The objective of the study is to confirm clinical performance and safety of the Nanostim leadless cardiac pacemaker system within its intended use and according to its instructions for use.

Inclusion Criteria:

• Subject must have one of the following clinical indications: Chronic atrial fibrillation with 2 or 3° AV or bifascicular bundle branch block (BBB block) ; or Normal sinus rhythm with 2º or 3° AV or BBB block and a low level of physical activity or short expected lifespan (but at least one year); or Sinus bradycardia with infrequent pauses or unexplained syncope with EP findings; and
• Subject ≥18 years of age; and
• Subject has life expectancy of at least one year and is a suitable candidate based on overall health and well-being; and
• Subject is not enrolled in another clinical investigation with a treatment arm or that could confound the results of this study; and
• Subject is willing to comply with clinical investigation procedures and agrees to return for all required follow-up visits, tests, and exams; and
• Subject has been informed of the nature of the study, agrees to its provisions and has provided written informed consent, approved by the EC; and
• Subject is not pregnant and does not plan on getting pregnant during the course of the study.

Exclusion Criteria:

• Known pacemaker syndrome, have retrograde VA conduction or suffer a drop in arterial blood pressure with the onset of ventricular pacing; or
• Hypersensitivity to < 1 mg of dexamethasone sodium phosphate; or
• Mechanical tricuspid valve prosthesis; or
• Pre-existing pulmonary arterial (PA) hypertension (PA systolic pressure exceeds 40mmHg or RV systolic pressure (RVSP) as estimated by echo exceeds 40mmHg) or significant physiologically-impairing lung disease (has severe pulmonary disease producing frequent hospitalization for respiratory distress or requiring continuous home oxygen); or
• Pre-existing ventricular pacing or defibrillation leads; or
• Current implantation of either conventional or subcutaneous implantable cardioverter defibrillator (ICD) or cardiac resynchronization therapy (CRT); or
• Presence of implanted vena cava filter; or
• Evidence of thrombosis in one of the veins used for access during the procedure; or
• Cardiovascular or peripheral vascular surgery/intervention within 30 days of enrolment; or
• Presence of implanted leadless cardiac pacemaker

Subjects who are at least 18 years old and who are indicated for a VVI(R) pacemaker