Spurious return to sinus rhythm after burst of ATP

Patient

This 76-year-old man with a history of myocardial infarction received an Atlas dual chamber ICD for sustained VT at 170 bpm.

Main programmed parameters

VF zone at 200 bpm, VT zone at 150 bpm
12 cycles in the VF zone and 12 cycles in the VT zone were needed for the diagnosis
Maximum sensitivity programmed at 0.3 mV
VF zone: six 36-J shocks (maximum amplitude); VT zone: 3 bursts followed by 1 shock at 20 J followed by 3 shocks of maximum strength
Effective discrimination in the VT zone
DDD pacing at 55 bpm; DDI episode pacing mode; post-shock DDI pacing at 60 bpm

Trace

Episode of VT with 2 sequences of ATP; the heart rate after the second burst of ATP at a cycle length of 400 ms was at the limit of the VT zone, though the device diagnosed return of sinus rhythm.

Tracing

AS-VP sequences alternating with AS-VS sequences;
VT with AV dissociation; DDI episode pacing mode after 4 cycles classified T;
Diagnosis of VT after 12 cycles classified T in the V>A arm; trigger of EGM recording;
Burst of ATP;
Unsuccessful burst and continuation of VT; redetection of VT after 6 cycles classified T;
Second burst of ATP;
Continuation of VT, though return of sinus rhythm is erroneously diagnosed (after 5 cycles VS without intervening T cycle) because of slowing of the heart rate below the programmed zone of tachycardia; return to permanent DDD pacing and continuation of VT.

Comments

This tracing underscores again the importance of programming heart rate limits that define the zones of tachycardia. In secondary prevention, the programming is adapted to the characteristics of the clinical tachycardia. This patient presented after an episode of VT at 170 bpm. Consequently, the lower limit of the VT zone had been programmed at 150 bpm (400 ms). The treatment by beta-adrenergic blocker was increased, which might explain the slowing of the VT. Programming of the zones influences the probability of detection and treatment of an episode, as well as the analysis of the success of therapy delivered by the device. In this patient, the persistence of the VT was evident for a cardiologist and for the device (V>A) after the 2 bursts of ATP; however an erroneous diagnosis of return of sinus rhythm was made because of slowing of the rate of the arrhythmia below the lower limit of the VT zone.

Pacing & Defibrillation

ECG

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