Acute limb ischaemia revealing AL cardiac amyloidosis despite sustained sinus rhythm: a case report.

BACKGROUND: Thromboembolic complications are well recognized in cardiac amyloidosis and are traditionally attributed to atrial fibrillation (AF). However, patients with immunoglobulin light-chain (AL) cardiac amyloidosis remain at substantial thromboembolic risk, even in sinus rhythm, presumably due to atrial mechanical dysfunction. Acute limb ischaemia as the first clinical manifestation of AL cardiac amyloidosis is exceedingly rare. CASE SUMMARY: A 64-year-old man presented with sudden-onset pain and coldness in the left lower limb. Computed tomography revealed acute occlusion of the left popliteal artery, and an emergency surgical thrombectomy was successfully performed. Electrocardiography showed sinus rhythm, and continuous monitoring during hospitalization detected no atrial fibrillation. Transthoracic echocardiography demonstrated concentric ventricular wall thickening and reduced transmitral A-wave velocity despite preserved sinus rhythm and generally normal left atrial size, suggesting impaired atrial mechanical function. Cardiac magnetic resonance imaging revealed diffuse subendocardial late gadolinium enhancement extending into the left atrial myocardium. Right ventricular endomyocardial biopsy confirmed AL amyloidosis. The patient was accordingly diagnosed with AL cardiac amyloidosis, complicated by systemic arterial thromboembolism. Daratumumab-based therapy and anticoagulation were initiated, resulting in no recurrence of embolic events and excellent functional recovery during follow-up. DISCUSSION: This case highlights that AL cardiac amyloidosis can cause clinically significant systemic arterial thromboembolism, even in apparent sinus rhythm. Atrial mechanical dysfunction due to amyloid infiltration, rather than atrial fibrillation, appears to be a key mechanism. Clinicians should consider cardiac amyloidosis in patients with embolic events of unknown origin, particularly when imaging findings suggest infiltrative cardiomyopathy.