Abstract Body (Do not enter title and authors here): Background: Initiation of Guideline-Directed Medical Therapy (GDMT) in patients who have heart failure with reduced ejection fraction (HFrEF) has been shown to improve left ventricular EF, decrease hospitalizations, and reduce mortality. GDMT includes an angiotensin receptor/neprilysin inhibitor (ARNI). However, the relative importance of initiating or maintaining ARNI therapy during titration of GDMT and the impact on changes in left ventricular (LV) and right ventricular (RV) function is unknown.

Methods: We enrolled 173 patients with HF in a GDMT clinic prospectively between 2020 to 2022. Of 173 patients, 63 HFrEF patients with baseline and 3-12 months follow-up transthoracic echocardiography (TTE) were included in this post-hoc analysis. Patients were divided into three groups; patients with initiation of ARNI after baseline TTE (Group 1), patients with continuation of ARNI that was started before baseline TTE (Group 2), patient who were not on ARNI during evaluation period (Group 3). LVEF as calculated by volumetric assessment, LV global longitudinal strain (LVGLS), RV fraction area change (RVFAC), and RV global longitudinal strain (RVGLS) were evaluated in this study. Strain analysis of LVGLS and RVGLS were applied using TomTec.

Results: The mean age was 64 years, the mean time between TTEs was 6.9 months. Improvement in biventricular function and strain were noted between baseline and follow up data. (Figure 1) Changes of the four parameters for each group between the two TTEs are shown in Figure 2. In patients initiated on ARNI therapy (Group 1) there was a significant improvement from baseline to follow up TTEs in all parameters. (LVEF; p < 0.001, LVGLS; p < 0.001, RVFAC; p = 0.003, and RVGLS; p = 0.003) In group 2, we noted significant improvements in LVEF, LVGLS, and RVGLS from baseline to follow up. (LVEF; p < 0.001, LVGLS; p < 0.001, and RVGLS; p = 0.005) In those not on ARNI (Group 3), there was no statistical difference noted in any of the 4 parameters between baseline and follow up TTE.

Conclusion: In patients with HFrEF, who had routing follow-up in a GDMT clinic, those initiated or continued on ARNI had significant improvement in biventricular function and biventricular strain measurements, compared to those who were not taking an ARNI.