Dual chamber discrimination, threshold for correlation

Tracing
N° 11
Manufacturer Boston Scientific Device ICD Field Discrimination
Patient

This 58-year-old woman underwent implantation of an Incepta single chamber defibrillator. 
Graph and trace
  1. sinus tachycardia;
     
  2. acceleration in the slow VT-1 zone (520 ms);
     
  3. after 3 cycles classified VT-1, analysis of the correlation;
     
  4. 8 out of 10 criterion fulfilled;
    at the end of Duration, diagnosis of SVT based on high correlation between morphology during tachycardia and morphology of reference EGM; therapy withheld;
     
  5. continuation of cycle-by-cycle analysis;
     
  6. on this cycle, the criterion of correlation was no longer fulfilled. The analysis reveals <3 out of 10 cycles with >94% correlation (a programmable threshold with this type of device), despite minimal variations in the EGM morphology on the high-voltage channel. The decision to treat was made ;

 

  1. burst of ATP;
     
  2. persistence of sinus tachycardia; during redetection, no discrimination (no analysis of the level of correlation);
     
  3. second burst of ATP;
     
  4. third burst of ATP;
     
  5. the ventricular rate slows slightly and falls below the VT zone;
Comments

This episode highlights the importance of the possibility of programming the threshold for correlation. This episode of sinus tachycardia is initially appropriately diagnosed as a supra-ventricular tachycardia. However, the percentage of correlation hoovers around the programmed threshold of 94%. During a certain number of cycles, a majority of the measurements are 93% (below the threshold) explaining the occurrence of inappropriate therapies. The threshold was therefore modified to a lower value solving the problem. 

Message to remember

Inhibition initially based on Rhythm ID, before diagnosis of VT and delivery of 3 bursts of 

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