• Dual Chamber Pacemaker
• Mechanism of Pacemaker Tachycardia
• Termination of Pacemaker Tachycardia

Dual Chamber Pacemaker

• Dual Chamber Pacemaker
• Has two electrodes (in the atrium and in the ventricle)
• Pacemaker Tachycardia (PcmT)
• Occurs in a dual chamber pacemaker
• PcmT occurs due to retrograde conduction through the AV node
• The impulse from ventricular pacing
• Travels retrograde to the atria
• and triggers positive sensing in the atria
• Atrial sensing triggers ventricular pacing
• This creates a macro reentry circuit
• Between the atrium and the ventricle
• Similar to antidromic AVRT
  
  
• The most common trigger of PcmT is
• Ventricular extrasystole

Termination of Pacemaker Tachycardia

• Pacemaker tachycardia can be terminated by:
• Slowing retrograde conduction through the AV node
• By administering adenosine (adenosine slows AV node conduction)
• Applying a magnet to the chest over the pacemaker
• A magnet over the pacemaker turns off sensing
• Many pacemakers automatically extend the PVARP during PcmT
• This terminates PcmT because the extended PVARP ignores the sensing of the retrograde P wave
  
  
• As prevention of pacemaker tachycardia:
• The PVARP interval (Post-ventricular atrial refractory period)
• During the PVARP interval, the pacemaker ignores the sensing of the retrograde P wave
• The URL interval (Upper rate limit)
• Is the maximum rate at which the pacemaker can track P waves to the ventricles
• The URL interval defines the maximum rate of pacemaker tachycardia

Pacemaker Tachycardia

• The dual-chamber pacemaker is set to DDD mode (AsVp)
• Heart rate 120/min.
• Stimulation artifacts are only before the QRS complexes
• Retrograde P waves occur outside the PVARP interval
• Sensing retrograde P waves triggers ventricular pacing
• Retrograde P waves are not visible on the ECG
• The tachycardia was terminated by a magnet
• A magnet placed over the pacemaker turns off sensing
• The patient did not have a pacemaker with rate adaptation (DDDR) implanted
• The DDD pacemaker does not adjust pacing rate according to the needs (stress, physical exertion)
• And a rate of 120/min is not physiological