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Funding Acknowledgements Type of funding sources: None. Introduction Systemic sclerosis (SSc) can cause cardiac complications as a result of multi-organ fibrosis. The study of left atrial (LA) mechanics can offer insights into the pathophysiology of cardiac involvement in SSc. LA strain measured by speckle-tracking echocardiography (STE) has been shown to be a sensitive marker of LA function. The impact of a disease modifying treatment like hematopoietic stem cell transplant (HSCT) on LA mechanics is not known. Aim To study the effect of HSCT on LA mechanics using both conventional echocardiography and STE. Methods Patients with SSc who underwent comprehensive 2D echo evaluation pre- and post-HSCT were identified. Patients with pulmonary hypertension on right heart catheterization (RHC) were excluded. The modified Rodnan skin score (mRSS) was evaluated for each patient pre- and post-HSCT. Speckle tracking software was utilized to measure myocardial strain (TomTec, Unterschleissheim, Germany). LA reservoir strain was measured from the apical 2-, and 4-chamber views. The ratio of E/e’ to LA reservoir strain was used to non-invasively estimate LA stiffness. Paired student’s t-test and Pearson"s correlation were used in data analysis. Results Among 89 patients with SSc (average age 46 ± 11 years, 75% female) who underwent HSCT, the mRSS significantly improved after HSCT. The mean pulmonary capillary wedge pressure (PCWP) measured by RHC prior to HSCT was 9.6 ± 4.1 mmHg. LA reservoir strain was abnormal at baseline and significantly improved following HSCT. Although LA volume index and E/e’ remained unchanged, LA stiffness index decreased significantly post-HSCT. There was no correlation between LA reservoir strain and PCWP at baseline or between change in LA reservoir strain and change in LA volume index or E/e’. Conclusions Patients undergoing HSCT for SSc show significant improvement in LA reservoir strain and LA stiffness despite no significant change in LA volumes or estimates of LV filling pressures. This improvement in LA mechanics following HSCT thus appears to be independent of loading conditions and could represent an improvement in intrinsic LA performance. Key clinical and echo characteristics Pre-HSCT Post-HSCT P value Median mRSS (25th - 75th percentile) 20 (13-34) 9 (4-20)

Funding Acknowledgements Type of funding sources: None. Introduction Systemic sclerosis (SSc) is an autoimmune disorder that causes fibrosis in the skin and internal organs, including the heart. Patients with SSc can have right ventricular (RV) systolic dysfunction in the absence of pulmonary hypertension. Studies have shown a predilection for impairment of the mid and apical segments of the RV free wall compared to controls. The effect of hematopoietic stem cell transplant (HSCT) – a disease modifying treatment for SSc – on RV mechanics is not known. Aim To study the effect of HSCT on RV mechanics using speckle-tracking echocardiography. Methods Patients with SSc who underwent comprehensive 2D echocardiographic evaluation pre- and post-HSCT were identified. The modified Rodnan skin score (mRSS) was evaluated for each patient pre- and post-HSCT. Speckle tracking software was utilized to measure myocardial strain (TomTec, Unterschleissheim, Germany). RV strain was measured from the RV focused apical 4-chamber view. Paired student’s t-test and linear regression analysis were used in data analysis. Results Among 89 patients with SSc (average age 46 ± 11 years, 75% female) who underwent HSCT, the mRSS significantly improved after HSCT. The mean pulmonary arterial pressure measured by right heart catheterization prior to HSCT was 18.5 ± 4.5 mmHg. There was a significant improvement in RV global longitudinal strain (GLS) and free wall strain (FWS) following HSCT. The improvement in strain was significant in the mid and apical segments of the RV free wall, but not so in the basal segment. The change in RV strain was linearly related to pre-HSCT strain. The lower the RV GLS and FWS, the greater the improvement in strain after HSCT. Conclusions There was a significant improvement in RV strain in patients undergoing HSCT, specifically within the mid and apical segments of the RV free wall. The improvement in strain after HSCT was directly related to the baseline strain. This suggests that HSCT may directly improve RV mechanics with the preferential enhancement of the less robust mid and apical RV free wall segments. Key clinical and echo characteristics Pre-HSCT Post-HSCT P value Median mRSS (25th - 75th percentile) 20 (13-34) 9 (4-20)