Shock in the VT zone

N° 17
Manufacturer Medtronic Device ICD Field Therapy

Patient implanted with dual-chamber ICD (Entrust DR) for ischemic cardiomyopathy; consultation for electrical shock.

Graph and trace

The graph shows a probable ventricular arrhythmia detected in the VT zone, treated successively with 6 sequences of anti-tachycardia pacing (3 bursts followed by 3 ramps) which do not allow the return to sinus rhythm followed by an electrical shock of 10 Joules with successful termination.

  1. the EGM confirms ventricular tachycardia with atrioventricular dissociation;
  2. 3 successive bursts (fixed rate) which prove ineffective;
  3. 3 ramps (increment between each stimulus);
  4. the ensuing therapy is an electrical shock;
  5.  after a very short charge time, an electrical shock of 10 Joules is delivered;
  6. successful shock and termination of the arrhythmia.

In the absence of an optimal universal programming, the results of large-scale studies concur on the need to limit the incidence of inappropriate or unnecessary therapies without jeopardizing patient safety and to prioritize anti-tachycardia pacing in lieu of electrical shocks. It is customary to program increasingly aggressive therapies and anti-tachycardia pacing represents the first-line treatment for monomorphic tachycardia. In the VT zone (<200 beats/minute), a series of bursts rather than ramps (Class I indication) is therefore usually programmed. Indeed, the ratio between termination and acceleration of the arrhythmia appears to favor burst therapy (identical efficacy but less prominent pro-arrhythmogenic feature) compared to the ramp. If the bursts prove unsuccessful, it is then possible to program a series of ramps to promote a painless therapy and subsequently a series of electrical shocks. In this example, a shock of 10 Joules allows terminating the arrhythmia and the return to sinus rhythm. Various parameters influence the choice of the amplitude of the first shock in the VT zone, which can be programmed at maximum energy or at a lower amplitude (in the order of 10 Joules). A certain number of advantages can be found in programming a first shock of moderate amplitude (10 Joules):

  1. this amplitude is very often sufficient to terminate a VT episode;
  2. the charge time for this amplitude is very short, even though the few seconds difference from a maximum amplitude are not clinically determinant when the shock occurs after 3 burst sequences plus or minus 3 ramp sequences (more than one minute of arrhythmia);
  3. battery consumption is less for a shock at 10 Joules versus 35 Joules despite having little impact on the wear of the batteries if the number of shocks delivered is limited;
  4. despite the fact that while most of the time during a VT episode, the electrical shock is delivered while the patient is still conscious, the painful nature of the treatment has little bearing on the decision regarding the amplitude of the first shock, given the difficulty in demonstrating a direct link between the amplitude of the shock delivered and the amplitude of the pain incurred;
  5. various studies have demonstrated the deleterious nature of an electrical shock and its association with an altered prognosis; it therefore appears reasonable to assume that a shock of 10 Joules will have fewer negative consequences than a shock of 35 Joules and would hence seem desirable to choose the least traumatic therapy possible.