Sustained VT treated by a burst

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Tracing N° 1
Biotronik Devices: ICD Field: Therapy
Patient

This 67-year-old man received a Lumax 540 VR-T single chamber defibrillator in the context of ischemic cardiomyopathy with a 20% left ventricular ejection fraction; event report (yellow color) issued in the context of a classified ventricular tachycardia (VT)2.

 

Main programmed settings

  • Ventricular fibrillation (VF) zone (280 ms limit), VT2 zone (420 ms limit) and VT1 zone (480 ms limit) 
  • 12/16 cycles in the VF zone, 24 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: delivery of a single burst of ATP one shot, followed by 8 shocks of maximum strength (40 J); VT2 zone: 4 bursts, followed by 4 ramps, followed by 1 shock at 20 J, followed by 7 shocks of maximum strength; VT1 zone: 4 bursts, followed by 4 ramps; no shock programmed
  • Effective discrimination in both VT zones
  • Pacing mode: VVI at 30 bpm 
Graph and 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.

  1. spontaneous rhythm; the label “PermVVI” at the beginning of the tracing indicates that the defibrillator operates in the programmed VVI pacing mode;
  2. ventricular extrasystole (VES);
  3. sudden onset of tachycardia detected in the VT2 zone, with change in the QRS morphology compared to sinus rhythm; the label “onset” marks the first cycle where the sudden onset criterion was confirmed; the averages of the 4 previous (680 ms) and 4 following (367 ms) cycles explain the sudden onset value (46%) that is posted;
  4. classification of VT2 episode after 24 cycles in the VT2 zone without interposed cycle classified VT1 or VS; the average RR at the time of initial detection (413 ms) corresponds to the average of the 4 cycles preceding the diagnosis; the posted stability value (3 ms) is the difference between the longest and the shortest cycles among the last 4 cycles preceding the classification. It is noteworthy that the sample rates of the tracing (128 Hz) versus the defibrillator (512 Hz starting with Lumax 740 model) are different. Consequently, the resolution of the tracing is 8 ms versus 2 ms by the device, explaining the less precise measurements on the tracing than those used by the device, for example in the monitoring of stability. The coupling of the last 4 cycles shown on this tracing is 414 ms, implying a 0-ms stability. The more precise analysis by the device indicates a 3-ms variability among these 4 cycles;  
  5. the burst of ATP delivered is not visible;
  6. termination of the arrhythmia;
  7. end of the episode after 12 consecutive cycles classified Vs (12/16 Vs); the average RR at the end of the episode (884 ms) corresponds to the average of the 4 cycles preceding the end of the episode.

Programmer tracing (same episode)

The 3 channels are the same as for the remote tracing;

  1. visualization of the burst (10 stimuli at a fixed 80% of the rate of the tachycardia); the label “PermVVI” at the end of the burst indicates that the defibrillator remains in a permanent VVI pacing mode during the episode of tachycardia and after the ATP sequence.
Comments

The EGM transmitted by telemedicine lasts a maximum of 30 sec before the initial classification, followed by a maximum of 10 sec before the classification of the end of the episode. Since the maximum amount of information that can be transmitted is limited, these values may sometimes be smaller. The transmitted EGM correspond to the EGM retrieved by the programmer, with some filtering of the baseline to limit the amount of transmitted information.

The EGM retrieved by the programmer do not last longer than 3 min 30 sec per episode. The EGM recording begins 5 sec before the sudden onset diagnosis or 30 sec before the classification, if the sudden onset criterion is not fulfilled. If the episode is >3.5 min, the recording is interrupted, while the start and end of the episode remain visible.

This tracing is an example of VT terminated by a burst of ATP, the first therapy programmed for the treatment of VT at <200 bpm. This painless therapy, which limits the consumption of energy and preserves the battery longevity, must be favored. In a <200 bpm VT zone, ATP can be programmed in a majority of patients suffering from heart failure and treated for secondary or primary prevention indications, unless it has previously been found ineffective or arrhythmogenic. 

Theoritical features / Basic concepts

Shock therapie Anti-tachycardia Pacing   SHOCK THERAPIES Shock therapies ICD were originally invented to terminate malignant ventricular arrhythmias using DC shocks. Cardioversion is the delivery of a DC shock synchronized to the rising edge of the R wave of the electrocardiogram to terminate a supraventricular or a ventricular tachyarrhythmia, whereas defibrillation is the delivery of an unsynchronized DC shock to terminate VF. During VF, the instability and low voltage of the ventricular EGM sometimes precludes the synchronization of ICD shocks. Medtronic ICDs systematically seek to synchronize the shock delivery, including in the VF zone. Several shock characteristics are programmable, including vector, amplitude and number of shocks delivered. Shock waveform: early defibrillators...