Defibrillation threshold in elective subcutaneous implantable defibrillator generator replacements: Time to reduce the size of the pulse generator?

INTRODUCTION

The first step-down defibrillation studies in the subcutaneous implantable cardioverter-defibrillator (S-ICD) described a defibrillation threshold (DFT) of 32.5 ± 17.0 J and 36.6 ± 19.8 J. Therefore, the default shock output of the S-ICD was set at 80 J. In de novo implants, the DFT is lower in optimally positioned S-ICDs. However, a retrospective analysis raised concerns about a high DFT in S-ICD replacements, possibly related to fibrosis.

OBJECTIVE

We aimed to find the DFT in patients undergoing S-ICD generator replacement.

METHODS

This prospective study enrolled patients who underwent S-ICD generator replacement with subsequent defibrillation testing. A pre-specified defibrillation testing protocol was used to determine the DFT, defined as the lowest shock output that effectively terminated the induced ventricular arrhythmia.

RESULTS

A total of 45 patients were enrolled, 6.0 ± 2.1 years after initial implant. Mean DFT during replacement in the total cohort was 27.4 ± 14.3 J. In patients with a body mass index (BMI) 18.5-25 kg/m2 (N = 22, BMI 22.5 ± 1.6), median DFT was 20 J (IQR 17.5-30). In 18/22 patients, the DFT was ≤30 J and 5/22 patients were successfully defibrillated at 10 J. One patient with hypertrophic cardiomyopathy had a DFT of 65 J. In patients with a BMI >25 kg/m2 (N = 23, BMI 29.5 ± 4.2), median DFT was 30 J (IQR 20-40). In 15/23 patients, the DFT was ≤30 J and 4/23 patients had a successful defibrillation test at 10 J.

CONCLUSIONS

This study eases concerns about a high DFT after S-ICD generator replacement. The majority of patients had a DFT ≤30 J, regardless of BMI, suggesting that the shock output of the S-ICD could be safely reduced.

Clinical relevance of the single-lead ECG of the Apple Watch

Introduction

The Apple Watch (AW) is one of the first commercially available wearable with built-in electrocardiogram (ECG) electrodes to perform a single-lead ECG to detect atrial fibrillation (AF). The AW ECG application showed to have a high rate of unclassifiable notifications. The interpretation of the single-lead ECG by a physician can possibly reduce the total of unclassifiable notifications and contribute to the overall accuracy to detect AF.

Methods

This was a prospective, non-randomized, single center observational study to evaluate the accuracy and interrater agreement of the single-lead ECG of the AW. Patients scheduled for cardioversion for atrial fibrillation were asked for participation. The AW series 6 was used with WatchiOS 7.2 or 7.3 and ECG algorithm version 2.0. A single-lead ECG was obtained pre-conversion and, when cardioversion was successful, post-conversion. All single-lead ECGs and 12-lead ECGs were adjudicated by two physicians, agreement was reached by consensus. The AW single-lead ECG notification was compared to the physicians “gold-standard” interpretation of the 12-lead ECG. Sensitivity and specificity of the AW single-lead ECG and Kappa coefficient were calculated.

Results

In total, 74 patients were included. Mean age was 67.1±12.3 years and 20.3% were female. In total 65 AF and 64 sinus rhythm (SR) single-lead ECG measurements were obtained. Of these measurements, 27.9% (36/129) showed an unclassifiable notification. The AW ECG notification showed a sensitivity of 93.5% to detect AF and a specificity of 100% to detect SR (K= 0.94). After adjudication of the unclassifiable notifications by two independent physicians 1.6% (2/129) of the measurements remained unclassifiable. When including the by the physicians adjudicated unclassifiable recordings the sensitivity to diagnose AF was 89.2% and the specificity to detect SR was 93.8% (K=0.83). The adjudication of all single-lead ECGs by the two physicians showed a sensitivity of 90.6% to detect AF and specificity of 95.2% to detect SR (K= 0.83) (Table 1). All SR and AF notification by the AW were similarly adjudicated by the two physicians. The kappa coefficient for interrater agreement between both physicians was 0.69 for all single-lead ECGs and 0.58 for unclassifiable notifications specific.

Conclusion

Unclassifiable notifications of the AW can be reduced by physicians interpretation of the single-lead ECG, however the interrater agreement is only moderate. The physicians interpretation of the single-lead ECGs did not increase the accuracy to detect AF and the clinical relevance of the single-lead ECG, in addition to the AW notification, should therefore be questioned.

Funding Acknowledgement

Type of funding sources: None.

Mechanism, follow-up and recurrence of inappropriate therapy in the PRAETORIAN trial: action reduces recurrence

Funding Acknowledgements

Type of funding sources: Private company. Main funding source(s): Boston Scientific Corporation

Background

The PRAETORIAN trial demonstrated that the subcutaneous ICD (S-ICD) is non-inferior to the transvenous ICD (TV-ICD) with regard to inappropriate shocks (IAS) and complications. Inappropriate therapy is an undesirable side effect of ICD therapy.

Purpose

This pre-specified secondary analysis evaluates all inappropriate therapy in the PRAETORIAN trial and subsequent action to reduce recurrence of IAS.

Methods

The PRAETORIAN trial is an international, multicentre, randomised trial, which included patients with an indication for ICD therapy. In total, 849 patients were randomised to receive an S-ICD (N=426) or TV-ICD (N=423). ICD programming was mandated by protocol. Inappropriate therapy was defined as any ICD therapy on a different rhythm than ventricular tachycardia or ventricular fibrillation. A day with inappropriate therapy was defined as all device episodes on the same day. Mechanism, actions and recurrence rate were determined using days with inappropriate therapy.

Results

In the S-ICD group, 42/426 (10%) patients received inappropriate therapy, compared to 42/423 (10%) patients in the TV-ICD group (P=0.97). In total, 41 patients in the S-ICD and 29 patients in the TV-ICD group received at least one IAS (P=0.14). The total number of IAS in the S-ICD and TV-ICD group is comparable (124 vs. 130, P=0.88). The most common underlying mechanism of inappropriate therapy was T-wave oversensing in the S-ICD group (45%) and a supraventricular tachycardia (SVT) in a therapy zone in the TV-ICD group (93%). When no action was undertaken after the first IAS, the recurrence rate of an IAS of the same etiology was 56% (5/9) in the S-ICD group and 50% (4/8) in the TV-ICD group. An action, such as a change in medication, a change in programming, an invasive action or lifestyle advise resulted in a recurrence rate of 23% (7/30) in the S-ICD group and 30% (6/20) in the TV-ICD group. The recurrence rate was significantly higher when no action was undertaken versus any action (P=0.04) (Figure 1.). A change in programming resulted in a lower recurrence rate than a change in medication (S-ICD, 40% vs. 27% and TV-ICD, 44% vs. 17%). After an invasive action no recurrence of IAS occurred in both groups. Invasive actions were more common in the S-ICD group (7/41, vs. 1/29). In the S-ICD group the most common action was a change in programming (17/41), mainly when the underlying mechanism of IAS was cardiac oversensing. In the TV-ICD group the most common action was a change in medication (12/29), mainly and only when the underlying mechanism of IAS was an SVT (Figure 2.).

Conclusion

The total number of IAS and total patients receiving IAS are not statistically different between the S-ICD group and the TV-ICD group. However, the underlying mechanism and action after IAS differ and are associated with the different sensing of the ICDs. The recurrence rate after a first IAS was significantly higher when no action was undertaken.

Reasons for replacement and extraction of the subcutaneous implantable cardioverter-defibrillator in a large cohort

Funding Acknowledgements

Type of funding sources: None.

Background

The subcutaneous implantable cardioverter-defibrillator (S-ICD) is proven to be a safe and effective alternative to the transvenous ICD. However, battery longevity is estimated to be shorter in the S-ICD, although newer generations S-ICD are thought to have an increased battery longevity compared to the first generation. In addition, the S-ICD lacks the option for pacing therapy and may therefore be extracted in patients who later develop an indication for bradycardia pacing, antitachycardia pacing or resynchronization therapy. In this analysis, we aim to evaluate occurrence and reasons for S-ICD replacement and extraction.

Methods

In this retrospective analysis, we collected data on S-ICD generator replacement and extraction from consecutive patients who were implanted with an S-ICD in our tertiary center between February 2009 and December 2021.

Results

A total of 408 patients received an S-ICD, with a median follow-up duration of 4.0 (IQR 1.5-6.8) years. Of the 168 implanted first generation S-ICDs, 123 (73.2%) were replaced after a mean of 5.9 ± 0.8 years, all due to battery depletion. A second generation S-ICD was replaced in 2/40 (5%) patients and a third generation S-ICD in 11/200 patients (5.5%), after a mean of 4.8 ± 0.12 and 3.6 ± 1.6 years, respectively. Two third generation S-ICDs were replaced due to device malfunction, all other replacements (134/136, 98.5%) were due to battery depletion. The S-ICD was extracted in 38/408 (9.3%) patients. The mean time from initial implantation to extraction was 3.7 ± 2.5 years. Reasons for extraction were a newly developed indication for pacing or resynchronization therapy (N = 14), an expired indication for ICD therapy (N = 8), heart transplantation or implantation of left ventricular assist device (N = 4), repeated inappropriate shocks (N = 4), pocket infection (N = 3), pocket erosion (N = 2), lead defect (N = 1), Twiddler syndrome (N = 1) and patient preference (N = 1). A new S-ICD could be re-implanted in 7 patients (18.4%), a cardiac resynchronization therapy defibrillator was implanted in 7 patients (18.4%) and there was a need for a transvenous ICD in 10 patients (26.3%). The remaining 14 patients (36.8%) were not re-implanted with any type of ICD. Reasons for end of S-ICD therapy are presented in the figure.

Conclusion

In this large cohort, a battery longevity of the first generation S-ICD of 5.9 years was reached. After a median follow-up duration of 4.0 years, 17/408 patients received a transvenous device, due to the need for bradycardia or antitachycardia pacing or resynchronization therapy. Importantly, 14/408 patients underwent an S-ICD extraction and were not re-implanted with any type of ICD. These patients may especially benefit from S-ICD therapy, as this device is less complicated to extract compared to a transvenous ICD.

Defibrillation success after subcutaneous implantable cardioverter-defibrillator generator replacement is not affected by impedance increase

Funding Acknowledgements

Type of funding sources: None.

Background

Routine defibrillation testing during implant and replacement of the subcutaneous implantable cardioverter-defibrillator (S-ICD) is recommended per current guidelines. Recently, concerns have been raised about an increase in shock impedance and consequent shock failure during defibrillation testing in S-ICD patients undergoing a generator replacement.

Purpose

We aim to describe the defibrillation success rate in relation to the shock impedance in patients undergoing S-ICD generator replacement in our large tertiary center.

Methods

In this retrospective analysis, data from replacement procedures were collected from all patients who underwent an S-ICD generator replacement in our center from June 2014 to December 2020. Defibrillation testing was performed with at least one shock of ≤65J, and a successful shock was defined as terminating the ventricular arrhythmia within 5 seconds after the shock.

Results

A total of 133 patients underwent an S-ICD generator replacement, 5.8 ± 0.9 years after initial implant. Reasons for replacement were: reaching of elective replacement indicator (n = 119), early battery depletion (n = 9), complaints of generator pocket (n = 3) and device malfunction (n = 2). Defibrillation testing was performed in 111 patients (86.5%) undergoing a replacement procedure. Shock impedance data from both the implant and replacement procedure were available in 101 patients. The median shock impedance of these patients during their replacement procedure was significantly higher than during their implant, 79Ω (IQR 66-94) and 66Ω (IQR 57.5-81) respectively (Z = -5.552, p < 0.001). Despite the higher shock impedance, first shock during defibrillation testing was successful in 105/111 patients (94.6%), with a success rate of 97.3% after two attempts. In the remaining three patients, the ventricular arrhythmia could only be terminated with a 80J shock. This was the case during both their initial implant and their replacement procedure. Shock impedance increase between implant and replacement was not significantly higher in patients with a successful first shock compared to patients with an unsuccessful first shock (Δ+11.1 ± 20.0Ω versus Δ+12.7 ± 27.6Ω, p = 0.86).

Conclusion

In this large retrospective analysis, we have shown a first shock success rate during S-ICD generator replacement of 94.6%, which is similar to the success rate of defibrillation testing after initial implant. After multiple attempts, defibrillation testing success rate was 100%. Even though the median shock impedance during replacement was significantly higher than during the initial implant, there was no difference in impedance increase in patients with a successful shock compared to patients with an unsuccessful shock. Abstract Figure. Defibrillation success

Dual Site-Specific Chemoenzymatic Antibody Fragment Conjugation Using CRISPR-Based Hybridoma Engineering

Functionalized antibodies and antibody fragments have found applications in the fields of biomedical imaging, theranostics, and antibody–drug conjugates (ADC). In addition, therapeutic and theranostic approaches benefit from the possibility to deliver more than one type of cargo to target cells, further challenging stochastic labeling strategies. Thus, bioconjugation methods to reproducibly obtain defined homogeneous conjugates bearing multiple different cargo molecules, without compromising target affinity, are in demand. Here, we describe a straightforward CRISPR/Cas9-based strategy to rapidly engineer hybridoma cells to secrete Fab′ fragments bearing two distinct site-specific labeling motifs, which can be separately modified by two different sortase A mutants. We show that sequential genetic editing of the heavy chain (HC) and light chain (LC) loci enables the generation of a stable cell line that secretes a dual tagged Fab′ molecule (DTFab′), which can be easily isolated. To demonstrate feasibility, we functionalized the DTFab′ with two distinct cargos in a site-specific manner. This technology platform will be valuable in the development of multimodal imaging agents, theranostics, and next-generation ADCs.

Clinical implications of heart-lung interactions

As opposed to spontaneous respiration wherein small cyclic changes in transpulmonary, negative pressure coincide with lung volume changes, positive pressure (mechanical) ventilation results in a simultaneous rise in transpulmonary pressure and lung volumes. The changes may affect biventricular cardiac loading and function in dissimilar ways, depending on baseline cardiopulmonary function. This review is intended to update current knowledge on the pathophysiology of these heart-lung interactions in helping to explain the common circulatory alterations occurring during airway pressure changes and to better understand mechanisms of disease and modes of action of treatments, during spontaneous and mechanical ventilation.