The purpose of this study is to determine if physiologic pacing will improve symptoms and outcomes in patients with symptomatic first-degree heart block (pr interval ≥250ms).

The purpose of this study is to determine if physiologic pacing will improve symptoms and outcomes in patients with symptomatic first-degree heart block (pr interval ≥250ms). Patient will undergo a comparative effectiveness study where patients with symptomatic first-degree heart block (pr interval ≥250ms) undergo left bundle pacing (3830 lead) and are randomized to DDD-50 vs Managed Ventricular pacing-50 (MVP-50; AAI-DDD 50) and undergo a crossover at 3 months. This study will compare two standard of care options utilizing Food and Drug Administration (FDA) approved devices. Patients are evaluated at baseline, 3 months, and 6 months in terms of patient symptoms, exercise capacity, arrhythmia burden, and patient activity.

Inclusion Criteria:

• Aged 18 or above
• Ventricular Ejection Fraction (EF) > 50%
• New York Heart Association (NYHA) class II-IV
• PR interval ≥250ms
• Narrow QRS duration (≤140ms) or prolonged QRS duration with typical Right Bundle Branch Block (RBBB) morphology on 12 lead ECG and sinus rhythm

Exclusion Criteria:

• Permanent atrial fibrillation (AF)
• Patients who are unable to perform a 6 minute hall walk
• Other serious medical condition with life expectancy of less than 1 year
• Lack of capacity to consent
• Pregnancy
• Contraindication to use of the relevant study device or leads (as per current manuals from manufacturer)