ASCEND CSP IDE Study

Inclusion Criteria:

1. Subject must meet current clinical practice guidelines for implantation of ICD orCRT-D and will undergo one of the following:

2. de novo Abbott ICD system implant (single or dual chamber)

3. de novo Abbott CRT-D system implant and is intended to also undergo leftventricle coronary sinus lead implant (for patients indicated for CRT-Daccording to locally approved indications)

4. Subject is ≥ 18 years of age or age of legal consent, whichever age is greater.

5. Subject is willing to undergo implant defibrillation testing if requested. Subjectswith AF in whom defibrillation testing is required must have been on or willing tobe on uninterrupted anticoagulation therapy before, during, and after the implantprocedure.

6. Subject is willing to comply with clinical investigation procedures and agrees toreturn to clinic for all required follow-up visits, tests, and exams.

7. Subject has been informed of the nature of the clinical investigation, agrees to itsprovisions and has provided a signed written informed consent, approved by theIRB/EC.

Exclusion Criteria:

1. Subject has had myocardial infarction or unstable angina within 40 days prior tosigning consent

2. Subject has had recent cardiac revascularization (angioplasty, stent or bypassgraft) in the 4 weeks prior to signing consent or planned within 3 months followingconsent

3. Subject has had any other therapeutic cardiovascular procedure (such astranscatheter aortic valve replacement, MitraClip, cardiac surgery, left atrialappendage closure, patent foramen ovale closure, or any ablation procedures) in the 3 months prior to signing consent or planned within 3 months following consent

4. Subject has had a recent Cerebrovascular Accident (CVA) or Transient Ischemic Attack (TIA) within 3 months of prior to signing consent

5. Subject has a life expectancy of less than 12 months

6. Subject has contraindications for standard RV transvenous and/or LBBAP leadplacement (e.g., mechanical right heart valve)

7. Subject is contraindicated for ≤1mg Dexamethasone sodium phosphate.

8. Subject is pregnant or breastfeeding women, or women of childbearing potential andwho are not on a reliable form of birth regulation method or abstinence

9. Subject has an existing pacemaker (including a temporary pacing system), ICD, CRT,or cardiac contractility modulation (CCM) device or leads

10. Subject has any evidence of active infection or undergoing treatment for aninfection

11. Subject is enrolled or planning to enroll in another clinical trial that mightconfound the results of the present study

12. Subject has moderate or severe aortic stenosis

13. Subject has ventricular septal defect (VSD) or had prior surgery on theinterventricular septum that could impact LBBAP implant, such as septal myomectomy,ethanol septal ablation, VSD repair, etc

14. Subject has end-stage renal disease

15. Subject has NYHA IV classification

16. Subject has undergone cardiac transplantation or have a classification of Status 1for cardiac transplantation or consideration for transplantation during the studyfollow-up period

17. Subject has had previously extracted leads

18. Subject has had an LV Assist Device

19. Subject has had a failed LBBAP lead implant

Defibrillation testing exclusion criteria (these are part of general exclusion criteria when defibrillation testing is requested):

1. Subject has pre-existing or suspected pneumothorax during implant

2. Subject has current known intracardiac left atrial or Left Ventricular thrombus

3. Subject has severe proximal three-vessel or left main coronary artery diseasewithout revascularization

4. Subject has Ejection Fraction less than 20%

5. Subject has recent stroke or transient ischemic attack (within the last 6 months)

6. Subject has known inadequate external defibrillation

7. Subject has any other known medical condition not listed that precludes theirparticipation in the opinion of the investigator