Programming the Abbott defibrillators: latest guidelines
For a primary prevention indication, a 30-cycle ventricular tachycardia (VT) zone between 187 and 250 bpm and a 30-cycle ventricular fibrillation (VF) zone >250 bpm must be programmed. For a secondary prevention indication, these 2 zones may be supplemented by an additional VT zone 10 to 20 bpm slower than the clinical VT. These programming guidelines correspond to those formulated in the main document:
- In primary or secondary prevention, whether in the VT or VF zone, the device programming must allow a minimum duration of 6 seconds (or approximately 30 cycles depending on the rate) before the detection counter is full, to limit the overall number of appropriate or inappropriate therapies delivered (class I indication)
- In primary prevention, the slowest zone of therapy must be programmed between 185 and 200 bpm to limit the overall number of therapies delivered (class I indication)
- In secondary prevention, when the cycle of the clinical VT is known, a VT zone 10 à 20 bpm slower than that tachycardia should be programmed (class IIA indication).
- In all patients presenting with structural heart disease who are at risk of developing an organized VT, 1 sequence of ATP should be programmed (unless it is known to be unsuccessful or arrhythmogenic) in the zones of VT and VF with a view to obviate the need to deliver an electric shock (class I indication).
- A burst of ≥8 stimuli instead of a ramp (class I indication) and a cycle length between 84 and 88%of the tachycardia cycle length (class I indication) should be programmed.
- Except in patients who present with an abnormal atrioventricular conduction, the discrimination algorithms must be programmed to a rate of 230 bpm to limit the risk of inappropriate therapy (class I indication).
- It is recommended to turn off the clocks (time-out) that force the delivery of therapies beyond a set duration, including when the device diagnoses an SVT (class IIB indication).
- it is based on an analysis of the congruence of the length of the ventricular cycles present on the bipolar and the discrimination channels. A noise counter is integrated in the decision to deliver or inhibit the therapies. Once active, it increases with each short cycle sensed by the bipolar channel, and is reset to 0 after 2 short cycles sensed by the discrimination channel;
- the algorithm suspects oversensing and inhibits the therapies, should a discordance between the 2 channels be detected, i.e. the presence of short cycles on the bipolar channel, which increase the arrhythmia counter, in absence of short cycles on the discrimination channel;
- the algorithm suspects a true ventricular arrhythmia and does not inhibit the programmed therapies when both channels are concordant: i.e. short cycles are detected on the bipolar channel as well as on the discrimination channel;
- the algorithm diagnoses non-sustained episodes of noise when the noise counter increases without saturating the arrhythmia counter; this allows the identification of oversensing issues, even when sporadic;
- a protection has been put in place against the risk of inhibition of the therapies in presence of undersensing by the discrimination channel, which is indispensable to preserve the highest sensitivity of the device to diagnose ventricular arrhythmias;
- this algorithm operates together with the programming of patient warnings (vibrations of the pulse generator) and remote monitoring alerts (Merlin.net™), which shorten the delay between the diagnosis of oversensing by the device and its medical management.
- if the noise counter is <10: a) the VT/SVT discrimination scrutinizes the VT zone before delivering a first therapy; b) the first therapy is delivered in the VF zone if it consists of ATP delivered before or during the charge. If the ICD’s capacitors are being charged, the noise counter is verified one more time at the end of the charge and, if <10 the shock is delivered whereas if it is ≥10 it is dumped. Once a first therapy delivered, the SecureSense™ algorithm is withheld until the end of the episode, i.e. until the return to sinus rhythm.
- if the noise counter is ≥10 when the VT or VF counter is full, oversensing is diagnosed and the therapies are inhibited. The count of SecureSense™ is verified with each redetection of VT or VF (every 6 cycles). If the counter remains ≥10, the therapies are inhibited.
To preserve the highest sensitivity and lower the risk of inhibiting the therapies due to undersensing on the discrimination channel, the algorithm incorporates a protection, which cancels the inhibition of therapies, should sensing on this channel be flawed. The algorithm is automatically reprogrammed to “Passive” during the episode, enabling the delivery of therapy. The algorithm is interrupted if one of these three events occurs during an episode: 1) ≥2 VS2 cycles with a <0.6 mV amplitude, 2)
There is a characteristic discordance between the bipolar channel, where the cycles are short and disorganized, and the discrimination channel, which shows an unremarkable tracing. The noise counter is activated after 2 instantaneous short cycles (classified -) on the bipolar channel + 350 ms (corresponding to the warm-up phase). The first VS2 marker appears thereafter on the discrimination channel at the time of the next QRS complex. The VF counter increases with each F-classified cycle (multiple oversensing); it is full when it reaches the programmed value of 12. The noise counter increases in parallel with each short cycle on the bipolar channel. This counter is never reset to 0 since no short cycle is present on the discrimination channel. When the VF counter is filled (12), the noise counter is above or equal to 10 (11). The device diagnoses oversensing (RV lead noise) and inhibits the therapies. After each redetection (6 F-classified cycles) on the bipolar channel, the noise counter undergoes a new analysis. If, as in this example, the counter remains ≥10, the therapies are inhibited since the device has diagnosed persistent oversensing.
The same characteristic aspect of oversensing is apparent, with short cycles present on the bipolar channel and absent on the discrimination channel (the QRS complexes are accurately sensed). The episodes of oversensing are brief and the VF counter is never filled, while the noise counter has reached 10. The noise counter is never reset to 0 since there is no short cycle on the discrimination channel. An episode of non-sustained oversensing (NSLN, NSN on the new devices) is diagnosed. The NSLN or NSN marker appears thereafter on the tracing each time the noise counter reaches a multiple of 10. A remote monitoring alert is triggered after a programmable number of similar non-sustained episodes of noise. This algorithm, therefore, discloses the occurrence of oversensing issues, including when they are highly intermittent, representing an important contribution to an early diagnosis of lead dysfunction, which often manifests itself initially as very brief episodes of short ventricular cycles.