Sensing Integrity Counter Research Articles

Incidence of nonphysiologic short VV intervals detected by the sensing integrity counter with integrated bipolar compared with true bipolar leads: clinically inconsequential or cause for concern?

The need to detect impending implantable cardiac defibrillator (ICD) lead failure has grown. Automated sensing diagnostics have been developed for this reason. The sensing integrity counter (SIC) is one such oversensing diagnostic, which forms an integral part of the Medtronic™ lead integrity alert (LIA) feature on implantable defibrillators. It records nonphysiologic short VV intervals (NPSVVIs). It is unclear whether SIC data derived from integrated bipolar (IBP) leads need to be interpreted differently when compared to true bipolar (TBP) leads. We hypothesized that IBP ICD leads by virtue of a larger "antennae" may generate more NPSVVIs on than TBP leads, leading to more false-positive SIC counts. Equal durations of remote monitoring records of 44 patients (mean age of 65.9 ± 2.2 years, 52 % female) with IBP ICD leads and Medtronic (MDT) generators (IBP group) were compared with those of 44 randomly selected patients (64.0 ± 2.2 years, 24 % female) who had TBP ICD leads and MDT generators (TBP group). Mean surveillance time, defined as the time over which the cumulative SIC count was acquired, was 614 ± 44 days (TBP group) vs. 620 ± 49 days (IBP group, p = ns). The mean time of follow-up following the first documented short VV interval was 115.2 months in the integrated bipolar group and 66.9 months in the true bipolar group. Leads on advisory were excluded from the study. A total of 26/44 patients in the IBP group displayed NPSVVI compared to 11/44 patients in the TBP group (59 vs. 25 %; p = 0.002, Fisher exact test). When adjusted for gender and lead age, the difference was still significant (p = 0.008). When evaluating the clinical consequence of NPSVVI in this cohort, 3/11 TBP leads with NPSVVI of >0 were eventually extracted due to additional abnormalities vs. 0/26 IBP leads with NPSVVI (p = 0.02, Fisher exact test). None of the IBP group patients with NPSVVI have developed inappropriate therapy from lead noise or a need for abandonment or extraction. Integrated bipolar ICD leads are more likely to have elevated SIC counts than true bipolar leads despite revealing no other evidence of lead failure. There does not appear to be a need for heightened surveillance in IBP leads with observed elevated SIC counts that have no other findings to suggest lead malfunction.

Can we predict and prevent adverse events related to high-voltage implantable cardioverter defibrillator lead failure?

In 2007, great concern arose regarding failure of implantable cardioverter defibrillator (ICD) leads from several manufacturers. Of this analysis was to evaluate the incidence and predictors of Sprint Fidelis lead failure in order to find the best clinical strategy to prevent lead-related adverse events. Four hundred fourteen patients (357 male, 67 ± 12 years) with ICD equipped with right ventricular Sprint Fidelis leads were followed up in our institution. Over a median follow-up of 35 months (25th-75th percentile = 27-47 months) and a total follow-up of 1,231 patient-years, lead failures occurred in 40 of 414 (9.7%) patients. The annual rate was 3.2% per patient-year. Thirty-five (87.5%) failures were caused by pacing-sensing connector fracture. The risk of lead fracture was higher in patients younger than 70 years (odds ratio = 2.31; 95% confidence interval = 1.14-4.68, p = 0.02). Among 30 patients with pacing-sensing conductor failure and available device diagnostics for failure alerting, the diagnostic parameter which first responded to lead failure was the sensing integrity counter in 15 of 30 (50%), pacing impedance in 12 of 30 (40%), and non-sustained ventricular tachycardia in 3 of 30 (10%). The median time (25th-75th percentile) between diagnostics alert and lead failure-related adverse events or failure acknowledgment was 2.2 (0.3-13.0) days. Twenty-two patients suffered inappropriate shocks due to lead failure. In 50% of patients, daily monitoring by device diagnostics would have alerted physicians to impending lead failure at least 1 day in advance. Automatic algorithms based on device diagnostics may detect impending lead failure in nearly 50% of cases. Remote monitoring may prevent failure-related adverse events.

Incidence and Management for Trouble-Shooting Associated with the Sprint-Fidelis ICD Lead

Method: We investigated the outcomes of 136 patients with Sprint-Fidelis in 5 centers in Niigata Prefecture. Results Incidence: Lead troubles occurred in 9 patients (6.6%). The mean period before the trouble was 31 months (16–57 months). Implantation: Among these 9 patients, the lead was implanted using a cut-down technique in 4, an extra-thoracic approach in 4 and a subclavian approach in 1. Discovery: The lead troubles in 5 were discovered at regular clinics. The other 4 patients emergently visited because of the lead integrity alert (LIA) or inappropriate ICD discharges. In the 9 patients, the average sensing integrity counter was 338/day and mean F-F interval, of which was recognized as NST, was less than 200 ms. The LIA: The LIA had been programmed in 7, and 5 of the patients visited before inappropriate ICD discharges. However, the other 2 elderly patients couldn’t notice the alert sound. Extraction: Lead extraction was attempted in 6 and 5 leads were removable without any complications. Conclusions: The incidence of troubles with Sprint-Fidelis is high, and it occurs in the relatively late phase. The LIA is useful to detect the lead problems but its efficacy may be limited in elderly patients.

Causes of ventricular oversensing in implantable cardioverter-defibrillators: Implications for diagnosis of lead fracture

Implantable cardioverter-defibrillator (ICD) ventricular oversensing may result in inappropriate therapy, which may be triggered by lead/connection issues that require surgical revision or physiologic oversensing that may be resolved with reprogramming. The sensing integrity counter (SIC) is an oversensing diagnostic that increments for very rapid ventricular intervals < or =130 ms. The purpose of this study was to determine the causes of a high SIC and the ability of additional diagnostics to differentiate lead/connection issues from other causes of oversensing for patients with normal impedance. Frequent SICs were identified in patients during routine follow-up visits. To diagnose the cause of oversensing, patients wore a modified 24-hour digital Holter monitor that recorded ECG, ventricular electrogram, and the ICD Marker Channel (Medtronic). Recordings were reviewed to determine the causes of oversensing. Patients with confirmed oversensing and adequate data were analyzed. The number of SICs per day and the presence of a nonsustained tachycardia (NST) episode with ventricular mean cycle length <220 ms were retrieved from stored ICD data. Forty-eight patients had a median of 13 SICs/day. Presumed lead/connection issues occurred in 23% of patients, whereas physiologic oversensing occurred in 77% of patients. A rapid NST was recorded more commonly in patients with lead/connection issues than in those without (9/11 vs 1/37; P < .0001). Oversensing resulting in frequent, very short intervals typically are caused by either lead/connection issues or physiologic signals. The additional finding of rapid NSTs usually indicates a lead/connection issue, even in the absence of impedance abnormalities.

High sensing integrity counter in a patient with a Sprint Fidelis defibrillation lead: What is the cause?

The Medtronic Sprint Fidelis implantable cardioverter-defibrillator (ICD) lead has a higher than expected incidence of conductor fractures. Their identification is important to the prevention of inappropriate shocks.1,2 The sensing integrity counter, which stores the cumulative number of nonphysiologically short ventricular intervals ≤130 ms, is a diagnostic feature designed to enhance early identification of lead failures.3 Values greater than 300 are abnormal.

Far-field oversensing of atrial signals: an unusual cause for very short V-V intervals and inappropriate implantable cardioverter defibrillator therapy

A 36-year-old man presented for an unscheduled follow-up after he had experienced multiple shock discharges of his implantable cardioverter defibrillator (ICD) one day earlier while playing soccer. The initial ICD system had been implanted in 1997 for a dilated cardiomyopathy with a left ventricular ejection fraction of 30% and non-sustained ventricular tachycardias (VTs). The current dual-chamber ICD (EnTrustTM, Medtronic Inc., MN, USA) had been implanted in 2004 together with a Medtronic model 5076 atrial lead, whereas the ICD lead (Medtronic Sprint model 6943) had not been replaced since the initial implant in 1997. Several device alert observations were noticed upon device interrogation. First, the sensing integrity counter (SIC), which cumulatively counts very short (120–130 ms) ventricular (V–V) intervals and thereby typically indicates transient oversensing of electrical noise, had increased to 42 552 within the last 3 days. Second, all therapies including shocks had been delivered without success for a VT/ventricular fibrillation (VF) episode. The episode counter showed that eight shocks had been delivered for one VF episode at the …

Failure of impedance monitoring to prevent adverse clinical events caused by fracture of a recalled high-voltage implantable cardioverter-defibrillator lead

The Medtronic Sprint Fidelis implantable cardioverter-defibrillator high-voltage lead is prone to fracture. The October 2007 safety advisory recommended lead impedance monitoring to aid in identifying lead fractures. The aim of this single-center study was to examine the effectiveness of impedance monitoring for detecting Sprint Fidelis lead failures before they caused adverse clinical events such as inappropriate shocks. Impedance and sensing information were acquired during routine clinic and CareLink follow-up and at the time of lead failure using the Patient Alert, sensing integrity counter, nonsustained episode, and electrogram features in Medtronic pulse generators. Between September 2004 and February 2008, 17 of 514 Sprint Fidelis leads (3.3%) followed up at our center failed between 11 and 35 months after implantation (mean 23.0 +/- 8.0 months). Fifteen of these failures (88%) were caused by pace-sense conductor fractures, and 2 (12%) were caused by high-voltage conductor defects. Twelve of 15 patients (80%) with pace-sense conductor fractures received inappropriate shocks; of these, 4 had no significant increase in lead impedance before they were shocked, 2 were shocked <3 hours after their lead impedances exceeded the 1,000 Omega audible alert threshold, and 2 patients did not hear the alarm. All pace-sense conductor failures whose sensing function could be evaluated (13 of 15) had oversensing based on stored data, and oversensing usually (11 of 13) preceded impedances changes. Impedance monitoring did not prevent inappropriate shocks in two-thirds of our patients. Thus, pace-sense conductor impedance monitoring as currently implemented does not reliably forewarn patients of a lead malfunction. Consequently, patients who have Sprint Fidelis leads remain at risk for adverse clinical events associated with pace-sense conductor fracture.

Unusual cause for an increase of the sensing integrity counter in a patient with inappropriate implantable cardioverter-defibrillator therapy

We describe the case of a patient who presented with multiple implantable cardioverter-defibrillator (ICD) shock discharges 12 months after device implantation. Upon device interrogation, intermittent oversensing of electrical noise and potential ICD lead failure were suggested by a significant increase in the sensing integrity counter (SIC), a cumulative count of very short ventricular sensed intervals. Analysis of stored episodes, however, revealed that inappropriate ICD therapy had been caused by intermittent T-wave oversensing (TWO), and that the increase of the SIC resulted from the coincidence of TWO and premature ventricular complexes (PVCs). T-wave oversensing resolved and the SIC did not increase any more during follow-up after adjustment of ventricular sensitivity. The coincidence of TWO and PVCs should therefore be considered as an uncommon cause for short ventricular sensed intervals in ICD patients presenting with a suspect increase in the SIC.

Patient Alert™ to detect ICD lead failure: efficacy, limitations, and implications for future algorithms

An algorithm that alerts implantable cardioverter-defibrillator (ICD) patients, in case of abnormal lead impedance (Patient Alerttrade mark, Medtronic), may help to recognize lead dysfunction. We aimed to determine the utility of Patient Alert for ICD lead-failure detection in a prospective study. Three hundred and sixty ICD patients were followed for 22+/-14 months. Patient Alert was active for pacing impedance <200 and >2000-3000 Omega, and high-voltage conductor impedance <10-20 and >200 Omega. Ten alert events and a total of 29 severe system complications occurred. Patient Alert detected three of 10 ICD lead failures, with a positive predictive value (PPV) of 77.8% for any severe system complication. Retrospective analysis identified 23 patients with a sensing integrity counter (SIC) >300 and revealed an additional four prior undetected lead defects. SIC detected ICD lead failure with 92.9% sensitivity and a PPV of 59.1%. Eight of nine patients with a false-positive SIC had an integrated bipolar lead. Patient Alert combined with SIC detected all ICD lead failures and 71.4% of all severe lead complications. Patient Alert, based on daily lead-impedance measurement, detected one-third of all ICD lead failures. Combined use with continuous lead integrity monitoring (SIC) increased sensitivity to 100%. Integrated bipolar leads may yield a false-positive SIC. Incorporating SIC and automated pace/sense threshold measurement may improve Patient Alert sensitivity for severe lead complications.

Automatic Identification of Clinical Lead Dysfunctions

Implantable cardioverter defibrillators (ICD) lead dysfunctions can cause inappropriate shocks. Current ICDs store lead diagnostics and detected episodes. This stored information with intracardiac electrograms (EGM) and sensed RR interval patterns may characterize the ICD lead performance. The aim of this analysis was to determine the sensitivity and positive predictive value (PPV) of an automatic lead dysfunction identification algorithm. This algorithm uses RR and EGM data to distinguish noncardiac oversensing (OS), for example, due to conductor fracture, and cardiac OS, for example, T-wave OS, from detected episodes. The algorithm also uses lead diagnostics: sensing integrity counter trends (e.g., RR intervals <140 ms), nonsustained tachyarrhythmias episodes with a mean RR <200 ms and impedance trends to identify lead fractures. The PPV was determined using the stored memory from 1,756 ICD patients enrolled in a 13-center long-term lead study with an average follow-up of 18.3 patient-months. Sensitivity was determined in 35 patients who presented with OS or lead fracture-related adverse events confirmed by stored ICD diagnostics. The algorithm sensitivity was 97.1% (34/35). There were 43 additional patients identified by the algorithm without an adverse event. Stored ICD diagnostics confirmed lead dysfunctions in 32 of 43 patients corresponding with an 85.7% PPV (66/77). ICD memory diagnostics and episodes with intracardiac EGM may be used to identify ICD lead dysfunctions with high sensitivity and PPV. This algorithm may be implemented in postprocessing ICD environments (e.g., remote server, programmer) to rapidly identify lead dysfunction prior its clinical manifestation.