Pacemaker therapy has been recognized as effective for the control of sinus and atrio-ventricular (AV) node dysfunction. Single chamber pacing when compared with dual chamber pacing, has numerous advantages of low complication rates, lower cost, better longevity, with non-inferiority in the quality of life and hard outcomes proven in direct randomized comparisons. However, comparison between single and dual chamber pacers was never adequate, since not more then half of the patients in the trials were actually using pacemakers for the majority of the time. Routine dual chamber pacing using a right ventricle apical lead is also associated with significant increase in peri-operative and remote complications. Some of these complications may be related to ventricular desynchronization secondary to the pacing location, which is potentially avoidable by using biventricular pacing. A randomized trial which will compare single chamber rate responsive pacing to the best available modification of dual chamber pacing (biventricular pacing) in suitable patients is therefore warranted.

Inclusion Criteria:

• Patient has symptomatic bradycardia and is a candidate for first pacemaker implantation

• Patient has high risk of being pacemaker dependent by (at least one of the following):

  1. Average heart rate of 60 or less on pre-implant Holter
  2. Maximal heart rate of 60 in patient on telemetry monitoring 12 hrs preoperatively, when not under medications decreasing heart rate, or under chronic medical treatment inducing bradycardia, which is unlikely to be changed
  3. First degree AV block with PR intervals > 300 ms, or second degree AV block at heart rates <= 80 bpm.
  4. Dependence for 12 hrs when on temporary pacemaker set at 50 bpm if bradycardia is not secondary to medication, or under chronic medical treatment inducing bradycardia, which is unlikely to be changed.

Exclusion Criteria:

• Age <= 65 years
• Chronic Atrial Fibrillation
• Indication for ICD
• Non-cardiovascular death is likely to occur within 3 years
• Geographical, social, or psychiatric reasons making follow-up problematic