Chapter 4 · Keeping up the CRT · Case 10

Sinus tachycardia, Wenckebach and pro-arrhythmia

Patient and episode

Patient

  • COGNIS CRT-D in a 61-year-old man with ischaemic cardiomyopathy and left bundle branch block
  • Seen after a shock felt during exertion at night

The recording

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

Boston Scientific CRT electrogram, segment 1/8 — Sinus tachycardia, Wenckebach and pro-arrhythmia
Boston Scientific CRT electrogram, segment 2/8 — Sinus tachycardia, Wenckebach and pro-arrhythmia
Boston Scientific CRT electrogram, segment 3/8 — Sinus tachycardia, Wenckebach and pro-arrhythmia
Boston Scientific CRT electrogram, segment 4/8 — Sinus tachycardia, Wenckebach and pro-arrhythmia
Boston Scientific CRT electrogram, segment 5/8 — Sinus tachycardia, Wenckebach and pro-arrhythmia
Boston Scientific CRT electrogram, segment 6/8 — Sinus tachycardia, Wenckebach and pro-arrhythmia
Boston Scientific CRT electrogram, segment 7/8 — Sinus tachycardia, Wenckebach and pro-arrhythmia
Boston Scientific CRT electrogram, segment 8/8 — Sinus tachycardia, Wenckebach and pro-arrhythmia
  1. First stored episode, diagnosed as PMT (A 121, V 120 bpm). Each atrial event is sensed (AS 490 to 503 ms) and both ventricles are paced at the maximum tracking rate: LVP-MT and RVP-MT at 500 ms (120 bpm)
  2. After 16 consecutive AS – BiV cycles at the maximum rate, with a stable BiV-AS interval, the device diagnoses a PMT (PMT-B)
  3. The PVARP is extended to 500 ms for one cycle: the next atrial event falls in it ((AS) 503) and starts no AV delay
  4. Pacing resumes at the sensor rate: AP-Sr 403 ms after the untracked atrial event, then RVP-Sr and LVP-Sr at 838 ms. But this is a conducted beat (its RV EGM differs from the paced beats): BiV pacing is lost on this beat
  5. The sinus tachycardia goes on and is tracked again (AS 590, RVP and LVP at 590 ms), then BiV pacing at the maximum tracking rate again (500 ms)
  6. Same sequence 16 VP-MT cycles later: PMT-B, and a new atrial event not tracked ((AS) 493)
  7. Same sequence again: PMT-B, (AS) 500 not tracked, AP 393, then RVP and LVP at 855 ms on a conducted beat (different RV EGM: BiV pacing lost on that beat), then back to BiV pacing at the MTR. BiV pacing is thus lost on one beat after every run of 16 VP-MT cycles
  8. Second stored episode, 14 minutes later (VT, A 125, V 234 bpm). The sinus rate exceeds the MTR (AS 470 to 483 ms, against 500 ms for the VP-MT): the AV delay lengthens beat after beat, then an atrial event falls in the PVARP ((AS) 480): Wenckebach behaviour
  9. That atrial event starts no AV delay and no ventricular pace: a long cycle (AP-Sr, then RVP-Sr and LVP-Sr at 750 ms). A fast VT starts just after (cycles of 235 to 295 ms), detected in the VF zone (VF markers, V-Epsd)
  10. V-Detect in the VF zone: Quick Convert, ATP before charging in the VF zone, a burst of 8 BiV pulses (RVP, LVP 0) at 230 ms
  11. The burst fails: the VT goes on (VT 288, then VF 265 ms) and the capacitors charge (Chrg). A shock is delivered at the end of charging (not shown on this tracing) and stops the VT; episode report: 41 J shock, charge 9.5 s, lead impedance 38 Ω

Points to remember

  • At the MTR, an exercise sinus tachycardia can be taken for a PMT: each anti-PMT intervention blocks one atrial event, with a long-short cycle and one beat without BiV pacing
  • Above the MTR, the device can no longer track every atrial event of a pacing-dependent patient: the AV delay lengthens until an atrial event is blocked (Wenckebach behaviour). Most such episodes cause few or no symptoms
  • Rarely, the long-short sequence after a blocked atrial event, with exercise catecholamines and an ischaemic cardiomyopathy, sets off a very fast VT, as here. The device memory held 3 ventricular arrhythmia episodes, all in this setting
  • What to do here: raise the MTR to avoid Wenckebach behaviour, and probably switch the anti-PMT algorithm off, as there was no retrograde conduction at rest (it may still appear on exertion)

Summary

  • Sinus tachycardia at the MTR (120 bpm) taken for a PMT: BiV pacing is lost on one beat after each anti-PMT intervention. Fourteen minutes later the sinus rate exceeds the MTR (Wenckebach behaviour): a fast VT starts after the long cycle that follows a blocked atrial event, and a 41 J shock ends it after failed ATP

Clinical pearl

A too-low MTR is not always harmless: on exertion, each blocked atrial event (Wenckebach, or a sinus tachycardia taken for a PMT) gives a long-short sequence that can, rarely, set off a fast VT, as in this ischaemic heart

Practice out loud

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

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From Boston Scientific CRT — clinical cases by M. Strik. 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.