Accurate discrimination of ventricular tachycardia by a dual chamber defibrillator
Patient
This 36-year-old man received a Lumax 540 DR-T dual chamber defibrillator in the context of non-obstructive, hypertrophic cardiomyopathy, with a 32-mm septum thickness and episodes of non-sustained VT. An event report (yellow color) was issued in the context of a classified VT1.
Main programmed settings
- VF zone (270 ms limit), VT1 zone (360 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: 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 VT1 zone (SMART discrimination)
- Pacing mode: DDD at 60 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 sensing channel (A), and 4) the RV sensing channel;
- spontaneous rhythm in the atrium and the ventricle;
- ventricular extrasystole;
- probable VT with retrograde conduction;
- interruption of retrograde conduction (diagnosis ascertained by excess of ventricular compared with atrial events)
- atrioventricular dissociation;
- diagnosis of VT after 26 cycles classified VT1; discrimination in the PP>RR arm. The mean PP (606 ms) during initial classification was the average of 4 PP cycles (383 + 672 + 695 + 680) before the classification, while the average RR (344 ms) during initial classification was the average of 4 RR cycles (344 + 359 + 328 + 344) before the classification;
- burst of ATP (the last 5 stimuli are visible);
- successful burst and termination of the arrhythmia;
- end of episode after 12 VP or VS cycles.
Comments
Dual chamber discrimination is based on a combined analysis of the atrial and ventricular electrograms. When, as on this tracing, the ventricular cycle (the average of 4 ventricular cycles of tachycardia) is shorter than the atrial cycle (the average of 4 atrial cycles of tachycardia), the tachycardia is classified as VT by the SMART algorithm and no other discrimination criterion is considered.
