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Dual-chamber discrimination and dual tachycardia

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Patient

  • 59-year-old man; mitral valve cardiomyopathy with reduced ejection fraction; implanted with a dual-chamber defibrillator

 

Summary

  • episode diagnosed as dual tachycardia by defibrillator with AF and VT
  • A>V but stable rhythm and discordant vectors between tachycardia and the reference vector

 

EGM layout

  1. AF with relatively rapid and irregular atrioventricular conduction
  2. sudden acceleration of ventricular rhythm with change in ventricular electrogram morphology; rhythm becomes regular
  3. at the third consecutive cycle in VT zone, initiation of arrhythmia episode detection; from this interval onwards, each atrial interval is classified as below or above the atrial fibrillation threshold (in this patient, threshold set at 170 beats/minute, nominal value); it is also from this cycle onwards (5 cycles before the episode marker) that stability measurement begins; the mean variance is calculated over these 5 intervals (4 variances)
  4. after 8 consecutive VT cycles, V-Epsd marker
  5. from this cycle, 10 cycles remain until the V-Detect marker is reached; vector correlation analysis is performed over these 10 cycles.
  6. at the end of the duration, diagnosis of dual tachycardia and decision to treat: AF (initially at least 6 out of 10 rapid atrial intervals, then at least 4/10 rapid intervals in a rolling window), stable rhythm (measured variability < programmed stability threshold) without correlation between morphology in tachycardia and reference morphology (for less than 3 beats/10, the vector correlates with the reference vector).
  7. ATP burst (burst of 10 complexes)
  8. probable burst failure and ongoing dual tachycardia
  9. confirmation of persistent tachycardia based solely on a heart rate criteria (V-Detect). No discrimination is applied post-ATP
  10. second burst
  11. effective burst and termination of ventricular arrhythmia

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Take home message

  • this trace shows the value of coupling discriminators for the diagnosis of complex tachycardias such as dual tachycardias; discrimination is performed in stages
  • stage 1, V>A : False
  • stage 2, at least 3 ventricular cycles out of 10 correlated: false (RID-)
  • the analysis continues (step 3) with an analysis of stability and a search for AF
  • the AF rate threshold analysis looks for the presence of a fast atrial rhythm, by comparing the various atrial intervals against a programmed threshold (A Fib rate threshold); the atrial analysis begins when ventricular tachyarrhythmia detection is initialized; each atrial interval is classified as either faster or slower than the A Fib rate threshold; when at least 6 of the last 10 intervals are considered to be faster than the A Fib rate threshold, the device declares that AF is present; this parameter can only be programmed in conjunction with stability
  • stability analysis is performed by measuring the degree of variability in RR intervals during tachycardia; the differences between ventricular cycles, as well as an average difference, are calculated throughout the Duration; when the Duration expires, rhythm stability is assessed by comparing the current average difference with the programmed Stability and “Shock if unstable” thresholds; if the average difference is greater than the programmed thresholds, the rhythm is declared unstable; independent thresholds are available for the Stability (inhibitory) and “ Shock if unstable” functions
  • the idea behind linking the stability and AFib rate threshold criteria is to treat stable rhythms and unstable rhythms without AF (atrial rate < AFib rate threshold), but to inhibit in the presence of an unstable rhythm with atrial rate > AFib frequency threshold (suspicion of conducted AF).
  • in this example, the device finds a diagnosis of AF with a stable rhythm (diagnosis of dual tachycardia) and therapies are delivered

 

This tracing shows a characteristic appearance of dual tachycardia (AF + VT): atrial activity is rapid and polymorphic (cycles correctly classified as AF); the ventricular channel shows abrupt acceleration with a regular, monomorphic tachycardia with a clear change in signal morphology on the shock channel (VT); the device diagnoses double tachycardia (V>A: False, RID-, AF, stable rhythm) and delivers therapies.

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