Abstract Body: Background: TEE is increasingly recognized as a valuable imaging modality during cardiac arrest (CA) resuscitation, particularly for assessing the area of maximal compression (AMC) during CPR. Small single center studies have shown that compression of the left ventricular outflow tract or the aortic root (AMC-LVOT/Ao) is common during CPR, and that when CPR is performed with the AMC over the LV, this results in higher ETCO2, and ROSC. This study aimed to investigate the AMC and its relationship to ETCO2, and ROSC, hypothesizing that patients experiencing AMC-LVOT/Ao have lower ETCO2 and are less likely to achieve ROSC.

Methods: A prospective, multicenter cohort study of patients with out-of-hospital and in-hospital CA (OHCA/IHCA) in whom TEE was performed during CPR comparing AMC over the LV (AMC-LV) vs AMC-LVOT/Ao. The study was conducted through the Resuscitative TEE Collaborative Registry, an ongoing multicenter research network involving 37 hospitals (NCT04972526). Collected data included patient and procedure characteristics, hemodynamics, and outcomes according to Utstein-style guidelines. Primary outcome was ROSC, and the secondary outcome was ETCO2 at the time of AMC determination. We performed univariate analysis and multivariate regression evaluating variables known to impact resuscitation outcomes.

Results: 271 patients including 205 OHCA and 66 IHCA were included. Only 133 (49%) of the total cohort had AMC-LV, with AMC-LVOT/Ao in 47% of OHCA and 42.1% of IHCA. There was no significant difference in the location of the AMC when analyzed by demographic characteristics, height, weight, or comorbidities between patients who received manual vs mechanical CPR. In OHCA, there was no difference in ROSC between AMC-LV and AMC-LVOT/Ao, however the group of patients with AMC-LVOT/Ao had on average 10 units lower ETCO2 compared to AMC-LV (Beta -10; 95% CI -19 - 1.5; p = 0.023). In IHCA, after controlling for factors known to impact outcomes, patients with AMC-LVOT/Ao had significantly lower probability of ROSC (OR 0.25, 95% CI 0.06-0.88; p=0.038).

Conclusion: Obstruction of the LVOT/Ao during CPR is a common finding in CA patients evaluated with TEE. This multicenter study extends previous animal and smaller clinical studies suggesting the mechanistic association between the AMC during CPR, with ETCO2 and ROSC, and the potential of TEE-guided resuscitation to improve the effectiveness of CPR.