higher rates of EKG criteria for LVH, RVH or both and were more likely to require advanced therapies such as ICD placement and cardiac trans- plant. Larger studies involving WPW in Danon Disease should seek to bet- ter characterize these outcomes. (368) Cardiac Autonomic Nerves Stimulation Improves Hemodynamics and Clinical Status in Advanced Heart Failure Patients T. Diaz, 1 C. Marin y Kall, 2 J. Boehmer, 3 M. Cowie, 4 A. Mebazaa, 5 and M. Cuchiara. 6 1 Pacífica Salud Hospital Punta Pacífica, Panama City, Panama; 2 International Medicine Institute, University of Miami, Miami, FL; 3 Penn State Hershey Heart and Vascular Institute, Hershey, PA; 4 Imperial College London, London, United Kingdom; 5 Department of Anesthesiology and Critical Care, University Paris Diderot, Paris, France; and the 6 NeuroTronik Inc, Durham, NC. Purpose: Despite heart failure therapy advances, symptomatic congestion and low cardiac output in acute heart failure is a leading cause of mortality and morbidity. The purpose of this study was to investigate transvenous cardiac autonomic nerve stimulation (CANS) effects on in-hospital hemo- dynamics and clinical status. Methods: The study was a single-center, open label, clinical investigation of CANS. Twenty two subjects with LVEF <40% and at least two signs and symptoms of congestion were consented and enrolled. A purpose- built electrical stimulation catheter was placed in the left brachiocephalic vein via left subclavian vein access and connected to a purpose-built bed- side neurostimulator used to deliver CANS therapy in-hospital for up to 96 hrs. Results: The subjects had a mean baseline NT-proBNP of 10,518 pg/mL, LVEF of 25%, pulmonary capillary wedge pressure (PCWP) of 20 mmHg and presented with symptoms. CANS therapy was provided for a mean duration of 70 hrs. There were no device or study related adverse events reported. During CANS therapy mean cardiac index increased (1.8 to 2.0 L/min./m 2 ), mean systemic vascular resistance decreased (24 to 20 WU), and mean PCWP decreased (20 to 14 mmHg) with stable MAP and HR. At discharge, mean edema pitting score improved 2 points, mean 6 minute hall walk distance (6MHW) increased 92 m and mean KCCQ-12 increased 12 points. At 30 day follow-up, edema pitting score improved 3 points, 6MHW increased 102 m and mean KCCQ-12 improved 38 points from baseline. Hemodynamic and clinical improvements occurred in the presence of stable medical management. Patients received at least 80 mg/day of furosemide, had minimal change to existing heart failure medical management, received no new IV vasoactive therapies, and a majority of the patients (17/22) received no furosemide dose uptitration during CANS Therapy. Conclusion: Alongside concomitant medical therapy, CANS holds prom- ise as a tool to improve in-hospital hemodynamics and relieve congestion. (369) Estimation of Mean Arterial Pressure Using Doppler and Pump Parameters in HeartMate 3 Patients A. Pinsino, 1 G.M. Mondellini, 2 F. Castagna, 2 A. Gaudig, 2 M. Yuzefpolskaya, 2 N. Uriel, 2 G. Sayer, 2 K. Takeda, 3 Y. Naka, 3 J.R. Cockcroft, 4 E.J. Stohr, 4 B. McDonnell, 4 and P.C. Colombo. 2 1 Medicine, Albert Einstein College of Medicine, NYC Health + Hospitals/Jacobi, New York, NY; 2 Cardiology, Columbia University Medical Center, New York, NY; 3 Surgery, Columbia University Medical Center, New York, NY; and the 4 Biomedical Sciences, Cardiff Metropolitan University, Cardiff, United Kingdom. Purpose: The optimal method for blood pressure (BP) measurement among pts implanted with HeartMate 3 (HM3), a centrifugal pump that features an artificial pulse, is presently unknown. We aimed to: 1) assess success rate and validity of Doppler opening BP (DOBP) and automated BP (ABP) monitor; 2) test a novel approach to estimate mean arterial pres- sure (MAP) by combining DOBP and HM3 parameters. Methods: BP and HM3 parameters (Speed, Power, Pulsatility Index [PI], Flow) were prospectively collected in a derivation cohort (DC, n=50) and a validation cohort (VC, n=11). BP was measured by arterial line (A-line) in all pts. DOBP and ABP were concurrently measured in a subgroup of DC (DCs, n=31) and in VC. In DC, a multiple linear regression model was fit with A-line systolic BP (SBP) and HM3 parameters as predictor varia- bles and A-line MAP as the dependent variable to derive the HM3 MAP Formula. In DCs and VC, the accuracy of the Formula in estimating A- line MAP was tested using DOBP as non-invasive equivalent of A-line SBP. Mean observed differences (MOD) and mean absolute differences (MAD) against A-line were calculated for each method. Results: The success rate for Doppler and ABP monitor was 100% and 49%, respectively. In DCs, DOBP reflected A-line SBP (MAD 4.6, MOD +1.7 mmHg) but markedly overestimated A-line MAP (Fig A). MAD and MOD of ABP monitor were 7.7 and +3.5 and 7.0 and +1.1 mmHg for SBP and MAP, respectively (Fig B). In DC, the best model to predict A-line MAP included PI and Flow in addition to A-line SBP (HM3 MAP For- mula,r 2 =0.77). In DCs, the Formula accurately predicted A-line MAP when using A-line SBP (Fig C) and DOBP (Fig D). In a preliminary analy- sis of VC, the accuracy of the Formula was similar (MAD: A-line SBP 4.1, DOBP 6.8 mmHg). Conclusion: In HM3 pts, DOBP accurately estimates SBP, but overesti- mates MAP. ABP monitor has limited success rate and accuracy, possibly due to the artificial pulse. The HM3 MAP Formula represents a uniformly successful and valid tool to estimate MAP by combining DOBP and pump parameters. (370) Variability in Blood Pressure Assessment in Patients Supported with HeartMate 3 J.A. Cowger, 1 J.D. Estep, 2 D.A. Rinde-Hoffman, 3 M.M. Givertz, 4 A.S. Anderson, 5 D. Jacoby, 6 L. Chen, 7 A. Brieke, 8 C. Mahr, 9 S. Hall, 10 G.A. Ewald, 11 A. Baker, 12 J. Chuang, 12 and S.P. Pinney. 13 1 Cardiovascular Medicine, Henry Ford Hospital, DETROIT, MI; 2 Cardiovascular Medicine, Cleveland Clinic, Cleveland, OH; 3 Tampa General Med Grp, Tampa, FL; 4 Brigham & Women's Hosp, Boston, MA; 5 Northwestern University Bluhm Cardiovascular Institute, Chicago, IL; 6 Yale School of Medicine, New Haven, CT; 7 University of Rochester, Rochester, NY; 8 University of Colorado School of Med, Denver, CO; 9 University of Washington, Seattle, WA; 10 Baylor University Medical Center, Dallas, TX; 11 Washington University, St. Louis, MO; 12 Abbott, Inc, Abbott Park, IL; and the 13 Cardiovascular Medicine, Icahn School of Medicine at Mount Sinai, New York, NY. Purpose: Targeted blood pressure (BP) control is a goal of LVAD medical management, but the interpretation of values obtained from automated cuffs and Doppler opening pressure (DOP) is challenging. The aim herein S156 The Journal of Heart and Lung Transplantation, Vol 39, No 4S, April 2020