Chapter 3 · Discrimination · Case 7

Dual-chamber discrimination, atrial refractory periods and V>A criterion

Patient and episode

Patient

  • 66-year-old male with severe ischemic cardiomyopathy; implanted with a dual-chamber defibrillator

Summary

  • Initial diagnosis of supraventricular tachycardia based on Rhythm ID with no treatment
  • Subsequent diagnosis of a VT with a series of 5 ATP bursts

The recording

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

Boston Scientific ICD electrogram, segment 1 of 13 — Dual-chamber discrimination, atrial refractory periods and V>A criterion
Boston Scientific ICD electrogram, segment 2 of 13 — Dual-chamber discrimination, atrial refractory periods and V>A criterion
Boston Scientific ICD electrogram, segment 3 of 13 — Dual-chamber discrimination, atrial refractory periods and V>A criterion
Boston Scientific ICD electrogram, segment 4 of 13 — Dual-chamber discrimination, atrial refractory periods and V>A criterion
Boston Scientific ICD electrogram, segment 5 of 13 — Dual-chamber discrimination, atrial refractory periods and V>A criterion
Boston Scientific ICD electrogram, segment 6 of 13 — Dual-chamber discrimination, atrial refractory periods and V>A criterion
Boston Scientific ICD electrogram, segment 7 of 13 — Dual-chamber discrimination, atrial refractory periods and V>A criterion
Boston Scientific ICD electrogram, segment 8 of 13 — Dual-chamber discrimination, atrial refractory periods and V>A criterion
Boston Scientific ICD electrogram, segment 9 of 13 — Dual-chamber discrimination, atrial refractory periods and V>A criterion
Boston Scientific ICD electrogram, segment 10 of 13 — Dual-chamber discrimination, atrial refractory periods and V>A criterion
Boston Scientific ICD electrogram, segment 11 of 13 — Dual-chamber discrimination, atrial refractory periods and V>A criterion
Boston Scientific ICD electrogram, segment 12 of 13 — Dual-chamber discrimination, atrial refractory periods and V>A criterion
Boston Scientific ICD electrogram, segment 13 of 13 — Dual-chamber discrimination, atrial refractory periods and V>A criterion
  1. Probable sinus tachycardia with 1/1 AV relationship; alternating cycles classified as VS and VT-1
  2. Criterion 8/10 met
  3. At the end of the duration, no therapy is delivered; the rhythm is stable and the tachycardia vectors are correlated with the reference vector.
  4. Ongoing cycle-by-cycle analysis
  5. Probable variation in the time at which the R wave is detected by the ventricular lead, explaining the variability of ventricular intervals; rhythm considered unstable; vectors remain correlated, no therapy delivered
  6. Stability criterion met again
  7. Probable atrial extrasystole with some irregularity to the rhythm
  8. New atrial extrasystole; as the PR is relatively long, the atrial extrasystole occurs at the same time as ventricular sensing of the R wave; it falls within the atrial refractory period after ventricular sensing and is not sensed.
  9. Since the atrial extrasystole is not counted, the subsequent compensatory rest is responsible for a false slowing of the atrial rhythm compared to the ventricular rhythm; V>A criterion is satisfied (comparison of atrial and ventricular rate over the previous 10 cycles); this criterion takes precedence over all others; decision to treat
  10. First ATP burst
  11. Continuation of sinus tachycardia
  12. Second ATP burst
  13. Third ATP burst
  14. Fourth ATP burst
  15. Fifth ATP burst
  16. Slowing of sinus rate below VT-1 zone and end of episode

From the interrogation

Interval plots — Dual-chamber discrimination, atrial refractory periods and V>A criterion
Interval plots

Points to remember

  • This episode corresponds to a sinus tachycardia that was initially discriminated correctly; when the vectors are correlated, the device inhibits therapies
  • The device is deceived during a second phase by the non-sensed atrial extrasystole that falls in the refractory period; in fact, the V>A criterion takes precedence over all other criteria, including morphology analysis
  • As a general rule, the V>A criterion enables correct classification of the majority of ventricular tachycardias (atrioventricular dissociation is found in at least 80% of VTs); implementation of this criterion implies good atrial sensing; when the patient has imperfect atrial sensing (small amplitude signals or functional under- sensing, with atrial signals falling in the refractory period), this criterion, which takes precedence over other discriminants (morphology, stability, etc), systematically leads to a diagnosis of VT and must therefore be deprogrammed.
  • For this patient, a first solution could be to avoid overlap between the detection/treatment zones and faster physiological rates
  • Another option is to preferentially use discrimination based on vector analysis, which seems perfectly suited to this patient; this involves deprogramming the V>A criterion responsible for the inappropriate therapies.
On this tracing, we can see that the morphology analysis is in favor of SVT (RID+); an atrial extrasystole falls into the post-ventricular atrial blanking, is not sensed and distorts the atrial rate calculation; the V>A criterion is satisfied and inappropriate therapy is delivered (burst).
On this tracing, we can see that the morphology analysis is in favor of SVT (RID+); an atrial extrasystole falls into the post-ventricular atrial blanking, is not sensed and distorts the atrial rate calculation; the V>A criterion is satisfied and inappropriate therapy is delivered (burst).

Practice out loud

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

00:00

From Boston Scientific ICD — clinical cases by P. Bordachar, M. Strik, A. Thiyagarajah, 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.

Order hardcopyon Amazon