criteria listed in the current protocol include: * Interventricular septal thickness \>12 mm on echocardiography or cardiac magnetic resonance imaging, in the absence of other causes of hypertrophy (e.g., hypertension or aortic stenosis) * History of signs or symptoms of heart failure consistent with cardiac amyloidosis * Cardiac scintigraphy with technetium-99m pyrophosphate showing grade II or III uptake according to the Perugini scale * Age \>18 years * New York Heart Association (NYHA) functional class II, III, or IV Exclusion Criteria: * Previous adverse reaction, intolerance, or other contraindication to trimetazidine * Serum kappa/lambda ratio outside the normal range * Use of calcium channel blockers, beta-blockers, or nitrates * Obstructive coronary artery disease, defined as \>50% stenosis in any major epicardial coronary artery, demonstrated by coronary computed tomography angiography * Active infection, inflammatory disease, or other systemic condition that may affect myocardial perfusion * Contraindication to dipyridamole or PET/CT imaging * Estimated glomerular filtration rate \