Air entrapment as a potential cause of early subcutaneous implantable cardioverter defibrillator malfunction: a systematic review of the literature

Noninvasive Impedance Analysis During S-ICD Insertion Provides Justification for Defibrillation Based Testing Deferment

BACKGROUND

Following subcutaneous implantable cardioverter-defibrillator (S-ICD) insertion, induction of ventricular fibrillation (VF) and defibrillation threshold testing (DFT) is the standard of practice to assess system performance. In contrast, DFT testing is not routinely performed after transvenous ICD (T-ICD) insertion, supported by literature that emphasizes negative clinical repercussions and reliability of noninvasive predictors of successful defibrillation. There is a paucity of data for both the trajectory of noninvasive low voltage (LV) impedance measurements at S-ICD insertion through the time of potential DFT testing and for the proximity of LV impedance measurements and high voltage (HV) shock impedance from 65J DFT or 10J testing.

OBJECTIVE

We aim to characterize the trend in LV impedance from initial S-ICD connection (LV T0) to final intraprocedural impedance (LV T4) and to compare LV impedance with HV impedance.

METHODS

Data from patients who underwent S-ICD implantation between July 2022 and March 2024 were analyzed. LV impedance measurements were collected during implant and HV impedance measurements were collected if 65J DFT/10J testing was performed. Differences in mean impedances at each time point were evaluated using paired t-tests. For those who underwent 10J or 65J DFT testing, LV impedance was compared with HV impedance.

RESULTS

The primary analytic sample included 53 patients, with a mean age of 51 ± 15.7 years; 16 (30.2%) were female. LV impedance decreased by a mean of 14.5 ± 9.8 ohms (18.3%; p <0.001) from S-ICD connection (T0) to the final intraprocedural measurement, approximately 60 min postimplant (T4). Among 35 patients who underwent HV testing (65J DFT or 10J), LV impedance at T4 and HV impedance did not differ significantly (1.7 ± 6.3 ohms; p = 0.116).

CONCLUSION

Our findings demonstrate a predictable reduction in LV impedance from S-ICD connection to subsequent intraprocedural measurements. We also found that LV impedance at LV T4, the final intraprocedural measurement, did not significantly differ from contemporaneous HV impedance. Together, these findings indicate that LV impedance at implant can be expected to decline, and that 60-min postimplant LV impedance may reliably approximate HV impedance. Evaluation of circumstances in which LV impedance could influence the decision to perform DFT testing is warranted.

Incidence, implications, and management of sense-B-noise failure in subcutaneous cardioverter-defibrillator patients: insights from a large multicentre registry

AIMS

Subcutaneous implantable cardioverter-defibrillators (S-ICDs) offer potentially distinct advantages over transvenous defibrillator systems. Recent randomized trials showed significantly lower lead failure rates than transvenous ICD. Still, S-ICDs remain associated with the risk of inappropriate shocks (IAS). While previous studies have reported varying causes of IAS, this study explores a rare cause of IAS, referred to as 'sense-B-noise.' It was recently described in case series, but its incidence has not been studied in a large cohort of S-ICD patients.

METHODS AND RESULTS

We retrospectively reviewed data from patients implanted with S-ICD models 1010, A209, and A219 between October 2009 and July 2023 across nine centres in Europe and the USA. The analysis concentrated on determining the incidence and understanding the implications of sense-B-noise events. Sense-B-noise represents a rare manifestation of distinct electrogram abnormalities within the primary and alternate sensing vectors. Data were collected from medical records, device telemetry, and manufacturer reports for investigation. This registry is registered on clinicaltrials.gov (NCT05713708). Subcutaneous implantable cardioverter-defibrillator devices of the 1158 patients were analysed. The median follow-up time for all patients was 46 (IQR 23-64) months. In 107 patients (9.2%) ≥1 IAS was observed during follow-up. Sense-B-noise failure was diagnosed in six (0.5 and 5.6% of all IAS) patients, in all patients, the diagnosis was made after an IAS episode. Median lead dwell time in the affected patients was 23 (2-70) months. To resolve the sense-B-noise defect, in three patients reprogramming to the secondary vector was undertaken, and two patients underwent system removal with subsequent S-ICD reimplantation due to low amplitude in the secondary vector. In one patient, the secondary vector was initially programmed, and subsequently, an S-ICD system exchange was performed due to T-wave-oversensing IAS episodes.

CONCLUSION

This multicentre analysis' findings shed light on a rare but clinically highly significant adverse event in S-ICD therapy. To our knowledge, we provide the first systematic multicentre analysis investigating the incidence of sense-B-noise. Due to being difficult to diagnose and limited options for resolution, management of sense-B-noise is challenging. Complete system exchange may be the only option for some patients. Educating healthcare providers involved in S-ICD patient care is crucial for ensuring accurate diagnosis and effective management of sense-B-noise issues.

Subcutaneous air entrapment after subcutaneous implantable cardioverter defibrillator implantation evaluated by computed tomography

BACKGROUND

Inappropriate shock (IAS) caused by subcutaneous air entrapment (AE) in an early period after subcutaneous implantable cardioverter defibrillator (S-ICD) implantation has been reported, however, no detailed data on air volume are available. We evaluated the subcutaneous air volume after implantation and its absorption rate one week after implantation.

METHODS

Patients who underwent S-ICD implantation in our hospital received chest CT scans immediately after implantation and followed up 1 week later. The total subcutaneous air volume, air around the generator, the distal electrode, and the proximal electrode within 3 cm were calculated using a three-dimensional workstation. Fat areas at the level of the lower edge of the generator were also analyzed.

RESULT

Fifteen patients received CT immediately after implantation. The mean age was 45.6 ± 17.9 (66.7% of men), and the mean body mass index was 24.3 ± 3.3. The three-incision technique was applied in seven patients and two-incision technique was in the latter eight patients. The mean total subcutaneous air volume was 18.54 ± 7.50 mL. Air volume around the generator, the distal electrode, and the proximal electrode were 11.05 ± 5.12, 0.72 ± 0.72, and 0.88 ± 0.87 mL, respectively. Twelve patients received a follow-up CT 1 week later. The mean total subcutaneous air was 0.25 ± 0.45 mL, showing a 98.7% absorption rate.

CONCLUSION

Although subcutaneous air was observed in all patients after S-ICD implantation, most of the air was absorbed within 1 week, suggesting a low occurrence of AE-related IAS after a week postoperation.

Clinical course of hypertrophic cardiomyopathy patients implanted with a transvenous or subcutaneous defibrillator

AIMS

The implantable cardioverter-defibrillator (ICD) is a life-saving therapy in patients with hypertrophic cardiomyopathy (HCM) at risk of sudden cardiac death. Implantable cardioverter-defibrillator complications are of concern. The subcutaneous ICD (S-ICD) does not use transvenous leads and is expected to reduce complications. However, it does not provide bradycardia and anti-tachycardia pacing (ATP). The aim of this study was to compare appropriate and inappropriate ICD interventions, complications, disease-related adverse events and mortality between HCM patients implanted with a S- or transvenous (TV)-ICD.

METHODS AND RESULTS

Consecutive HCM patients implanted with a S- (n = 216) or TV-ICD (n = 211) were enrolled. Propensity-adjusted cumulative Kaplan-Meier curves and multivariate Cox proportional hazard ratios were used to compare 5-year event-free survival and the risk of events. The S-ICD patients had lower 5-year risk of appropriate (HR: 0.32; 95%CI: 0.15-0.65; P = 0.002) and inappropriate (HR: 0.44; 95%CI: 0.20-0.95; P = 0.038) ICD interventions, driven by a high incidence of ATP therapy in the TV-ICD group. The S- and TV-ICD patients experienced similar 5-year rate of device-related complications, albeit the risk of major lead-related complications was lower in S-ICD patients (HR: 0.17; 95%CI: 0.038-0.79; P = 0.023). The TV- and S-ICD patients displayed similar risk of disease-related complications (HR: 0.64; 95%CI: 0.27-1.52; P = 0.309) and mortality (HR: 0.74; 95%CI: 0.29-1.87; P = 0.521).

CONCLUSION

Hypertrophic cardiomyopathy patients implanted with a S-ICD had lower 5-year risk of appropriate and inappropriate ICD therapies as well as of major lead-related complications as compared to those implanted with a TV-ICD. Long-term comparative follow-up studies will clarify whether the lower incidence of major lead-related complications will translate into a morbidity or survival benefit.

S-ICD Implantation "Tips and Tricks"

An implantable cardioverter-defibrillator (ICD) was developed to provide protection against sudden cardiac death. Despite being effective in terminating ventricular arrhythmias, traditional transvenous ICDs appeared over time to have certain limitations related to the need for vascular access and the presence of foreign material inside the circulatory system (namely lead failure and infections). A subcutaneous implantable cardioverter-defibrillator (S-ICD) was developed to overcome those limitations and to provide prevention against sudden cardiac death from outside the cardiovascular system. Utilization of that modern method of treatment is constantly increasing worldwide, and new centers incorporate implantation of that system in their portfolio. This review aims to present the most relevant issues related to S-ICD implantation procedure, based on experience of the authors and an extensive literature search.

Air entrapment as a cause of early inappropriate shocks after subcutaneous defibrillator implant: A case series

Inappropriate shock (IAS) is the most frequent device-related complication among patients with subcutaneous implantable cardioverter-defibrillator (S-ICD). Air entrapment (AE) has been described as an underdiagnosed cause of early postimplant IAS. We report 6 consecutive cases of early IAS after S-ICD implant, in whom the electrogram analysis (EGM) and/or chest radiography (CXR) were consistent with AE.

Sense-B-noise: an enigmatic cause for inappropriate shocks in subcutaneous implantable cardioverter defibrillators

AIMS

Subcutaneous implantable cardioverter defibrillators (S-ICDs) are well established. However, inappropriate shocks (IAS) remain a source of concern since S-ICDs offer very limited troubleshooting options. In our multicentre case series, we describe several patients who experienced IAS due to a previously unknown S-ICD system issue.

METHODS AND RESULTS

We observed six patients suffering from this novel IAS entity. The IAS occurred exclusively in primary or alternate S-ICD sensing vector configuration (therefore called 'Sense-B-noise'). IAS were caused by non-physiologic oversensing episodes characterized by intermittent signal saturation, diminished QRS amplitudes, and disappearance of the artefacts after the IAS. Noise/oversensing could not be provoked by manipulation, X-ray did not show evidence for lead/header issues and impedance measurements were within normal limits. The pooled experience of our centres implies that up to ∼5% of S-ICDs may be affected. The underlying root cause was discussed extensively with the manufacturer but remains unknown and is under further investigation.

CONCLUSION

Sense-B-noise is a novel cause for IAS due to non-physiologic signal oversensing, arising from a previously unknown S-ICD system issue. Sense-B-noise may be suspected if episodes of signal saturation in primary or alternate vector configuration are present, oversensing cannot be provoked, and X-ray and electrical measurements appear normal. The issue can be resolved by reprogramming the device to secondary sensing vector.