The goal of this feasibility study is to evaluated the safety and performance of the WhiteSwell eLym System in the treatment of fluid overload or congestion in adult patients with Acute Decompensated Heart Failure (ADHF). The main question[s] it aims to answer are:

• Acute device safety (30 days)
• Chronic device safety (31-180 days)
• Primary performance Outcomes (Technical success and patient treatment outcomes)

Participants who are hospitalized for ADHF will be screened for treatment with the eLym System. The System, placed in a heart catheterization laboratory, will be temporarily placed for up to 60 hours to treat congestion. The patient will be followed during the hospital stay through discharge and have follow-up assessments at 30-, 60-, 90- and 180-days.

Inclusion Criteria:

1. Age ≥ 18 years

2. Subject is admitted to the hospital with a primary diagnosis of Acute Decompensated Heart Failure (ADHF)

3. Subjects receiving intravenous (IV) diuretic for decompensated heart failure and demonstrating fluid overload. This includes peripheral edema ≥2+ (on a 0 to 4+ scale) and a minimum of 1 of the following:

   • Jugular venous distension ≥10 cm H20;
   • Pulmonary edema as determined by auscultation or imaging;
   • Hepatojugular reflux;
   • Paroxysmal nocturnal dyspnea or ≥ two-pillow orthopnea;
   • Dyspnea at rest with respiration rate ≥20 per minute.

4. Total DAILY diuretic dose prior to admission of ≥80mg Lasix or equivalent

5. Renal function parameters as measured by estimated glomerular filtration rate (eGFR) ≥20 ml/min/1.73m2

6. Subject must meet on one of the following criteria:

   • Subject has had a heart failure hospitalization or worsening of heart failure event requiring IV diuretic therapy (in hospital, emergency room, urgent care, or HF clinic) within the previous 6 months;
   • Renal function as measured by eGFR ≥20 and ≤45 ml/min/1.73m2;
   • At initial HF admission, <600 ml of urine output within 6 hours of initial IV bolus or urine sodium of <50 mmol/L at 1-2 hours after initial IV diuretic dose.

7. Elevated N-Terminal (NT) Pro B-type Natriuretic Peptide (BNP) or BNP:

   • NT Pro BNP >1000 pg/ml (>1500 for subjects with atrial fibrillation);
   • BNP >250 pg/ml (>375 for subjects with atrial fibrillation).

8. Albumin >2.5 g/dL

9. Subject must be able to have device placement procedure within 96 hours of presentation to the hospital and still be demonstrating fluid overload at the time of device placement

10. Subject willing and able to complete study assessments and agrees to comply with all follow-up evaluations

11. Subject has provided written informed consent

Exclusion Criteria:

1. Ultrasound Screening Assessment Exclusion:

   • Subjects' anatomy is not compatible with product dimensions as defined on the eLym system labelling

2. Subjects requiring intravenous vasoactive therapies (e.g., vasodilators, inodilators, inotropes), mechanical ventilation, MCS, or ultrafiltration

3. Subject has experienced a thromboembolic event [e.g., pulmonary embolism (PE), deep vein thrombosis (DVT), transient ischemic attack (TIA), or cerebrovascular events (CVA)] within the previous 6 months

4. Subject has contraindications to systemic anticoagulation

5. Subject currently on Dabigatran

6. Subject with International Normalized Ratio (INR) >2.2 not due to anticoagulation therapy, hypercoagulable state including heparin-induced thrombocytopenia, or on novel anticoagulants (NOACs) that cannot be held for a minimum of 24 hours prior to eLym System placement Note: If subject's INR is >2.2 at the screening and baseline assessment, it may be repeated to assess eligibility up to the time of the procedure.

7. Previous intracranial bleed unless there is documentation that the patient can safely use anticoagulation for 3 days

8. Gastrointestinal (GI) bleeding within 6 months requiring hospitalization and/or transfusion.

9. Recent major surgery within 30 days if the surgical would is judged to be associated with increased risk of bleeding.

10. Platelet count <75 10^3/μL

11. Inability to tolerate anticoagulation therapy for up to 3 days

12. Subject with systolic blood pressure <85 millimeters of mercury (mmHg) at time of enrollment

13. Subject has severe liver disease, liver fibrosis, or hempatorenal syndrome

14. Subject has evidence of active blood stream infection or pneumonia

15. Sustained malignant arrhythmias [e.g., ventricular tachycardia/fibrillation) in the last 90 days]

16. Subject with acute coronary syndrome (ACS) in the last 3 months

17. Subject with severe concomitant disease expected to prolong hospitalization or expected to cause death in ≤ 90 days

18. Subject with a rhythm management device implanted within the last 45 days (i.e., cardioverter/defibrillator, pacemaker, cardiac resynchronization device)

19. Subject is pregnant or lactating. Women of childbearing age who are not post-menopausal or not surgically sterile will need to demonstrate a negative urine or serum test.

20. Physician discretion