Chapter 1 · Counters · Case 7

No confirmation for a second shock

Patient and episode

Patient

  • Male implanted with a single-chamber defibrillator (Visia AF XT VR) for ischaemic cardiomyopathy.

The recording

Tap a number on the trace, or an entry in the list below

Rate / interval plot

Medtronic ICD electrogram, segment 1 of 1 — No confirmation for a second shock

EGM

Medtronic ICD electrogram, segment 1 of 2 — No confirmation for a second shock
Medtronic ICD electrogram, segment 2 of 2 — No confirmation for a second shock
  1. What diagnosis are you suggesting on this graph? The plot shows a sudden acceleration of the ventricular rhythm with rapid cycles detected in the VF zone; a burst and then a shock are delivered; the first shock seems ineffective with persistence of the arrhythmia which terminates in a second phase; a second shock is delivered just as the rate seems to have normalised.
  2. What is your diagnosis? The tracing shows a rapid, monomorphic ventricular arrhythmia detected in the VF zone.
  3. What therapy is delivered? This is a burst before the charge.
  4. What therapy is delivered? This is a burst during the charge, the first burst having been ineffective.
  5. What therapy is delivered? This is a maximum output shock delivered when the 2 bursts have proved ineffective.
  6. What is the effect of the shock? The shock was ineffective and a monomorphic ventricular arrhythmia persisted; the redetection counter was filleded (12/16).
  7. How do you explain the delivery of this second shock? The ventricular arrhythmia has spontaneously terminated during charging; once the re-detection counter was filled, therapy (second shock) cannot be abandoned; at the end of charging, the device synchronises with the first ventricular complex detected and the shock is delivered.

Points to remember

  • In the VF zone, the defibrillator operates differently between the first shock in a series and any subsequent shocks (shocks 2 to 6).
  • For the first shock, charging can be interrupted or abandoned; following initial detection, charging can be interrupted if the arrhythmia terminates spontaneously during charging (evidence of at least 4 slow cycles out of 5); similarly, if the arrhythmia terminates spontaneously at the end of charging, the charge can be abandoned (evidence of at least 4 slow cycles out of 5 after the CE marker).
  • Conversely, for shocks 2 to 6, when the redetection counter is filled, charging can no longer be interrupted or abandoned and the shock will be systematically delivered, with an attempt to synchronise to a ventricular sensed event at the end of the charge; in fact, if the redetection counter was filled, the device considers that the shock was ineffective and starts charging the capacitors; if it diagnoses reversion when charging has begun, the shock is still delivered at the end of charging ; this is to avoid withholding essential therapy in the event of under-sensing that can result in an incorrect diagnosis of arrhythmia termination.

Practice out loud

Just describe the tracing. What do you think is going on? Describing the numbers can help.

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From Medtronic ICD — clinical cases by P. Bordachar, A. Thiyagarajah, L. Fontagne, M. Strik, S. Ploux. Published by Cardiocases. Every numbered marker on a recording is explained in the list beneath it; tap a marker on the trace or an entry in the list.

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