Abstract
BACKGROUND: Transthyretin amyloid cardiomyopathy (ATTR-CM) is usually characterized by left ventricular (LV) hypertrophy or LV systolic dysfunction. However, right atrial (RA) amyloidosis without LV hypertrophy, leading to severe functional tricuspid regurgitation (FTR), is extremely rare. CASE SUMMARY: We present 75-year-old female with exertional dyspnoea and pre-syncope. Transthoracic echocardiography showed a normal LV function and no LV hypertrophy. A sick sinus syndrome and severe FTR due to right ventricular (RV) and RA dilatation were observed. A leadless cardiac pacemaker implantation was performed for sick sinus syndrome and the symptoms improved, but she complained of leg oedema and fatigue on effort again. A repeated transthoracic echocardiogram showed no notable changes in LV function, but progression of RV and RA dilatation was observed, with worsening FTR. Despite treatment of loop diuretics with 30 mg daily of azosemide, symptoms did not improve, and the patient underwent tricuspid valve annuloplasty. Pathological findings from right atrium led to a diagnosis of ATTR-CM, and deoxyribonucleic acid sequence analysis did not indicate any typical mutation, which supported a diagnosis of wild type of ATTR-CM (ATTRwt-CM). She has been asymptomatic after the surgical operation. She has also been treated with 80 mg daily of tafamidis meglumine to prevent further accumulation of transthyretin in the myocardium and potentially improve long-term outcomes. DISCUSSION: Isolated atrial amyloidosis, especially occurring predominantly in the right atrium and caused by ATTRwt-CM without LV hypertrophy, is extremely rare. However, differential diagnosis should be considered for patients with unexplained dilatation of the right-sided heart or bradyarrhythmia.