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).
Tracing 2A:
Episode of noise on the ventricular lead
- 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;
- first short cycle (-) on the bipolar channel, indicative of oversensing on the bipolar channel (very low-amplitude signal preceding the QRS);
- second short cycle (-) on the bipolar channel; onset of 350-ms warm-up before reactivation of the noise counter;
- first F-classified cycles increasing the VF counter; persistence of oversensing on the bipolar channel and absence of detection on the discrimination channel;
- accurate sensing of the QRS complexes on the discrimination channel;
- increment in parallel of the VF and noise counters (short cycles are present on the bipolar channel and absent on the discrimination channel);
- the VF counter is filled (12); the noise counter is ≥10, prompting the diagnosis of noise on the RV lead and inhibiting the therapies;
- return to sinus rhythm diagnosed after 3 consecutive VS cycles (absence of oversensing);
Tracing 2B:
Episode of non-sustained ventricular oversensing (same patient)
- 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;
- oversensing with short cycles on the bipolar channel (-) increasing the noise counter (absence of oversensing on the discrimination channel);
- 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).
This tracing illustrates characteristic aspects of the SecureSense™ algorithm function during an episode of lead dysfunction: