Poorly discriminated ventricular tachycardia
Patient
This 59-year-old man received a Lumax 740 DR-T dual chamber defibrillator for the management of episodes of VT in the background of dilated cardiomyopathy. An event report (yellow color) was issued in the context of a classified VT1 and SVT.
Main programmed settings
- VF zone (260 ms limit), VT2 zone (290 ms limit), VT1 zone (340 ms limit)
- 8/12 cycles in the VF zone, 16 cycles in the VT2 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); VT2 zone: 2 bursts of ATP, followed by 2 ramps of ATP, followed by 8 shocks of maximum strength; VT1 zone: 5 bursts of ATP, followed by 5 ramps of ATP, followed by a single 20-J shock, followed by 7 shocks of maximum strength;
- Effective discrimination in the VT2 and VT1 zones (SMART discrimination)
- Pacing mode: DDD at 60 bpm
Trace
Remote tracing 1
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 initially in the VT1 zone with a 1:1 atrioventricular ratio; the ventricular events are classified Tsin (sinus tachycardia);
- interruption of retrograde conduction with faster ventricular than atrial rate (indicative of VT); discrimination in the PP>RR zone;
- diagnosis of VT1 in the PP>RR arn;
- delivery of 6 sequences of ATP.
Remote tracing 2
- tachycardia in the VT1 zone with 1:1 atrioventricular ratio; the ventricular events are classified Tsin (sinus tachycardia). It is noteworthy that the ventricular morphology is similar to that of the previous episode;
- classification SVT in the PP=RR arm; the average PP and RR at initial classifications = 332 and 336 ms, respectively. Stable rhythm, with 8-ms stability for a 24 ms programmed threshold. Stable PP cycles and PR interval without monotonous change. In this case, the sudden onset criterion was not fulfilled since it measured 18% for a 20% programmed threshold. Consequently, the diagnosis made by the device was SVT (sinus tachycardia).
Comments
During a 1:1 tachycardia, the observation of a transitory ventriculo-atrial block is diagnostic of VT. The second episode was diagnosed as SVT (sinus tachycardia) by the device. The differential diagnosis between VT and sinus tachycardia is highly challenging, if not impossible, on the basis of the analysis of this tracing only. The diagnosis of the first episode is unequivocal, as the interruption of retrograde conduction (V>A) discloses the ventricular origin of the tachycardia. In a patient presenting with multiple episodes of 1:1 tachycardia, all tracings must be scrutinized, in search of anterograde (SVT) or retrograde (VT) block, confirming the diagnosis.
