Unsuccessful ATP followed by electrical shock for VT
Tracing
Manufacturer Abbott
Device ICD
Field Therapy
N° 32
Patient
This 48-year-old man suffering from dilated cardiomyopathy, with a 25% left ventricular ejection fraction, 140 ms QRS duration and in New York Heart Association functional class III, received a Promote triple chamber CRT-D for secondary prevention, and was seen in consultation for electrical shock.
Main programmed parameters
- VF zone at 214 bpm, VT-2 zone at 181 bpm, VT-1 zone at 150 bpm
- 12 cycles in the VF zone, 12 cycles in the VT-2 zone and 15 cycles in the VT-1 zone were needed for the diagnosis
- Maximum sensitivity programmed at 0.3 mV
- VF zone: six 36-J shocks (maximum strength); VT-2 zone: 2 bursts followed by single 6-J shock followed by 3 shocks of maximum strength; VT-1 zone: 6 bursts followed by 10-J shock, followed by 2 shocks of maximum strength
- Effective discrimination in the VT-1 and VT-2 zones
- DDIR pacing mode at 75 bpm; DDI episode pacing mode; DDI post-shock pacing mode at 60 bpm
Graph and trace
Narrative
The narrative suggests an acceleration of the arrhythmia by ATP. The episode, initially detected in the VT-1 zone, was treated with 1 burst of ATP, which accelerated the tachycardia to the VT-2 zone. Two additional, probably unsuccessful bursts of ATP were delivered, followed by a probably successful 6-J shock and 37 Ohms impedance.
Tracing
- Atrial and biventricular (AP-BP) paced rhythm at the sensor indicated rate (SIR); late VES sensed in the post atrial ventricular safety pacing (VSP) window (64 ms post atrial pacing), ventricular paced event 120 ms after the atrial stimulus;
- Tachycardia with AV dissociation: VT; the initial cycles are unclassified before being classified in the VT-2 zone;
- DDI episode pacing mode after 3 T2;
- Diagnosis of VT-1 in the V>A arm; 15 cycles are sensed in the VT-1 (VT-1 counter full) versus 8 cycles only in the VT-2 zone (VT-2 counter unfilled); the average of the last 4 cycles: (344 + 367 + 332 + 328) / 4 = 340 ms contributes to the diagnosis made by the device, as well as set the ATP burst rate; it is noteworthy that the morphology of the VT is similar to the reference QRS morphology (100), though this criterion is not included in the V>A discrimination arm;
- First VT-1 zone therapy: burst of 8 stimuli at fixed cycle length (80% of 340 ms = 272 ms);
- Unsuccessful burst, acceleration of the ventricular rate and redetection in the VT-2 zone after 12 T2 classified cycles; it is noteworthy that the morphology of a redetection after delivery of therapy is no longer analyzed;
- First therapy in VT-2 zone: burst of 8 stimuli at fixed rate;
- Unsuccessful burst and redetection in the VT-2 zone;
- Second therapy in VT-2 zone: second burst;
- Unsuccessful burst and redetection in the VT-2 zone; charge of the capacitors;
- Third therapy in the VT-2 zone: delivery of 6-J shock;
- 1-sec post-shock blanking and absence of pacing for 2 sec, which explains the pause in this pacemaker-dependent patient;
- Successful shock and diagnosis of restoration of sinus rhythm; DDI post-shock pacing mode.
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EGM recordings
In the VT-1 zone, the series of therapies ends as soon as the rate slows and falls below the programmed VT zone limit, or when all therapies have been exhausted. In contrast, in this patient, the initial burst accelerated the tachycardia, which was then detected in the VT-2 zone, prompting the delivery of therapies programmed for that zone near 200 bpm, namely 2 bursts of ATP followed by a low-energy shock.
Various settings can be programmed to optimize the success of ATP. The faster the pacing rate, the higher the likelihood of terminating as well as accelerating VT. The number of paced cycles also influences the outcome of ATP. Usually, 5 to 15 consecutive paced cycles are programmed with each salvo. Too few cycles of ATP may not penetrate the tachycardia circuit, leaving the salvo ineffective. Conversely, too many ATP cycles may terminate the VT, then immediately re-induce it, accelerate it, or transform it into VF.