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ATP burst in the VF zone with acceleration - Incepta CRT

Patient

  • 83-year-old male with severe cardiomyopathy and permanent AF; implanted with an Incepta triple-chamber defibrillator

 

Summary

  • episode classified in the VF zone
  • ATP in the VF zone and 31 Joule shock

 

EGM layout

  1. Monomorphic VT detected in the VF zone
  2. initial detection satisfied for VF zone (8 cycles out of 10 in FV zone); start of initial VF zone duration (1 second)
  3. detection of a VF episode (V-Detect); ventricular rate measured over the 4 cycles preceding the V-Detect marker is below 250 beats/minute (226 bpm)
  4. ATP Quick Convert: burst of 8 stimuli at a fixed rate (identical coupling between the last sensed cycle and the first paced cycle, then between the different paced impulses).
  5. the first ventricular cycle is sensed in the refractory period following anti-tachycardia pacing (in square brackets); the second is not counted (–)
  6. the device analyzes the effectiveness of the pacing sequence: the first 2 cycles following the cycle that was no counted are considered fast (VF-VF); the 2 cycles/3 fast criterion is therefore met and capacitor charging begins (Chrg); when the burst has been ineffective, the start-of-charging marker appears on the trace 300 ms after charging has actually begun; charging begins on the second fast cycle, but the marker may not be visible until the third.
  7. accelerated arrhythmia with rapid, low-voltage ventricular cycles
  8. end of charge, 500 ms diversion window; shock on second fast cycle
  9. effective shock and arrhythmia termination


Take home message

  • ATP Quick Convert is the anti-tachycardia pacing sequence that can be delivered in the VF zone of a Boston Scientific defibrillator; it is ATP before charge.
  • ATP before charging reduces energy consumption; once VF has been diagnosed, ATP is delivered; if VF is reconfirmed after ATP has occurred, capacitor charging begins; if arrhythmia terminates, charging is not initiated; this saves capacitor charging if ATP is effective; on the other hand, if ATP is ineffective, it delays shock delivery by 2 to 3 seconds
  • this pacing sequence can only be delivered following initial detection in the VF zone, if the tachycardia sequence does not exceed 250 or 300 beats/minute (programmable on the latest platforms).
  • the characteristics of this anti-tachycardia pacing sequence are not programmable: it is a burst of 8 stimuli with an 88% coupling interval
  • following this sequence, the device evaluates the effectiveness of the therapy; if at least 2 out of 3 cycles are considered slow, charging is cancelled; conversely, if at least 2 out of 3 cycles are considered fast, charging of the capacitors begins.
  • in this example, ATP is not only ineffective but also accelerates tachycardia; a real-life study carried out on Boston Scientific defibrillators showed that, while the effectiveness of a first-line shock for an episode of VF averaged 90%, this success rate fell when the shock was delivered after an anti-tachycardia pacing sequence; one explanation lies in the risk of acceleration, as in this example, from a monomorphic arrhythmia to a very rapid polymorphic arrhythmia, with an increased risk of an ineffective shock; if ineffectiveness or a pro-arrhythmic effect is observed, it is advisable to deprogram the anti-tachycardia pacing sequence

 

Characteristics of anti-tachycardia pacing in the VF zone: the tachycardia frequency limit up to which ATP will be applied is programmable at either 250 or 300 beats/minute; other parameters are not modifiable (1 burst, 88% coupling, 8 stimuli).

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