Specific noise diagnosis algorithm
Patient with dilated cardiomyopathy implanted with a single-chamber ICD (Protecta XT VR); this tracing shows the functioning of the specific noise diagnosis algorithm on the right ventricular lead.
The graph shows a characteristic scatter plot pattern with high interval to interval variability and very short ventricular cycles at the limit of the programmed blanking value; no therapy was delivered, the device having diagnosed an oversensing due to noise on the lead.
- the EGM shows intervals with disorganized, highly variable, anarchic amplitude and frequency unrelated to the QRS complexes on the bipolar channel, with some signals saturating the amplifiers and certain intervals at the limit of the programmed blanking; there is much less oversensing in the far-field channel;
- the VF counter is filled but no therapy is delivered, the device having made the diagnosis of oversensing due to lead dysfunction.
The lack of long-term reliability of ICD leads represents one of the main limitations of implantable devices and constitutes one of the most difficult challenges for the manufacturers involved. In the aftermath of the problems of the Fidelis lead, preventing the occurrence of multiple inappropriate shocks through early diagnosis of signs of dysfunction and the development of stronger leads has become a top priority for MedtronicTM. The latest devices are equipped with 2 algorithms specifically dedicated to the diagnosis of lead dysfunctions and the prevention of inappropriate shocks.
1) the LIA (Lead Integrity Alert): the occurrence of inappropriate therapies for lead dysfunction is usually preceded by a sudden change in impedance and/or short episodes of oversensing and/or recording of very short isolated ventricular cycles. The LIA algorithm was developed to generate a warning in response to a suspected lead dysfunction and to delay the occurrence of therapies by monitoring the bipolar and integrated bipolar impedances, the frequency of non-sustained VT episodes, and the frequency of very short ventricular intervals. A lead dysfunction is identified if at least 2 of the following 3 criteria are met within the past 60 days:
- the pacing impedance for either polarity (bipolar and/or integrated bipolar) is lower than 50% or greater than 175% of the baseline value which corresponds to the median of the previous 13 daily measurements;
- the ventricular sensing integrity counter (short ventricular intervals ≤ 130ms) is incremented by at least 30 over a period of 3 consecutive days;
- the device senses 2 rapid non-sustained VT episodes with a 5-beat RR interval average of less than 220 ms. When a lead dysfunction is suspected, the device transmits a specific remote monitoring alert notification, with an audible alert emitted every 4 hours until the ICD is interrogated and the number of intervals required for detection is automatically extended to 30/40 in order to delay (but not prevent) the occurrence of inappropriate therapies.
2) the noise discrimination algorithm on the RV lead (RV Lead noise discrimination): the aim of this algorithm is to identify the EGMs that are characteristic of a lead fracture and to withhold therapy based on a comparison of the amplitude (peak-to-peak) of the signals collected in the far-field channel versus those collected in the near-field channel. The amplitude (peak-to-peak) of 12 consecutive signals is analyzed through a sliding window using a counter. When the number of intervals required for the sensing of a VT or VF is reached, if 3 of the last 12 sequences (amplitude comparison in the far-field channel and the near-field channel) are classified as "noise", detection is interrupted, therapy is withheld and a "RV Lead Noise" alert is triggered (an audible alert is emitted by the device every 4 hours until the device is interrogated, a remote monitoring alert notification is also transmitted if this specific alert has been programmed). This algorithm can be programmed to OFF, ON or ON + Timeout OFF. In the latter case, a specific duration is programmed; if the oversensing of noise persists beyond this time (15 seconds to 2 minutes), the therapies will be delivered despite the diagnosis made by the device.
In practice, in the presence of a lead dysfunction, the LIA allows a much earlier diagnosis than the second algorithm. Indeed, the LIA alerts in the presence of short intervals and non-sustained VT episodes whereas the noise algorithm intervenes only if the initial counter is filled (30/40) and hence when the oversensing is prolonged. This second algorithm is therefore only useful if, despite LIA alerts, no provision has been made or if the very first oversensing episode is sufficiently sustained to fill the initial counters (very rare presentation). It should be noted that the LIA often enables early diagnosis, delays but does not inhibit the therapies and generates an alert while the noise algorithm allows an often-later diagnosis but inhibits the therapies.