Accurate discrimination of sinus tachycardia by dual chamber defibrillator

Patient

This 61-year-old man received a Lumax 740 DR-T dual chamber defibrillator in the context of ischemic cardiomyopathy with a depressed left ventricular ejection fraction. An event report (yellow color) was issued in the context of classified SVT.

Main programmed settings

VF zone (280 ms limit), VT1 zone (400 ms limit)
8/12 cycles in the VF zone and 26 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: 5 bursts of ATP, followed by 5 ramps of ATP, followed by a single 14-J shock, followed by a single 20-J shock, followed by 6 shocks of maximum strength
Effective discrimination in the VT1 zone (SMART discrimination)
Pacing mode: DDD at 50 bpm

Trace

Remote tracing

The 4 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, 3) the atrial (A) sensing channel, and 4) the right ventricular (RV) sensing channel.

tachycardia in the VT1 zone with a 1:1 atrioventricular ratio. The ventricular events are classified Tsin (sinus tachycardia);
classification SVT in the PP = RR arm; (the average PP and RR intervals during the initial classifications both measure 379 ms; stable rhythm, with a 2 ms stability for a 24-ms programmed threshold; stable PP and PR intervals without monotonous change). In this case, the sudden onset criterion was not fulfilled, since it measured 1% for a 20% programmed threshold. Consequently, the diagnosis made by the device was SVT (sinus tachycardia);
gradual slowing of the heart rate at the end of exercise and exit from the VT1 zone (VS cycles).

Comments

The vast majority of 1:1 tachycardias are supraventricular in origin, while VT with 1:1 retrograde conduction represents only 10% of these tachycardias. The dual chamber discrimination algorithms must be systematically activated in patients with preserved atrioventricular conduction and properly functioning atrial lead. On the other hand, in presence of complete atrioventricular block, these algorithms are useless, since all spontaneous tachycardias are of ventricular origin. In a patient whose atrial lead is dysfunctional and either under- or oversenses, the programming of simple chamber discrimination should be considered in order to avoid erroneous classifications and the risk of delivering inappropriate therapies.

This was an episode of accurately discriminated sinus tachycardia, with gradual acceleration of a stable rhythm.

Pacing & Defibrillation

ECG

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