The LEADLESS Observational Study

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…