SecureSense™ algorithm and lead dysfunction

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Tracing
N° 6
Manufacturer Abbott Device ICD Field Securesence
Patient

This 52-year-old man received a Abbot, single chamber, Fortify Assura™ VR defibrillator for a secondary prevention indication (aborted sudden death due to ischemic cardiomyopathy). A remote monitoring alert and a patient warning (vibration) were issued, prompting an early consultation after 13 episodes diagnosed by the device. The ventricular pacing threshold was stable, the sensitivity acceptable, and the pacing impedance slightly decreased. Two detection zones were programmed, including VF at 200 bpm (300 ms cycle length) and VT at 181 bpm (330 ms cycle length). The SecureSense™ algorithm was programmed ON (between the RV coil and the can).
Graph and trace

Tracing 2A:

Episode of noise on the ventricular lead 

  1. sinus rhythm; the beginning of the tracing shows the VS2 markers on the discrimination channel; from that cycle onward, the VS2 markers are interrupted, corresponding to a deactivation of the noise counter after 255 VS or VP cycles; 
  2. first short cycle (-) on the bipolar channel, indicative of oversensing on the bipolar channel (very low-amplitude signal preceding the QRS);
  3. second short cycle (-) on the bipolar channel; onset of 350-ms warm-up before reactivation of the noise counter;
  4. first F-classified cycles increasing the VF counter; persistence of oversensing on the bipolar channel and absence of detection on the discrimination channel;
  5. accurate sensing of the QRS complexes on the discrimination channel; 
  6. increment in parallel of the VF and noise counters (short cycles are present on the bipolar channel and absent on the discrimination channel);
  7. the VF counter is filled (12); the noise counter is ≥10, prompting the diagnosis of noise on the RV lead and inhibiting the therapies;
  8. return to sinus rhythm diagnosed after 3 consecutive VS cycles (absence of oversensing);

Tracing 2B:

Episode of non-sustained ventricular oversensing (same patient)

  1. sinus rhythm; the presence of VS2 markers on the discrimination channel indicates that the noise counter was activated and that it was increased before the beginning of the tracing;
  2. oversensing with short cycles on the bipolar channel (-) increasing the noise counter (absence of oversensing on the discrimination channel);
  3. the noise counter is at 10 (10 short cycles on the bipolar channel) while the VF or VT counters are not filled; diagnosis of non-sustained ventricular oversensing (SNS).
Comments

This tracing illustrates characteristic aspects of the SecureSense™ algorithm function during an episode of lead dysfunction: 

  1. the VS2 markers are present from the very beginning of the tracing, indicating a prior activation of the noise counter. Once activated, the noise counter is not immediately deactivated, despite the cessation of the arrhythmia or oversensing that caused its activation, since 255 VS or VP cycles are needed on the bipolar channel. Therefore, the noise counter remains active for >4 minutes, for a rate of 60 bpm. This latency illustrates oversensing issues, even when they are highly sporadic and when the arrhythmia counters do not have the time to fill up, representing a major advantage of this algorithm. The repetitive occurrence of sequences, which include, for example, a single oversensed cycle (VS,VS,VS,VS, -) gradually increases the noise counter (recording of an episode of non-sustained noise in the memories), which increases considerably the ability to diagnose oversensing issues compared with standard devices, which require either episodes of non-sustained ventricular arrhythmias with a minimum number of consecutive cycles, or sustained episodes, to trigger a recording;
  2. in the initial phase of lead dysfunction, oversensing may be limited to the bipolar channel and be absent on the discrimination channel. This divergence is the base of the algorithm function. The noise counter increases with each short cycle on the bipolar channel, and the absence of short cycles on the discrimination channel explains why it is not reset to 0. The inappropriate therapies are, therefore, inhibited representing a major advantage from the perspective of quality of life and prognosis;
  3. a therapy inhibited by the SecureSenseTM triggers a patient warning and a remote monitoring alert, shortening the delay between the diagnosis of dysfunction by the device and the onset of medical management, an essential element behind the prevention of inappropriate therapies. It seems nevertheless evident that, while the SecureSenseTM algorithm enables a rapid diagnosis of lead dysfunction and lowers the risk of inappropriate therapies, the dysfunctional lead must be rapidly replaced. It is not advised to rely on the algorithm only to avoid the delivery of inappropriate therapies over the long term, especially since the lead dysfunction tends to increase over time.
 
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