Abstract Body (Do not enter title and authors here): Introduction: Systemic thrombolysis (ST) is the mainstay of treatment for acute massive pulmonary embolism (PE). Catheter directed therapy (CDT) has become more common in treatment of acute PE in patients with contraindications to ST. Half-dose ST (hdST) has also been utilized with similar efficacy and a lower risk of bleeding than full-dose ST (fdST). It is uncertain how right ventricular dysfunction (RVD) on transthoracic echocardiography (TTE) varies comparing all three modalities.

Research Question: How does RVD on TTE imaging in acute PE vary based on the thrombolytic modality?

Methods: We conducted a retrospective, multi-center cohort study using data from our institutional PE Response Team registry. TTE imaging was directly assessed to obtain parameters. Included patients were over 18 years old with TTE’s obtained after CDT, fdST, or hdST, excluding those missing key RVD parameters (TAPSE, S', RV ratio, RVOT VTI, RVOT notching, 60-60 sign). RVD was defined as threshold values met in two or more parameters. Between group univariate testing was performed using ANOVA, Student’s t-test, chi-squared, and Fisher’s exact test when appropriate for the entire cohort as well as specifically CDT vs. hdST.

Results: The final cohort included 188 patients, with 163 undergoing CDT, 19 receiving hdST, and 6 receiving fdST. Patients with hdST had significantly higher RVOT VTI (13.8 ± 5.7 cm) compared to the CDT group (10.7 ± 4.5 cm, p=0.016). There were lower rates of RVD in the hdST group (26.3%) compared to CDT (39.3%, p=0.04). Bleeding rates were not statistically different across all three cohorts (p=0.78)

Conclusion: Despite the higher severity of illness on presentation, patients treated with hdST had lower rates of RVD following treatment compared to those treated with CDT, without increased rates of bleeding. Further investigation is needed; however this study provides additional evidence supporting the safety of hdST in hospital systems lacking access to CDT.