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Dual-chamber discrimination and AF with aberrant conduction

Patient

  • 65-year-old male with severe ischemic cardiomyopathy; implanted with a dual-chamber defibrillator for primary prevention.

 

Summary

  • episode diagnosed in the VT zone
  • A>V and rhythm ID discrimination

 

EGM layout

  1. rapid atrial activity (probable atrial tachycardia) with rapid and variable atrio-ventricular conduction with alternating VS, VT then VF cycles
  2. criterion 8/10 met (V-Epsd)
  3. at the end of the duration, decision not to treat in the presence of AF (atrial rate > A Fib rate threshold), unstable ventricular rhythm (stability value > programmed threshold of 30 ms) with absence of correlation between tachycardia vectors and reference vector (less than 3 cycles/10 correlated; note that cycles classified as VF are systematically considered uncorrelated); electrogram analysis shows variability in the appearance of ventricular electrograms on the shock channel, with widening on the shortest cycles
  4. continuation of cycle-by-cycle analysis with no change in diagnosis (aberrantly conducted AF)

Take home message

  • dual tachycardias and AF with aberrant conduction are probably the most difficult tachycardias to discriminate for a dual-chamber defibrillator; in fact, the V>A criterion does not allow a decision to be made, since in both cases the atrial rhythm is faster than the ventricular rhythm; in both cases, there is also no correlation between the vectors during tachycardia and the reference vector.
  • when morphology analysis is combined with stability and the search for AF, stability determines the diagnosis when the vectors are not correlated and the atrial rate > A Fib rate threshold: if the rhythm is stable, the device diagnoses dual tachycardia and delivers therapies; if the rhythm is unstable, it diagnoses AF with aberrant conduction and inhibits therapies (as in this example)

This tracing shows a characteristic appearance of atrial tachycardia with aberrant conduction: atrial activity is rapid and regular (cycles correctly classified as AF); the ventricular channel shows an irregular rhythm with a variable appearance of QRS complexes on the shock channel (narrow QRS on long cycles, wide QRS on rapid cycles); the device diagnoses AF with aberrant conduction (V>A: False, RID-, AF, unstable rhythm) and inhibits therapies.

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