BACKGROUND: Left atrial (LA) is crucial in the pathophysiology of cardiac amyloidosis (CA). Left atrial stiffness index (LASI) assesses LA function effectively, but related studies are limited. This study aims to assess LASI's prognostic values in CA patients. METHODS: In this retrospective analysis, 53 patients diagnosed with CA between 2018 and 2024 were included, alongside 53 healthy volunteers from the same period as the control cohort. Follow-up extended until July 31, 2024, or the patient died. Throughout the follow-up period, occurrences of major adverse cardiac events (MACE), encompassing all-cause mortality or hospitalization for heart failure, were documented. LASI was calculated as the ratio of the early diastolic peak velocity of the mitral valve to the average early diastolic peak flow velocity of the septal and lateral mitral annulus [E/e]/LASr (left atrial reservoir longitudinal strain). RESULTS: Over a 44 (22, 58) months follow-up, 43 % of patients experienced MACE, with 17 % passed away. The LASI in patients with CA showed a significant increase compared to the control group, with LASI being notably higher in the MACE group than the NO MACE group (all p <
0.001). Patients with lower LASI experienced more favorable clinical outcomes during the follow-up period compared to those with higher LASI (P <
0.001). Univariate and multivariate COX regression analyses both demonstrated that an increase in LASI was independently linked to a higher risk of MACE and all-cause mortality. CONCLUSION: LASI may be of prognostic value in CA patients by predicting both MACE and all-cause mortality.