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Abstract 4621 Background: Primary systemic amyloidosis (AL) is a severe plasma cell disorder characterized by amyloid fibrils extracellular deposition in different organs. Myocardial involvement is frequent and has major impact on prognosis. Echocardiography (TTE) is the most common test performed when cardiac involvement is suspected. We hypothesized that a simple measurement of left atrium enlargement (LA) by TTE may provide an important risk marker for this disease. Methods and results: Between 1997 and 2010, 114 patients were diagnosed with systemic AL. Sixty one patients of the cohort (54%) had cardiac involvement on the basis of standard criteria defined as: mean LV wall thickness >12mm with no other cardiac causes. They had first TTE within 16 days of diagnosis. Patients were mainly treated with conventional chemotherapy (M-Dex) or with new agents for refractory or relapsing patients We retrospectively collected demographic baseline characteristics along with biological and echo data of these patients. Mean age was 61±11 years; 60% were male; 19% had hypertension. Mean left ventricular ejection fraction and mean LV wall thickness were respectively 58±13% and 15±3 mm. Mean follow up time was 2.1±2 years. None had significant valvular heart disease. LA enlargement was defined by M mode as > 40 mm in male and > 36 mm in female. Patients with enlarged LA had significantly more hypertension and lower ejection fraction and more hypertrophied LV walls (All P< 0.05). At 3 years, survival rate was markedly reduced in patients with enlarged LA vs. those with normal LA: 34±9% vs.75 ±9% (P =0.02). By multivariate analysis, after adjusting for age, gender, and presence of hypertension, LA enlargement remained an independent predictor of overall mortality at 3 years (HR=2.88; CI (1.12-8.84); P=0.03). Conclusion: In patients with systemic AL amyloidosis and cardiac involvement, LA enlargement, a surrogate marker of diastolic dysfunction and elevated LV filling pressure, is a powerful independent predictor of long-term mortality. Therefore LA enlargement may help to enhance risk stratification in patients presenting with this disease. Disclosures: No relevant conflicts of interest to declare.