New ICD algorithm could inhibit inappropriate therapy

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Scott Beau, Arkansas Heart Hospital, Little Rock, USA, and others outlined a new implantable cardioverter defibrillator (ICD) algorithm that could be used to discriminate ventricular tachycardia/ventricular fibrillation noise from pace/sense conducted lead noise, potentially reducing inappropriate therapy due to lead noise.

Beau said: “Damage to the pace/sense conductors of high voltage leads or electrical connection issues can result in ICD sensing artefacts and detection of these artefacts sometimes causes multiple inappropriate shocks.” The purpose of Beau et al‘s study, therefore, was to review whether a new ICD algorithm (SecureSense Noise RV Lead Discrimination, St Jude Medical) that discriminates true ventricular tachycardia/ventricular fibrillation (VT/VF) from lead noise could inhibit inappropriate therapy due to lead noise while appropriately treating VT/VF.

Beau explained: “The new algorithm uses a secondary, far-field channel to confirm any fast rate seen on the near-field channel. Lead noise is detected and therapy is inhibited when the rates of the two channels do not correlate.” He added that if the two channels correlate, VT/VF is detected and therapy is delivered. Other details of the algorithm included that it would check for lead noise at the initial detection, at every redetection point, and prior to delivering initial therapy. Also, Beau reported, undersensing protection was in place to prevent “slow rates or very slow episodes [of VT/VF] from fooling the device into thinking that there is noise to guard against inhibition of appropriate therapy”.

In Beau et al‘s study, ventricular fibrillation and noise electrogram (EMG) clips containing both the near and the far field channels were obtained from patients with ICDs. Beau stated: “Based on the duration of the noise, the noise EMG was classified as sustained noise (causing VT/VF detection) or non-sustained noise (not causing VT/VF detection). These EGMs were then processed through the new algorithm with VF interval set to 280ms and the number of intervals to detect VF set to 12 intervals.”

There were 853 VF induction EGM clips (from 539 patients) assessed in the study, and all were correctly diagnosed as VF using the algorithm. Beau commented: “Two ventricular fibrillation clips had delayed VF diagnosis (<2 seconds) caused by artefacts present in the original data that led to brief undersensing on the far field channel but ultimately therapy was delivered.” He added of 238 sustained noise clips (from 90 lead noise patients), the algorithm successfully detected 231 episodes with at least one lead noise diagnosis (using the algorithm) even if therapy may have been delivered eventually. He said: “But in 217 of the noise clips, the algorithm detected noise continuously and would not have delivered therapy.” Also of 52 non-sustained noise clips, the algorithm successfully detected 47.

According to Beau, the new lead noise algorithm “accurately discriminated VT/VF from pace/sense continuous noise.” He added: “Use of this feature could prevent inappropriate therapy due to lead noise without impacting detection and treatment of true life-threatening arrhythmias and could also identify brief episodes of noise that are potentiallyassociated with lead damage.”

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