Physiologic Pacing for Symptomatic First-Degree Heart Block

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)