Tachycardia due to electronic re-entry

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Tracing N° 10
Boston Scientific Devices: CRT Field: Management of atrial arrhythmias
Patient

Patient 1 : A 71-year old male patient implanted with a triple-chamber Boston Scientific Autogen CRT-D revealed an episode of PMT during interrogation of the device.

Patient 2 : 69-year old male patient implanted with a triple-chamber Boston Scientific Autogen CRT-D revealed an episode of PMT during interrogation of the device.

Graph and trace

Patient 1 :

  1. atrial sensing and biventricular stimulation.
  2. premature atrial contraction with early biventricular stimulation.
  3. retrograde conduction and tachycardia by electronic re-entry at the maximal tracking rate with prolongation of the AV delay.
  4. diagnosis of PMT after 16 consecutive cycles (atrial sensing, biventricular stimulation at the maximal tracking rate with stable VP – AS intervals).
  5. prolongation of the PVARP during one cycle.
  6. termination of the PMT.

Patient 2 :

  1. atrial sensing and biventricular stimulation.
  2. non-sustained VT with retrograde conduction.
  3. retrograde conduction with tachycardia by electric re-entry at the maximal tracking rate.
  4. diagnosis of PMT is made after 16 consecutive cycle (atrial sensing, biventricular stimulation at the maximal tracking rate with stable VP – AS intervals).
  5. prolongation of the PVARP during one cycle.
  6. interruption of the PMT.
Comments

These tracings correspond to two episodes of PMT induced by premature atrial contraction (A) or non-sustained VT (B). For a Boston Scientific device, the diagnosis of a PMT is made after the occurrence of 16 consecutive AS – VP cycles at the maximal tracking rate. The VA intervals are required to be stable; when one of the 16 VA intervals varies by more than 32 ms from the first VA interval of the tachycardia, the intervals are considered unstable and the counter (fixed at 16 consecutive cycles) is reset at zero. When the device diagnoses PMT, the PVARP is prolongated to 500 ms for one single cycle (corresponding to the 16th cycle).

Atrial or ventricular extrasystoles, isolated or in bursts, are major contributors for induction of PMTs since they cause an offset between ventricular and atrial depolarization. To avoid these types of episodes, the most suitable solution is probably to extend the PVARP so that it exceeds the retrograde conduction delay.