Impact of Body Mass Index on Safety and Efficacy of the Subcutaneous Implantable Cardioverter-Defibrillator

Validation of the PRAETORIAN score in a large subcutaneous implantable cardioverter-defibrillator collective: Usefulness in clinical routine

BACKGROUND

To assess the risk of unsuccessful conversion of ventricular fibrillation during defibrillation testing (DFT) with the subcutaneous implantable cardioverter-defibrillator (S-ICD), the PRAETORIAN score has been proposed.

OBJECTIVE

The purpose of this study was to validate the PRAETORIAN score in a large S-ICD collective.

METHODS

A retrospective single-center analysis of S-ICD patients receiving intraoperative DFT was performed. DFT was performed using a stepwise protocol with 65-J standard polarity, change of polarity, increase to 80 J, and repositioning if necessary. If all DFTs failed, we switched to a transvenous ICD.

RESULTS

Overall, 398 patients were analyzed (268 male [67.3%]; mean age 42.4 ± 15.9 years; mean body mass index [BMI] 25.9 ± 4.8 kg/m2). Successful DFT with the first ICD shock was observed in 264 patients (66.3%). One hundred fourteen patients were defibrillated with the second (n = 104) or third (n = 10) DFT after changing shock polarity and/or shock energy. Overall, 20 patients needed at least 3 DFT (ie, 80 J and/or re-positioning). The majority (n = 88 [65.7%]) of DFT failures occurred before 2015 with the first-generation S-ICD. PRAETORIAN score was an independent predictor of DFT failure (odds ratio [OR] 1.007; 95% confidence interval [CI] 1.003-1.011 P ≤.001), while whereas BMI alone was not (P = .31). Presence of hypertrophic cardiomyopathy (HCM) (OR 2.6; 95% CI 1.3-4.4; P = .004) was predictive for at least 1 unsuccessful DFT in our multivariate regression analysis.

CONCLUSION

PRAETORIAN score proved to be a useful and valid predictive tool for successful DFT, whereas BMI only had a limited role. Patients with HCM were at increased risk for DFT failure or needed higher DFT energy.

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.

Successful defibrillation testing in patients undergoing elective subcutaneous implantable cardioverter-defibrillator generator replacement

AIMS

After implantation of a subcutaneous implantable cardioverter-defibrillator (S-ICD), a defibrillation test (DFT) is performed to ensure that the device can effectively detect and terminate the induced ventricular arrhythmia. Data on DFT efficacy at generator replacement are scarce with a limited number of patients and conflicting results. This study evaluates conversion efficacy during DFT at elective S-ICD generator replacement in a large cohort from our tertiary centre.

METHODS AND RESULTS

Retrospective data of patients who underwent an S-ICD generator replacement for battery depletion with subsequent DFT between February 2015 and June 2022 were collected. Defibrillation test data were collected from both implant and replacement procedures. PRAETORIAN scores at implant were calculated. Defibrillation test was defined unsuccessful when two conversions at 65 J failed. A total of 121 patients were included. The defibrillation test was successful in 95% after the first and 98% after two consecutive tests. This was comparable with success rates at implant, despite a significant rise in shock impedance (73 ± 23 vs. 83 ± 24 Ω, P < 0.001). Both patients with an unsuccessful DFT at 65 J successfully converted with 80 J.

CONCLUSION

This study shows a high DFT conversion rate at elective S-ICD generator replacement, which is comparable to conversion rates at implant, despite a rise in shock impedance. Evaluating device position before generator replacement may be recommended to optimize defibrillation success at generator replacement.

Opportunities and drawbacks of the subcutaneous defibrillator across different clinical settings

INTRODUCTION

The subcutaneous implantable cardioverter-defibrillator (S-ICD) is an established therapy for the prevention of sudden cardiac death (SCD) and an alternative to a transvenous implantable cardioverter-defibrillator system in selected patients. Beyond randomized clinical trials, many observational studies have described the clinical performance of S-ICD across different subgroups of patients.

AREAS COVERED

Our review aimed to describe the opportunities and drawbacks of the S-ICD, focusing on their use in special populations and across different clinical settings.

EXPERT OPINION

The choice to implant S-ICD should be based on the patient's tailored approach, which takes into account the adequate S-ICD screening at rest or during stress, the infective risk, the ventricular arrhythmia susceptibility, the progressive nature of the underlying disease, the work or sports activity, and the risk of lead-related complications.

Subcutaneous implantable cardioverter-defibrillator implantation position predicts successful defibrillation in obese and non-obese patients

BACKGROUND

Subcutaneous implantable cardioverter-defibrillators (S-ICD) are an alternative to transvenous ICDs for patients without a need for cardiac pacing. Obese patients have been proposed to be at higher risk for conversion failure with S-ICDs due to subcutaneous fat underneath the device. Optimal device positioning may promote equivalent outcomes between obese and non-obese patients by minimizing the effects of excess adipose tissue.

METHODS

A retrospective analysis of patients undergoing defibrillation testing at the time of S-ICD implantation was performed. The primary endpoint was the rate of successful conversion of ventricular fibrillation (VF) at the time of implant. The secondary endpoint was shock impedance.

RESULTS

A total of 184 patients were included in the study. The rate of successful conversion of VF was 90.3% for obese patients (n = 72) and 96.4% for non-obese patients (n = 112) (p = 0.086). Compared to non-obese patients, obese patients had a higher mean PRAETORIAN score (78.5 ± 58.1 vs. 48.8 ± 35.5, p < 0.001) and higher measured mean impedance (82.0 ohms ± 26.5 vs. 69.8 ohms ± 19.3, p < 0.001). Patients with a PRAETORIAN score < 90 all had successful defibrillation testing regardless of BMI.

CONCLUSIONS

In this study, a PRAETORIAN score < 90 was associated with a 100% success rate of defibrillation testing following S-ICD implantation regardless of patient body mass index (BMI). Thus, the impact of obesity on impedance and the risk of failed shocks may be minimized with close attention to implantation technique to achieve a low PRAETORIAN score.

Pre-implant predictors of inappropriate shocks with the third-generation subcutaneous implantable cardioverter defibrillator

AIMS

Despite recent improvements, inappropriate shocks emitted by implanted subcutaneous implantable cardioverter defibrillators (S-ICDs) remain a challenge in 'real-life' practice. We aimed to study the pre-implant factors associated with inappropriate shocks for the latest generation of S-ICDs.

METHODS AND RESULTS

Three-hundred patients implanted with the third-generation S-ICD system for primary or secondary prevention between January 2017 and March 2020 were included in this multicentre retrospective observational study. A follow-up of at least 6 months and pre-implant screening procedure data were mandatory for inclusion. During a mean follow-up of 22.8 (±11.4) months, 37 patients (12.3%) received appropriate S-ICD shock therapy, whereas 26 patients (8.7%) experienced inappropriate shocks (incidence 4.9 per 100 patient years). The total number of inappropriate shock episodes was 48, with nine patients experiencing multiple episodes. The causes of inappropriate shocks included supraventricular arrhythmias (34.6%) and cardiac (30.7%) or extra-cardiac noise (38.4%) oversensing. Using multivariate analysis, we explored the independent factors associated with inappropriate shocks. These were the availability of less than three sensing vectors during pre-implant screening [hazard ratio (HR), 0.33; 95% confidence interval (CI), 0.11-0.93; P = 0.035], low QRS/T wave ratio in Lead I (for a threshold <3; HR, 4.79; 95% CI, 2.00-11.49; P < 0.001), history of supraventricular tachycardia (HR, 8.67; 95% CI, 2.80-26.7; P < 0.001), and being overweight (body mass index > 25; HR, 2.66; 95% CI, 1.10-6.45; P = 0.03).

CONCLUSION

Automatic pre-implant screening data are a useful quantitative predictor of inappropriate shocks. Electrocardiogram features should be taken into consideration along with other clinical factors to identify patients at high risk of inappropriate shocks.

A 10 J shock impedance in sinus rhythm correlates with a 65 J defibrillation impedance during subcutaneous defibrillator implantation using an intermuscular technique

INTRODUCTION

Defibrillation testing (DT) is recommended during the subcutaneous defibrillator (S-ICD) placement. We sought to compare 10 J shock impedance in sinus rhythm (SR) with 65 J defibrillation impedance and evaluate device position on a postimplant chest X-ray (CXR) using an intermuscular (IM) technique.

METHODS

Consecutive S-ICD implantations between 12/2019 and 12/2020 at The Ohio State University were reviewed. All implantations were performed using a two-incision IM technique. Standard DT with 65 J shock and 10 J shock in SR were performed unless contraindicated. The PRAETORIAN score was calculated based on CXR.

RESULTS

A total of 37 patients (age: 47.2 ± 15.8 years old, male: n = 26 [70.3%], body mass index: 30.1 ± 6.7 kg/m² ) underwent IM S-ICD implantation, and of those, 27 (73%) underwent both 65 J shock and 10 J shock in SR. The coefficient of determination (R² ) between 10 J shock impedance and 65 J shock impedance was 0.84. The mean of an impedance difference was 1.6 ± 4.8 Ω (minimum - 11 and maximum 8). Postimplant CXR was available for 33 out of 37 patients (89.2%). The PRAETORIAN score was less than 90 in all patients and the mean score was 32.7 ± 8.8.

CONCLUSION

We demonstrated that 10 J shock impedance in SR correlated well with 65 J defibrillation impedance during IM S-ICD implantation. An IM implantation technique provides excellent generator location on postimplant CXR. The IM technique combined with 10 J shock in SR may be sufficient to predict and ensure the defibrillation efficacy of the S-ICD.

The extravascular implantable cardioverter-defibrillator: The pivotal study plan

Background

Transvenous implantable cardioverter defibrillators (TV ICD) provide life‐saving therapy for millions of patients worldwide. However, they are susceptible to several potential short‐ and long‐ term complications including cardiac perforation and pneumothorax, lead dislodgement, venous obstruction, and infection. The extravascular ICD system's novel design and substernal implant approach avoids the risks associated with TV ICDs while still providing pacing features and similar generator size to TV ICDs.

Study Design

The EV ICD pivotal study is a prospective, multicenter, single‐arm, nonrandomized, premarket clinical study designed to examine the safety and acute efficacy of the system. This study will enroll up to 400 patients with a Class I or IIa indication for implantation of an ICD. Implanted subjects will be followed up to approximately 3.5 years, depending on when the patient is enrolled.

Objective

The clinical trial is designed to demonstrate safety and effectiveness of the EV ICD system in human use. The safety endpoint is freedom from major complications, while the efficacy endpoint is defibrillation success. Both endpoints will be assessed against prespecified criteria. Additionally, this study will evaluate antitachycardia pacing performance, electrical performance, extracardiac pacing sensation, asystole pacing, appropriate and inappropriate shocks, as well as a summary of adverse events.

Conclusion

The EV ICD pivotal study is designed to provide clear evidence addressing the safety and efficacy performance of the EV ICD System.

Long-term complications in patients implanted with subcutaneous implantable cardioverter-defibrillators: Real-world data from the extended ELISIR experience

BACKGROUND

Recently, the Food and Drug Administration issued a recall for the subcutaneous implantable cardioverter-defibrillator (S-ICD) because of the possibility of lead ruptures and accelerated battery depletion.

OBJECTIVE

The aim of this study was to evaluate device-related complications over time in a large real-world multicenter S-ICD cohort.

METHODS

Patients implanted with an S-ICD from January 2015 to June 2020 were enrolled from a 19-institution European registry (Experience from the Long-term Italian S-ICD registry [ELISIR]; ClinicalTrials.gov identifier NCT0473876). Device-related complication rates over follow-up were collected. Last follow-up of patients was performed after the Boston Scientific recall issue.

RESULTS

A total of 1254 patients (median age 52.0 [interquartile range 41.0-62.2] years; 973 (77.6%) men; 387 (30.9%) ischemic) was enrolled. Over a follow-up of 23.2 (12.8-37.8) months, complications were observed in 117 patients (9.3%) for a total of 127 device-related complications (23.6% managed conservatively and 76.4% required reintervention). Twenty-seven patients (2.2%) had unanticipated generator replacement after 3.6 (3.3-3.9) years, while 4 (0.3%) had lead rupture. Body mass index (hazard ratio [HR] 1.063 [95% confidence interval 1.028-1.100]; P < .001), chronic kidney disease (HR 1.960 [1.191-3.225]; P = .008), and oral anticoagulation (HR 1.437 [1.010-2.045]; P = .043) were associated with an increase in overall complications, whereas older age (HR 0.980 [0.967-0.994]; P = .007) and procedure performed in high-volume centers (HR 0.463 [0.300-0.715]; P = .001) were protective factors.

CONCLUSION

The overall complication rate over 23.2 months of follow-up in a multicenter S-ICD cohort was 9.3%. Early unanticipated device battery depletions occurred in 2.2% of patients, while lead fracture was observed in 0.3%, which is in line with the expected rates reported by Boston Scientific.

Subcutaneous implantable cardioverter defibrillator: Can it overtake its transvenous counterpart

Over the past decade, the emergence of the subcutaneous implantable cardioverter defibrillator (S-ICD) has provided cardiologists with an option to provide both primary or secondary prevention treatment of sudden cardiac death (SCD) without the associated risks that come with the use of intracardiac leads. S-ICD may prove to be a useful option in those who are young, have thromboembolic risk, immunodeficiency states, unfavorable anatomy due to adult congenital heart disease (ACHD). This article reviews the existing literature to determine whether S-ICD can prove to be a safe alternative in comparison to Transvenous implantable cardioverter defibrillator (TV-ICD) and in which patient population should S-ICD be considered over TV-ICD.

Acute shock efficacy of the subcutaneous implantable cardioverter-defibrillator according to the implantation technique

BACKGROUND

The traditional technique for subcutaneous implantable cardioverter defibrillator (S-ICD) implantation involves three incisions and a subcutaneous (SC) pocket. An intermuscular (IM) 2-incision technique has been recently adopted.

AIMS

We assessed acute defibrillation efficacy (DE) of S-ICD (DE ≤65 J) according to the implantation technique.

METHODS

We analyzed consecutive patients who underwent S-ICD implantation and DE testing at 53 Italian centers. Regression analysis was used to determine the association between DFT and implantation technique.

RESULTS

A total of 805 patients were enrolled. Four groups were assessed: IM + 2 incisions (n = 546), SC + 2 incisions (n = 133), SC + 3 incisions (n = 111), and IM + 3 incisions (n = 15). DE was ≤65 J in 782 (97.1%) patients. Patients with DE ≤65 J showed a trend towards lower body mass index (25.1 vs. 26.5; p = .12), were less frequently on antiarrhythmic drugs (13% vs. 26%; p = .06) and more commonly underwent implantation with the 2-incision technique (85% vs. 70%; p = .04). The IM + 2-incision technique showed the lowest defibrillation failure rate (2.2%) and shock impedance (66 Ohm, interquartile range: 57-77). On multivariate analysis, the 2-incision technique was associated with a lower incidence of shock failure (hazard ratio: 0.305; 95% confidence interval: 0.102-0.907; p = .033). Shock impedance was lower with the IM than with the SC approach (66 vs. 70 Ohm p = .002) and with the 2-incision than the 3-incision technique (67 vs. 72 Ohm; p = .006).

CONCLUSIONS

In a large population of S-ICD patients, we observed a high defibrillation success rate. The IM + 2-incision technique provides lower shock impedance and a higher likelihood of successful defibrillation.

Defibrillation testing during implantation of the subcutaneous implantable cardioverter-defibrillator: a necessary standard or becoming redundant?

Since the publication of the SIMPLE and NORDIC trials, defibrillation testing (DFT) is rarely performed during routine implantation of transvenous implantable cardioverter-defibrillators (ICD). However, the results of these trials cannot be extrapolated to the later introduced subcutaneous ICD (S-ICD) and a class I recommendation to perform DFT during the implantation of these devices remains in the current guidelines. Due to the high conversion success rate of DFT on one hand, and the risk of complications on the other, a significant number of physicians omit DFT in S‑ICD recipients. Several retrospective analyses have assessed the safety of the omission of DFT and report contradicting results and recommendations. It is known that implant position, as well as device factors and patient characteristics, influence defibrillation success. A better comprehension of these factors and their relationship could lead to more reliable and safer alternatives to DFT. An ongoing randomised clinical trial, which is expected to end in 2023, is the first study to implement a method that assesses implant position to identify patients who are likely to fail their DFT.

Approaches to Minimizing Periprocedural Complications During Subcutaneous Implantable Cardioverter-defibrillator Placement

The subcutaneous implantable cardioverter-defibrillator (S-ICD) is the latest option among devices clinically available for the prevention of sudden cardiac death, with experience from previous trials and postmarketing studies supporting the feasibility and safety of this kind of system. The extracardiac positioning of the S-ICD obviates the need for transvenous leads, which translates into lower incidence rates of lead-related complications and systemic infections. This review will highlight the results of pertinent studies related to the perioperative management of S-ICDs and review potential approaches to minimizing the risk of complications such as hematoma at the pulse generator location, unsuccessful defibrillation due to suboptimal S-ICD lead and generator positioning, and postoperative pain. An extensive literature search using PubMed was conducted to identify relevant articles.

Refractoriness to subcutaneous implantable cardioverter defibrillator after frequent therapies for ventricular fibrillation storms in a Brugada syndrome case

Background

The subcutaneous implantable cardioverter defibrillator (S-ICD) is an alternative to the transvenous implantable cardioverter defibrillator for the prevention of sudden cardiac death. Here, we report a rare case of refractoriness to an S-ICD after frequent therapies for ventricular fibrillation (VF) storms.

Case presentation

A 24-year-old man underwent a bout of syncope with vomiting and incontinence at home. He was brought to the emergency room and was witnessed to spontaneously go into VF successfully converted by external defibrillation. Previously, he was diagnosed with a type I Brugada electrocardiogram pattern by a pilsicainide administration test in another hospital. Although he had a family history of sudden cardiac death in 3 relatives, including his brother, he was followed closely without any therapies because he had never had an episode of syncope. He was implanted with an S-ICD without any trouble. Seven months later, frequent S-ICD shocks for VF storms occurred. His VF was controlled by using intravenous amiodarone, which was converted to an oral preparation. However, his VF recurred after another 2 months. The analysis of his S-ICD data revealed that 4 consecutive shock deliveries could not terminate his VF and the final shock delivered could fortunately terminate it because of a high defibrillation threshold test (DFT) due to an increasing shock impedance (64 to 90 Ω). First, we performed an epicardial Brugada syndrome ablation and subsequently replaced and repositioned the S-ICD lead from a left to a right parasternal site. After the re-implantation of the S-ICD, the DFT test improved to within normal range. According to the pathological analysis, infiltration of inflammatory cells and extensive fibrosis were confirmed in the subcutaneous tissue around the shock lead and S-ICD body.

Conclusion

Frequent S-ICD shocks for VF storms might cause various pathological changes around the device and lead to a high DFT.

The subcutaneous implantable cardioverter-defibrillator in review

The subcutaneous implantable cardioverter defibrillator (S-ICD) is a completely extrathoracic device that has recently been FDA approved for the prevention of sudden cardiac death in select populations. Although the transvenous implantable cardioverter defibrillator (TV-ICD) has a proven mortality benefit in multiple patient populations, there are significant risks both with implantation and years after its placement. The S-ICD may help prevent some of these complications. Currently, the S-ICD is typically implanted in patients with prior device infection or at an increased risk for an infection, younger patients with difficult venous access related to either hemodialysis or difficult cardiac anatomy, patients who live active lifestyles, and those who may outlive the TV-ICD leads. There is an absolute contraindication for S-ICD implantations for patients who need pacing either for ventricular tachycardia or bradycardia because this device cannot perform these functions. To date, there are no randomized controlled trial (RCT) data evaluating the safety and efficacy of this relatively new device. Observational studies of both the S-ICD alone and in comparison with the TV-ICD have showed promising results, including a decrease in lead-related and periprocedural complications as well as a high level of effectiveness at terminating ventricular arrhythmias. These analyses over time may have contributed to the evolution and comfortability with the S-ICD system, as physicians are more often referring for and/or implanting this device for patients with appropriate indications. Furthermore, inappropriate shock rates with the S-ICD have decreased over time especially with dual zone programming. This review summarizes the results of a multitude of observational studies with respect to patient selection for the S-ICD, complication rates, appropriate and inappropriate shock rates, and programming. This review also tackles current ongoing randomized trials. Although the results of ongoing trials will be helpful, there is still a continued need to evaluate the efficacy of the S-ICD in broader patient populations including patients with several comorbidities and older patients so that more patients can be considered for this potentially lifesaving device.

Ventricular Fibrillation Refractory to Cutaneous Electrical Defibrillation in a Morbidly Obese Pediatric Patient With Hypertrophic Cardiomyopathy: A Case Report

We report a case of subcutaneous implantable cardioverter-defibrillator implantation in a morbidly obese pediatric patient with hypertrophic cardiomyopathy for the primary prevention of sudden cardiac death. During routine defibrillator threshold testing of the newly placed subcutaneous implantable cardioverter defibrillator, normal sinus rhythm could not be restored despite repeated attempts at defibrillation using the subcutaneous implantable cardioverter defibrillator and transcutaneous pads. Here, we describe the successful intraoperative resuscitation and management after failure to restore normal sinus rhythm using the newly placed subcutaneous implantable cardioverter defibrillator and repeated transcutaneous defibrillation attempts.

Efficacy, safety, and in-hospital outcomes of subcutaneous versus transvenous implantable defibrillator therapy: A meta-analysis and systematic review

BACKGROUND

Lead-related complication is an important drawback of trans-venous implantable cardioverter-defibrillators (TV-ICD). The subcutaneous ICD (S-ICD) was developed to overcome ICD lead associated complications; however, whether the S-ICD confers enhanced clinical benefits compared with TV-ICD remains unclear. The present systematic review and meta-analysis aimed to assess TV-ICD and S-ICD for safety, efficacy, and in-hospital outcomes in the prevention of sudden cardiac death (SCD) in patients not requiring pacing.

METHODS

The Medline, PubMed, EmBase, and Cochrane Library databases were searched for studies comparing TV-ICD and S-ICD.

RESULTS

A total of 9 eligible studies, including 5 propensity-matched case-control, 3 retrospective, and 1 cross-sectional studies were identified, assessing 7361 patients in all. Pool analyses demonstrated that SICD were associated with lower lead-related complication rates [odds ratio (OR) = 0.13; 95% confidence interval [CI] 0.05-0.33; I = 0%], and S-ICD was more beneficial in terms of reducing ICD shocks [OR = 0.48; 95% CI 0.32-0.72, I = 4%]. In addition, the patients administered S-ICD tend to have shorter length of hospital stay after implantation (SMD = -0.06; 95% CI -0.11 to 0.00, I = 0%) and reduce total complication rates (OR = 0.72; 95% CI 0.50-1.03; I = 18%), non-decreased quality of life (QoL). Moreover, both devices appeared to perform equally well with respect to infection rate and death.

CONCLUSIONS

Available overall data suggested that S-ICD is associated with reducing lead-related complications, ICD shocks. In addition, S-ICD has tendency to shorten hospitalization and reduce total complications, although the difference is no significant. Equivalent death rate, infection, and QoL were found between 2 groups. Therefore, S-ICD could be considered an alternative approach to TV-ICD in appropriate patients for SCD prevention.

A novel tool to evaluate the implant position and predict defibrillation success of the subcutaneous implantable cardioverter-defibrillator: The PRAETORIAN score

BACKGROUND

Suboptimal positioning of the subcutaneous implantable cardioverter-defibrillator (S-ICD) increases the defibrillation threshold and risk of conversion failure.

OBJECTIVE

Our objective is to develop a tool to evaluate the implant position and predict defibrillation success of the S-ICD: the PRAETORIAN score.

METHODS

The PRAETORIAN score is based on clinical and computer modeling knowledge of determinants affecting the defibrillation threshold: subcoil fat, subgenerator fat, and anterior positioning of the S-ICD generator. The score evaluates these determinants on the postoperative anterior-posterior and lateral chest radiographs and has 3 categories: 30-<90 points representing a low risk, 90-<150 points representing an intermediate risk, and ≥150 points representing a high risk of conversion failure. The score was developed using 2 separate S-ICD data sets for derivation and validation. The performance metrics are the positive and negative predictive values.

RESULTS

The development data set consisted of 181 patients with S-ICD, and the validation cohort consisted of 321 patients from the S-ICD Investigational Device Exemption trial. The distribution of scores was 93%-98% low risk (<90 points), 2%-5% intermediate risk (90-<150 points), and 1% high risk (≥150 points). The positive predictive value for an intermediate or high PRAETORIAN score for a failed conversion test was 51%, while a low PRAETORIAN score predicted a successful conversion in 99.8% of patients.

CONCLUSION

The PRAETORIAN score allows the identification of patients with high defibrillation thresholds by using the routine chest radiograph and provides feedback to implanters on S-ICD positioning. The PRAETORIAN-DFT trial will prospectively validate the score by randomizing to standard conversion testing vs using the score without conversion testing.

Defibrillation Threshold Testing: Current Status

When the transvenous ICD initially came into use for primary and secondary prevention of sudden cardiac death, defibrillation threshold (DFT) testing was universally performed. However, DFT testing is no longer routinely recommended for transvenous ICD implantation except in certain situations. Risk scores can help guide the decision to perform DFT testing. The subcutaneous ICD represents an area of uncertainty, with limited data available regarding the role of DFT testing in these devices. Current guidelines give a class I recommendation for performing DFT testing at the time of implant. Further studies are needed before this recommendation can be safely dismissed.