Counters and therapies in the VT zone

Tracing N° 1
Abbott Devices: ICD Field: Securesence

This 67-year-old man received a St. Jude Medical Ellipse™ VR defibrillator for the management of advanced ischemic cardiomyopathy complicated by repetitive episodes of non-sustained (NS) VT. He was seen for evaluation of syncope and delivery of an electric shock. 

Graph and trace

Tracing 1A

  1. sinus rhythm; cycles classified VS;
  2. sudden onset of a regular monomorphous tachycardia, with change in morphology; probable VT; initial cycles classified (-) because of discordance between the instantaneous (fast) and average of the 4 previous cycles (slow);
  3. first cycle classified T (concordance between instantaneous and averaged cycles);
  4. after 6 T classified cycles, episode recorded in the electrogram (EGM) memories (NSVT);
  5. spontaneous termination after 7 T classified cycles; the VT counter was not filled;

Tracing 1B

  1. similar episode;
  2. spontaneous termination after 13 T classified cycles (a few cycles before filling of the VT counter);

Tracing 1C

  1. similar episode;
  2. after 16 T classified cycles, the VT counter is filled;
  3. first therapy corresponding to the VT zone; it is a ramp;
  4. subtle acceleration of the ventricular rate followed by termination;

Tracing 1D

  1. similar episode;
  2. after 16 T classified cycles, the VT counter is full;
  3. 3: first therapy corresponding to the VT zone; it is a ramp (pacing with cycles shortening from 252 to 200 ms);
  4. instead of termination, the ventricular rhythm is markedly accelerated, detected in the VF zone and becomes polymorphous;
  5. after 12 F classified cycles, an episode of VF is detected; the capacitors begin to charge;
  6. end of charge and delivery of 30 J shock;
  7. end of arrhythmia and return to sinus rhythm diagnosed;

These tracings highlight 2 critical points of ICD programming:

- This patient had undergone device implantation in the context of ischemic cardiomyopathy with multiple episodes of asymptomatic or nearly asymptomatic NSVT (4 to 20 cycles). He never experienced an episode of sustained VT or of syncope before the implantation. Not long thereafter, he presented after loss of consciousness and electric shock in absence of apparent triggering factor. Interrogation of the memories revealed many episodes of NSVT, as well as a few episodes treated by ATP and a single episode treated by a shock. Further scrutiny of the tracing revealed a proarrhythmic effect of the ramp and acceleration of stable VT to a rapid, polymorphous ventricular arrhythmia causing syncope and terminated by a life-saving electric shock. It seems highly likely that this episode was due to a poorly chosen programming. The priority in the management of these episodes of NSVT was to promote their spontaneous termination, and to program a sufficient number of cycles to avoid this undesirable outcome. Acceleration of an arrhythmia is an immediate risk, should its treatment with a shock be unsuccessful, as well as prognostically unfavorable on the long-term, since the survival of patients is jeopardized by the delivery of multiple electric shocks. The device programming was, therefore, modified by an increase in the number of cycles needed to fill the counters, from 16 to 30 in the VT, and from 12 to 30 in the VF zones. This should offer a wide enough margin and promote a spontaneous termination without increasing significantly the risk of syncope, should the tachyarrhythmia be sustained, keeping in mind that, in the updated professional guidelines, it is now a class I indication. 

- These tracings underscore another important point with regard to the choice of programming of the type of ATP sequence. The first therapy in the VT zone was a ramp, which may be surprising and against the latest guidelines, which clearly favor the programming of bursts (recommendation class I level), apparently more effective from the standpoint of the terminations / accelerations ratio. Furthermore, the coupling and the decrement of that ramp were probably both excessively aggressive, since the last pulse was delivered at the shortest coupling interval of 200 ms. The programming was replaced by 3 bursts, followed by the highest amplitude shocks in the VT zone.