Atrial Flutter Revealing Transthyretin Cardiac Amyloidosis : Diagnostic and Therapeutic Management – A Case Report and Literature Review

Abstract

Transthyretin cardiac amyloidosis is an infiltrative cardiomyopathy that may present with atrial arrhythmias, bradycardia, and heart failure. We report a 73-year-old patient with bilateral carpal tunnel syndrome and Horton disease who was admitted with decompensated right-sided heart failure, marked lower-limb oedema, and asymptomatic bradycardia. Electrocardiography showed slow typical atrial flutter at 45 beats per minute. Transoesophageal echocardiography excluded atrial thrombus, and cavotricuspid isthmus radiofrequency ablation restored sinus rhythm. Transthoracic echocardiography demonstrated concentric left ventricular hypertrophy, a speckled myocardial appearance, restrictive filling, biatrial dilatation, and elevated pulmonary artery pressure. Serum free light-chain testing was normal, while technetium-99m bone scintigraphy showed intense myocardial uptake consistent with Perugini grade 3 transthyretin cardiac amyloidosis. Diuretic therapy improved the congestive symptoms, and tafamidis was initiated. Post-ablation Holter monitoring revealed first-degree atrioventricular block, chronotropic incompetence, blocked premature atrial contractions, and intermittent second-degree atrioventricular block. A dual-chamber pacemaker with left bundle branch area pacing was therefore implanted. At 6 months, the patient maintained good functional status without recurrent heart failure decompensation. This case illustrates that slow typical atrial flutter and conduction-system disease may reveal transthyretin cardiac amyloidosis. Recognition of extracardiac red flags, systematic diagnostic assessment, rhythm control, disease-specific therapy, and individualised physiological pacing supported the favourable clinical course.