Atrial tachycardia poorly discriminated by a single chamber defibrillator
Patient
This 76-year-old man received a Lumax 540 VR-T single chamber defibrillator in the context of dilated cardiomyopathy with a left ventricular ejection fraction at 25%. An event report (yellow color) was issued in the context of a classified VT1.
Main programmed settings
- VF zone (290 ms limit), VT1 zone (350 ms limit)
- 18/24 cycles in the VF zone and 30 cycles in the VT1 zone were needed for the diagnosis
- Maximum sensitivity programmed at 0.8 mV
- VF zone: ATP one shot, followed by 8 shocks of maximum strength (40 J); VT1 zone: 3 bursts of ATP, followed by 3 ramps of ATP, followed by a single 20-J shock, followed by 7 shocks of maximum strength
- Effective discrimination in the VT zone (onset 20%, stability = 24 ms)
- Pacing mode: VVI at 40 bpm
Trace
Remote tracing
The 3 channels available are 1) the markers with the time intervals, 2) the shock channel (FF = far field) between the coil of the RV lead and the pulse generator, and 3) the right ventricular (RV) sensing channel.
- spontaneous rhythm with probable sinus tachycardia;
- sudden onset tachycardia detected in the VT1 zone. The 38% sudden onset of this episode fulfilled the >20% programmed criterion;
- the morphology criterion was not included in the discrimination. It is noteworthy that the morphology is the same during the tachycardia and during slow, spontaneous rhythm, on the sensing, as well as the shock channels;
- the tachycardia was stable and the 8 ms stability criterion was fulfilled;
- in presence of sudden onset and stable rate, the rhythm was classified as an episode of VT1;
- a burst of ATP was delivered, of which the last 2 cycles are visible;
- successful burst and termination of the arrhythmia.
Comments
This tracing illustrates the challenge represented by the discrimination of atrial tachycardia or flutter. These tachycardias are, like VT, stable rhythms, which start suddenly. In this patient, the signal morphology (not included in the discrimination algorithm) was in favor of a supraventricular origin (same morphology). The sequence of ATP was, therefore, inappropriate, though it did terminate the arrhythmia. The termination by ventricular ATP of an atrial tachycardia that just started is relatively common. Consequently, the termination of the tachycardia by a burst of ATP should not be taken as an argument in favor of a ventricular origin of the tachycardia. In this patient, the device programming was left unchanged.
