SecureSense™ algorithm and undersensing on the discrimination channel
This 77-year-old man received a Quadra Assura™ triple chamber defibrillator for the management of ischemic cardiomyopathy with permanent AF. Episodes of non-sustained RV oversensing were stored in the device memory.
- biventricular stimulation;
- premature ventricular contraction triggering a ventricular tachyarrhythmia; first short cycle on the bipolar channel;
- second short cycle; activation of the noise counter 350 ms after this second cycle;
- first T-classified cycle on the bipolar channel; absence of VS2 marker on the discrimination channel, while the warm-up phase is over, indicative of undersensing on this channel;
- first cycle detected on the discrimination channel;
- undersensing on the discrimination channel followed by second cycle detected without prominent pause between the 2 VS2 markers;
- same sequence;
- the noise counter is at 10 (10 short cycles on the bipolar channel) whereas the VF or VT counter is not filled; diagnosis of non-sustained ventricular oversensing (SNS); the noise counter was not reinitialized in view of the absence of short cycles on the discrimination channel. Diagnostic error by the device; spontaneous termination a few cycles later;
This 71-year-old man received an Ellipse™ VR defibrillator for the management of ischemic cardiomyopathy. An episode of VT was stored in the device memory.
- diagnosis of undersensing on the discrimination channel. The SecureSense™ algorithm was automatically switched to “Passive”;
- VS classified cycles with poor quality of sensing on the discrimination channel (low-amplitude signals, 1 mV for 10 mm amplification <0.5 mV ventricular signals on this channel);
- acceleration of the rate with T classified cycles;
- the VT counter is full (16);
- successful burst and return to sinus rhythm diagnosed after 3 consecutive VS cycles.
The preservation of the highest sensitivity to the detection of ventricular arrhythmias is an absolute requirement of all algorithms that may inhibit the therapies. The SecureSense™ algorithm includes a protection against undersensing on the discrimination channel. The algorithm is withheld if ≥1 event among the following 3 is observed during an episode:
- ≥2 VS2 cycles with a < 0.6 mV amplitude;
- >2,200 ms pause between 2 VS2 cycles;
- detection of a single cycle on the discrimination channel. The SecureSense™ algorithm is automatically reprogrammed to “Passive” during an episode and an undersensing alert appears on the programmer;
During a sustained ventricular tachyarrhythmia, 3 situations are, therefore, possible depending on the quality of sensing on the discrimination channel:
- if sensing is of good quality, the occurrence of short cycles on the discrimination channel regularly reset the noise counter to 0 and the therapies are not inhibited by the algorithm;
- if the quality of sensing is poor (second tracing), a) at least 1 of the 3 criteria is filled, b) the SecureSense™ algorithm is interrupted and reprogrammed to “Passive”, c) an alert appears on the programmer, and d) the therapies are not inhibited by the algorithm;
- in very rare cases, undersensing is intermittent (first tracing) with a risk of inappropriate inhibition of the therapies. However, this risk is very low and, in a large study carried out in our medical center, we observed no prolonged inhibition of the therapies that might have threatened the patients’ well-being. The risk of undersensing an episode for a long duration while not fulfilling at least one of the previously described criteria is very low;
When the sensing quality on the discrimination channel is not flawless, the sensing settings on the discrimination channel cannot be changed (blanking, threshold start, decay delay, and ventricular sensitivity are not programmable). It is, on the other hand, possible to reprogram the discrimination channel on Tip to Can, which also modifies the Morphology Far-Field vector applied in the discrimination. The integration of the distal electrode in the sensing vector to the discrimination channel may, however, limit the algorithm in its ability to prevent the delivery of inappropriate therapies due to lead dysfunction, since the distal electrode is included in the 2 (bipolar and discrimination) sensing vectors. Discordance between the 2 vectors is then less likely if the dysfunction involves the distal electrode. Another solution, in the rare cases of undersensing, consists of programming the algorithm on “Passive”, which will eliminate the risk of inappropriate inhibition of the therapies.