Induction of ventricular fibrillation by T wave shock

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Tracing N° 1
Medtronic Devices: ICD Field: Implantation
Patient

A 66-year-old man with valvular heart disease and depressed left ventricular ejection fraction underwent implantation of a dual chamber Virtuoso DR defibrillator for secondary prevention. VF was induced by T wave shock at the end of the procedure.

Graph and trace
  1. Paced events in the atrium and ventricle (AP-VP);
  2. Sequence of ventricular pacing (8 beats - TP) at 150 bpm;
  3. Low energy shock delivered (CD) in the vulnerable period (on the peak of the T wave) of the last paced cycle, at a coupling interval of 310 ms;
  4. Induction of tachycardia in the VF zone (FS) accurately detected by the defibrillator (FD); whilst the capacitors are charging, all ventricular sensed events are labeled VS, even when the rate is inside the VF zone;
  5. Charge end (CE) and 19.8 J charge delivered (CD) by the unit after confirmation of the arrhythmia;
  6. Back-up paced rhythm (AP-VP) and the end of the episode.
Description:

Induced VF, followed by a successful 19.8 J shock requiring a >3 sec charge time; the shock impedance is 47 ohms. These are standard programmed parameters of induction (single detection zone >176 bpm and therapy; ventricular sensing to 1.2 mV).

Comments

VF is induced at the end of procedure to verify:
1) the integrity of the defibrillation circuit and the connection between the leads and the pulse generator;
2) the accurate sensing of VF by the device; a close scrutiny of the tracings is necessary to identify deficiencies in the detection function; 
3) that the VF episode is terminated by a shock delivered by the device; the “defibrillation threshold” is rarely measured, as most operators confirm the presence of a “safe margin” of defibrillation; Note : the tachycardia is not VF, though is treated as such by the ICD, as the rate in inside the programmed VF zone.

Theoritical features / Basic concepts

Implantation Team Facilities in the operating room and patient preparation Implantation procedure Defibrillation threshold testing Post implantation Take Home Messages Implantation Team Different laboratories have different requirements and protocols; in general we recommend the team includes the following members: A doctor trained in implantation of Implantable Cardioverter-Defibrillators (ICD) A cardiac physiologist or technician who is experienced in programming and testing of ICD’s An anesthetist if all or part of the implantation is to be performed under general anesthesia A nurse familiar with the implant suite and laboratory The team must be competent in the management of medical emergencies including cardio-pulmonary resuscitation. Facilities in the operating room and patient...