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VF episode correctly detected and treated with maximum output shock - Resonate CRT

Patient

  • 57-year-old male with ischemic cardiomyopathy; implanted with a Resonate triple-chamber defibrillator

 

Summary

  • episode classified in the VF zone
  • 41 Joule shock with a charge time of approximately 9 seconds
  • shock impedance of 54 Ohms

 

EGM layout

  1. sinus rhythm and biventricular pacing (AS, RVP-LVP)
  2. spontaneous, very rapid, polymorphic ventricular arrhythmia; first cycle classified as VT, subsequent cycles as VF
  3. V-Epsd marker (criterion 8/10 met); criterion fulfilled for VT zone (1 cycle in VT zone + 7 cycles in VF zone); initial detection duration for the VT zone starts on this beat
  4. on this cycle, the initial detection window is satisfied for the VF zone (8 cycles in the VF zone); the initial detection duration for the VF zone begins on this beat; the VF zone duration takes precedence over the VT zone duration; even if the VT zone duration ends before the VF zone duration, if the 6/10 criterion is satisfied for the VF zone, VT zone therapies are suspended until the VF zone duration ends.
  5. persistence of arrhythmia in the VF zone for the initial duration of 5 seconds in the VF zone (V-Detect)
  6. start of capacitor charging
  7. ventricular sensing remains adequate during charging, with the exception of a few under-sensed cycles which explain the RVS markers; these undersensed events are too far apart to cause charge diversion.
  8. end of charge; the charge lasted approximately 9 seconds, with the amplitude of the shock delivered corresponding to the maximum capacity of the device
  9. a refractory period of 135 ms begins at the end of the charge; the first cycle following this refractory period is not counted (–); the 2 following cycles are fast (VF), the charge diversion window has elapsed (500 ms after the end of the charge); criterion 2/3 met.
  10. 41 Joule shock delivered on the second cycle (synchronized with the R wave)
  11. the first atrial cycle following the post-shock refractory period (500 ms) is not counted (–)
  12. in the absence of spontaneous ventricular activity, ventricular pacing occurs 2 seconds after the shock
  13. effective shock and arrhythmia termination

Take home message

  • implantable defibrillators were historically developed to prevent the risk of sudden death and terminate malignant ventricular arrhythmia via a shock
  • this tracing illustrates normal defibrillator operation during a VF episode: correct arrhythmia detection, capacitor charging, confirmation at the end of charge and effective shock
  • the arrhythmia is immediately extremely rapid, polymorphic and disorganized, consistent with VF; any attempt to terminate this type of arrhythmia by anti-tachycardia pacing is doomed to fail, and a shock remains the standard therapy in this setting
  • detection is correct and there is no discrimination of arrhythmia origin in this ventricular rate range
  • for a Boston Scientific defibrillator, a series of 8 shocks can be programmed in the VF zone
  • the amplitude of shocks 3 to 8 is not programmable and is always the maximum (41 Joules)
  • the amplitude of the first 2 shocks is programmable, even though the amplitude of the second shock must be at least equal to that of the first; the amplitude of the second shock is generally programmed at the device’s maximum capacity
  • the amplitude of the first shock can either be programmed to the maximum capacity of the device, or to a lower value of 10 to 20 Joules; programming a first shock of intermediate amplitude makes it possible to reduce the charge time and the delay between arrhythmia onset and shock delivery, and may in certain specific cases reduce the risk of loss of consciousness; the choice of the amplitude of the first shock in the VF zone therefore represents a compromise: medium energy may be enough to terminate VF after a short charge time, but if this fails, the second, maximum-energy shock is delivered after a long total duration in VF; maximum energy is more effective from the outset, but at the cost of a longer initial charge time
  • international recommendations state that it is reasonable (class IIA recommendation) to program the maximum amplitude in VF zones from the outset, unless an induction test has shown efficacy at a lower amplitude.

 

This figure shows the various programming options for the amplitude of the first shock in the VF zone; the amplitude of the second shock is also programmable but must be at least equal to that of the first; the amplitude of shocks 3-8 is necessarily maximum (41 joules; in the VF zone, 8 shocks can be delivered).

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