Sorin Sensing and Detecting episodes

1 - SENSITIVITY

2 - DETECTION ZONES

3 - DETECTION OF AN EPISODE OF VENTRICULAR ARRHYTHMIA

 

1 - SENSITIVITY

V sensitivity (sensing)

The ventricular sensitivity determines the minimum signal sensing threshold from the ventricle. The defibrillator provides an automatic ventricular sensitivity control.

Automatic ventricular sensitivity control: Post-V sensing

When sensing a spontaneous ventricular event, the amplitude is measured and the ventricular sensitivity is automatically set according to this measurement until the next ventricular event. Nominal 0,4  mV, [0,4 ; 4]

The ventricular sensing threshold depends on the sensed R wave amplitude :

R wave amplitude < 1.6 mV

In this case, the ventricular sensing threshold is set at the programmed ventricular sensitivity until the next R sensed event.

R wave amplitude ranges from 1.6 mV to 4 mV

sensing_sorin1.png

 

In this case, the ventricular sensing threshold isset :

  1. between 1/4 and 1/2 (coefficient varies linearly from 1.6 to 6.2 mV) of the measured amplitude (during 156 ms following the amplitude measurement),
     
  2. at 1/4. of the measured amplitude (between 156 and 500 ms following the amplitude measurement),
     
  3. to the programmed ventricular sensitivity (500 ms following the amplitude measurement).

R wave amplitude ranges from 4 mV to 6 mV

sensing_sorin1.png

 

In this case, the ventricular sensing threshold is set :

  1. between 1/4 and 1/2 (coefficient varies linearly from 1.6 to 6.2 mV) of the measured amplitude (during 156 ms following the amplitude measurement),
     
  2. at1/4 of the measured amplitude (between 156 and 500 ms following the amplitude measurement),
     
  3. to the programmed ventricular sensitivity or 1 mV if the programmed ventricular sensitivity is lower (500 ms following the amplitude measurement). In case of arrhythmia suspicion, the ventricular sensing threshold is always set to the programmed ventricular sensitivity.

R wave amplitude > 6 mV

sensing_sorin1.png

 

In this case, the ventricular sensing threshold is set :

  1. at 3 mV (during 156 ms following the amplitude measurement),
     
  2. at 1.5 mV (between 156 and 500 ms following the amplitude measurement),
     
  3. to the programmed ventricular sensitivity or 1 mV if the programmed ventricular sensitivity is lower (500 ms following the amplitude measurement). In case of arrhythmia suspicion, the ventricular sensing threshold is always set to the programmed ventricular sensitivity.

Automatic ventricular sensitivity control: Post-V pacing

To avoid T-wave oversensing, following ventricular pacing, the ventricular sensitivity is set as follows: Nominal 0,8  mV, [0 ; 2]

  1. For the first 500 ms following the pacing, the ventricular sensing threshold is set at the programmed ventricular sensitivity increased by the V margin post V pacing.
     
  2. After 500 ms, the ventricular sensing threshold is set to the programmed ventricular sensitivity (or 1 mV if the programmed ventricular sensitivity is lower). In case of arrhythmia suspicion, the ventricular sensing threshold is always set to the programmed ventricular sensitivity. 

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                                                    Brady Parameters screen

 

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                                       Brady Parameters + A and V sensing screen

 

 

2 - DETECTION ZONES

Single-chamber ICD

The defibrillator analyzes all ventricular events sensed in the detection zones. The device classifies each ventricular event according to cycle length and categorizes each majority rhythm as either:

  • VF (ventricular fibrillation) or
     
  • VT/VTLC, SVT/ST (tachycardia) or
     
  • SR (slow rhythm) or
     
  • No majority

If the rhythm is a tachycardia, three further criteria (RR stability, long cycle occurrence, sudden onset ) may be used to discriminate ventricular tachycardia from supraventricular or sinus tachycardia. After a VT or VF majority is reached and this majority persists for a programmable number of persistence cycles, ICD delivers the programmed ATP or loads the shock capacitors. ICD uses the tachycardia sorting template to classify rhythms with tachy majority. This sorting depends on RR stability (stable or unstable), VT Long Cycle occurrence (VTLC) and acceleration (sudden or gradual) at the tachycardia onset (ventricular origin or none).

The programmer provides predefined tachycardia detection criteria:

  • Rate only: Use ventricular rate only.
     
  • Stability: Use ventricular stability.
     
  • Stability+: Use ventricular stability and search for a VT long cycle.
     
  • Stability/Acceleration: Use ventricular stability and ventricular sudden onset.
     
  • Stability+/Acceleration: Use ventricular stability, ventricular sudden onset and search for a VT long cycle.

sensing_sorin4.png 

                                             Tachy Parameters screen of SC ICD

 

Dual-chamber ICD

The defibrillator analyzes all atrial and ventricular events sensed in the detection zones. The device classifies each ventricular event according to cycle length and categorizes each majority rhythm as either:

  • VF (ventricular fibrillation) or
     
  • VT/VTLC, SVT/ST (tachycardia) or
     
  • SR (slow rhythm) or
     
  • No majority

If the rhythm is a tachycardia, five further criteria (RR stability, long cycle occurrence, PR association, sudden onset and chamber of origin of acceleration) may be used to discriminate ventricular tachycardia from supraventricular or sinus tachycardia. After a VT or VF majority is reached and this majority persists for a programmable number of persistence cycles, ICD delivers the programmed ATP or loads the shock capacitors.

ICD uses the tachycardia sorting template to classify rhythms with tachy majority. This sorting depends on RR stability (stable or unstable), PR association (N:1, 1:1, or none), VT Long Cycle occurrence (VTLC) and acceleration (sudden or gradual) at the tachycardia onset (atrial origin, ventricular origin or none).

The programmer provides predefined tachycardia detection criteria:

  • Rate only: Use ventricular rate only.
     
  • Stability: Use ventricular stability (ventricular sensing only).
     
  • Stability+: Use ventricular stability and search for a VT long cycle (ventricular sensing only).
     
  • Stability/Acceleration: Use ventricular stability and ventricular sudden onset (ventricular sensing only).
     
  • Stability+/Acceleration: Use ventricular stability, ventricular sudden onset and search for a VT long cycle (ventricular sensing only).
     
  • PARAD: Use ventricular stability, PR association, sudden onset and origin at onset (atrial and ventricular sensing).
     
  • PARAD+: Use ventricular stability, search for a VT long cycle, PR association, sudden onset and origin at onset (atrial and ventricular sensing).

Note: PARAD/PARAD+ should not be used if there is no atrial lead or in case of insufficient atrial signal quality.

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                                             Tachy Parameters screen of DC ICD

Both Single and Dual Chamber ICD

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                 Parts of Detection Parameters screen of SC/DC ICD

 

Majority Rhythm

The defibrillator applies the majority (X% of Y cycles) to determine the predominant rhythm:

  • (X/Y) Y: number of cycles used by the device to analyze the ongoing rhythm.
  • (X/Y) X: minimum percentage of cycles the device needs to classify the ongoing rhythm.

sensing_sorin8.png

3 - DETECTION OF AN EPISODE OF VENTRICULAR ARRHYTHMIA

Persistence

The persistence criterion of Slow VT, VT and VF requires the arrhythmia to remain in the majority for a programmed number of cycles. The defibrillator then applies the programmed therapy.

The VT, slow VT and VF persistence counters are independent.

SORIN ICD only resets the persistence cycle counter when it finds some other majority rhythm, not when applying therapy.

Note: An episode of tachyarrhythmia is terminated when slow rhythm majority is detected. The sequential therapies are then reinitialized. 

Slow VT persistence: Nominal 12 cycles, [4 ; 200]

VT persistence: Nominal 12 cycles, [4 ; 200]

VF persistence: Nominal 6 cycles, [4 ; 20]

Long Cycle Persistence Extension

Long cycle persistence extension is a programmable number of cycles added to the persistence in case of VTLC search. Persistence for other rhythm analysis remains the same. Nominal 10 cycles, [0 ; 16]

Note: Only programmable if Detection criteria is programmed on: Stability+ or Stability+/Acceleration or PARAD+.

Episode labeling

Labeling episode is set when the persistence criterion is obtained for the first time. It could be VF, VT, slow VT, VT->SVT/ST or SVT/ST.

Example of persistent rhythm in VF

After VF majority is reached every 8 sliding cycles and this majority persists for a programmable number of persistence cycles (6 in this case), ICD loads the shock capacitors

sensing_sorin9.png

 

 

Example of persistent rhythm in VT

After a VT majority is reached every 8 sliding cycles and this majority persists for a programmable number of persistence cycles (6 in this case), ICD delivers the programmed ATP.

sensing_sorin10.png

 

 

Example of persistent rhythm in slow VT zone

After a VT majority is reached every 8 sliding cycles and this majority persists for a programmable number of persistence cycles (6 in this case) and the Tachy cycles mean is in range of a tachy therapy zone, ICD delivers the programmed ATP.

sensing_sorin11.png

 

Redetection of an episode of ventricular arrhythmia

After therapies, majority criterion is reset, persistence counters are not reset and acceleration criterion is set to VENTRICULAR.

Redetection phase is also based on analysis of criterion (rate, ventricular stability, search for a VT long cycle, PR association). A VT or VF majority rhythm (X% of Y cycles) is required to apply the next therapy. It means that a count of 6 cycles is required at least

 

Examples of post ATP redection

To engage the next therapy program, the device needs to analyze only the majority rhythm (except acceleration criterion).

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Example of post shock redection

To engage the next therapy program, the device needs to analyze only the majority rhythm (except acceleration criterion).

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Episode end

When the device reaches SR majority criterion (slow rhythm), current episode is closed and stored in ICD memory. Detection criteria and therapy programs are reset.

Non sustained episode

In the following situation:

  • majority criterion VF, VT, VTLC or SVT/ST is reached
     
  • persistence criterion not yet fulfilled and
     
  • finally SR majority criteria is obtained,

the device save this non sustained episode . For memory management, the priority level of this episode type is low. Labeling episode is “Non Sust.” Detection criteria are reset.

 

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