Burst of ATP during the capacitors charge in the VF zone

Tracing
N° 39
Manufacturer Abbott Device ICD Field Therapy
Patient

This 57-year-old man presenting with ischemic cardiomyopathy and episodes of sustained VT complicated by syncope received a Fortify single chamber ICD. He was seen in consultation after he experienced electrical shocks.

Graph and trace

Episode of VF with ATP delivered during the capacitors charge and cancelled electrical shock.

Tracing

  1. VES;
  2. Fast tachycardia detected in the VF zone; diagnosis of VF after 12 F cycles;
  3. Onset of the capacitors charge and simultaneous delivery of a salvo of 8 ATP cycles at a fixed rate;
  4. Termination of the arrhythmia;
  5. Diagnosis of return of sinus rhythm (after 5 VS cycles without intervening T or F cycles) and interruption of the capacitors charge (5 sec after its onset).

Narrative

New VF episode with ATP during the charge, followed by 36-J shock.

Tracing

  1. New arrhythmic episode, similar to the previous one;
  2. Burst during the charge + capacitors charge;
  3. Failure of the salvo, continuation of the arrhythmia and of the charge of the capacitors;
  4. At the end of the charge, confirmation of the tachycardia and delivery of 36-J shock;
  5. Termination of the tachycardia and diagnosis of return of sinus rhythm.

Narrative

New VF episode with delivery of ATP followed by 36-J shock.

Tracing

  1. New arrhythmic episode, similar to the previous one;
  2. Burst during the charge + capacitors charge;
  3. Termination of the arrhythmia; however, the number of VS was insufficient to fill the counter of sinus rhythm restoration (only 3 VS cycles instead of 5 needed); continuation of the capacitors charge;
  4. Early recurrence of the arrhythmia;
  5. Electrical shock at the end of charge;
  6. Interruption of the arrhythmia and diagnosis of return of sinus rhythm.
Comments

A priority objective of ICD programming is to minimize the risk of electrical shock delivery, while preserving the patient’s safety. A large proportion of fast tachycardias diagnosed in the VF zone are organized, monomorphic, and amenable to ATP therapy. Pacing during the charge of the capacitors can be, therefore, offered to lower the likelihood of electrical shocks. The diagnosis of VF triggers the charge of the capacitors and the ATP sequence simultaneously. The shock is not delivered if ATP is successful. In this patient, a clear advantage consisted in the termination of the tachycardia without shock delivery, a key ingredient of his quality of life. On the other hand, the charge of the capacitors consumes energy, which might be problematic if repetitive. However, the shock was diverted, preventing a full charge, and sparing some battery life. Had ATP been unsuccessful, the charge would have continued uninterrupted, and the shock would not have been delayed by ATP. On the last tracing, the salvo of ATP was successful, though the tachycardia recurred before the diagnosis of restoration of sinus rhythm and the shock was delivered at the end of the charge.

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