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

doi:10.1016/j.hrthm.2018.09.029

Heart Rhythm

Volume 16, Issue 3, March 2019, Pages 403-410

https://doi.org/10.1016/j.hrthm.2018.09.029 Get rights and content

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.

Introduction

The subcutaneous implantable cardioverter-defibrillator (S-ICD) has emerged as an alternative to transvenous implantable cardioverter-defibrillators in an effort to reduce lead-related complications.1, 2, 3, 4 The extrathoracic position requires adequate positioning of both the lead and the generator to ensure that the myocardium is exposed to sufficient electric current to defibrillate.

Both computer modeling and clinical experience have identified 3 critical implant position determinants that cause an increase in defibrillation threshold (DFT): (1) adipose tissue between the coil and the sternum; (2) generator malposition along the anterior-posterior (AP) axis; and (3) adipose tissue between the generator and the thorax.5, 6, 7 Adipose tissue has insulating properties causing resistance to the electrical circuit and therefore a reduction in the effective current, while a too anterior generator position causes the current to shunt via the anterior chest wall instead of traversing the critical mass of the heart.⁷

Periprocedural conversion testing is currently recommended to ensure adequate device functioning, but provides limited information because of the probabilistic nature of conversion testing.8, 9 Biphasic waveform shocks have a conversion efficacy of ∼90% when sufficient volts/cm resets the effective refractory period of the majority of the myocardium.¹⁰ To establish the actual DFT for the individual patient and reduce the probabilistic effect of conversion testing would require testing with multiple shocks during testing, which is clinically undesirable.

Considering the importance of device positioning, the limitations of conversion testing, and the ability to evaluate position on the routine postoperative chest radiograph, we sought to develop an evaluation tool that provides both actionable feedback on implant quality and identifies implanted patients at risk of a high DFT without the need for conversion testing. The objectives of this study were to report the development of, and provide retrospective validation results, of this tool, the PRAETORIAN score, and to compare its value with previously suggested predictors of shock efficacy.

Section snippets

Development of the PRAETORIAN score

The PRAETORIAN score was designed as a noninvasive scoring method that uses the routine postprocedural chest radiograph so that it is easy to implement in the current clinical workflow. The score quantifies 3 components of the S-ICD implant position, which have been shown to be critical determinants of the DFT, both in anecdotal clinical experience and in computer modeling studies (Figure 1).5, 7, 11, 12

The PRAETORIAN score consists of 3 steps: The first step assesses the amount of adipose

AMC cohort

The development and initial validation data sets scored by 3 independent physicians consisted of a single-center cohort of 181 patients. All patients were implanted by 1 experienced implanter between 2009 and 2017. The majority of these patients had primary prevention indication (67%), a mean left ventricular ejection fraction of 50%, and a mean age of 41.4 ± 16.9 years. Two patients had a high (>150) PRAETORIAN score; one of these failed the conversion test (Table 1). No patients with a low

Main findings

This study introduces a noninvasive tool correlating S-ICD implant position to shock efficacy during acute conversion testing. The ultimate goal of the PRAETORIAN score is to identify patients at high risk of conversion failure as well as to predict shock efficacy in spontaneous events without having to perform a conversion test. In addition, the PRAETORIAN score provides feedback on which element of the implant contributes to the increased risk of conversion failure. Retrospective assessment

Conclusion

The PRAETORIAN score is a noninvasive method to evaluate the S-ICD implant position and predict the chance of successful conversion testing with better predictive values than previously published predictors such as impedance. The score provides actionable feedback on how to improve implantation technique and solve high DFT issues.

References (22)

L. Boersma et al.
Implant and midterm outcomes of the subcutaneous implantable cardioverter-defibrillator registry: the EFFORTLESS Study
J Am Coll Cardiol
(2017)
T.F. Brouwer et al.
Long-term clinical outcomes of subcutaneous versus transvenous implantable defibrillator therapy
J Am Coll Cardiol
(2016)
M.C. Burke et al.
Safety and efficacy of the totally subcutaneous implantable defibrillator: 2-year results from a pooled analysis of the IDE Study and EFFORTLESS Registry
J Am Coll Cardiol
(2015)
H. Sugumar et al.
Subcutaneous ICD lead position affects defibrillation threshold
HeartRhythm Case Rep
(2018)
E.K. Heist et al.
Determinants of subcutaneous implantable cardioverter-defibrillator efficacy: a computer modeling study
JACC Clin Electrophysiol
(2017)
S.M. Al-Khatib et al.
2017 AHA/ACC/HRS guideline for management of patients with ventricular arrhythmias and the prevention of sudden cardiac death: executive summary: a report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines and the Heart Rhythm Society
Heart Rhythm
(2018)
D.S. Frankel et al.
Impact of body mass index on safety and efficacy of the subcutaneous implantable cardioverter-defibrillator
JACC Clin Electrophysiol
(2018)
H.E. Saltzman et al.
Increased shock impedance is associated with failed subcutaneous implantable cardioverter defibrillator defibrillation threshold testing
J Am Coll Cardiol
(2017)
M.A. Miller et al.
Subcutaneous implantable cardioverter-defibrillator implantation without defibrillation testing
J Am Coll Cardiol
(2017)
N. Maurizi et al.
Effectiveness of subcutaneous implantable cardioverter-defibrillator testing in patients with hypertrophic cardiomyopathy
Int J Cardiol
(2017)

G.H. Bardy et al.

An entirely subcutaneous implantable cardioverter-defibrillator

N Engl J Med

(2010)

Cited by (95)

Differences in underlying cardiac substrate among S-ICD recipients and its impact on long-term device-related outcomes: Real-world insights from the iSUSI registry
2024, Heart Rhythm
Outcome comparisons among subcutaneous implantable cardioverter-defibrillator (S-ICD) recipients with nonischemic cardiomyopathies are scarce.
The aim of this study was to evaluate differences in device-related outcomes among S-ICD recipients with different structural substrates.
Patients enrolled in the i-SUSI (International SUbcutaneouS Implantable cardioverter defibrillator registry) project were grouped according to the underlying substrate (ischemic vs nonischemic) and subgrouped into dilated cardiomyopathy, hypertrophic cardiomyopathy, Brugada syndrome (BrS), arrhythmogenic right ventricular cardiomyopathy (ARVC). The main outcome of our study was to compare the rates of appropriate and inappropriate shocks and device-related complications.
Among 1698 patients, the most common underlying substrate was ischemic (31.7%), followed by dilated cardiomyopathy (20.5%), BrS (10.8%), hypertrophic cardiomyopathy (8.5%), and ARVC (4.4%). S-ICD for primary prevention was more common in the nonischemic cohort (70.9% vs 65.4%; P = .037). Over a median (interquartile range) follow-up of 26.5 (12.6–42.8) months, no differences were observed in appropriate shocks between ischemic and nonischemic patients (4.8%/y vs 3.9%/y; log-rank, P = .282). ARVC (9.0%/y; hazard ratio [HR] 2.492; P = .001) and BrS (1.8%/y; HR 0.396; P = .008) constituted the groups with the highest and lowest rates of appropriate shocks, respectively. Device-related complications did not differ between groups (ischemic: 6.4%/y vs nonischemic: 6.1%/y; log-rank, P = .666), nor among underlying substrates (log-rank, P = .089). Nonischemic patients experienced higher rates of inappropriate shocks than did ischemic S-ICD recipients (4.4%/y vs 3.0%/y; log-rank, P = .043), with patients with ARVC (9.9%/y; P = .001) having the highest risk, even after controlling for confounders (adjusted HR 2.243; confidence interval 1.338–4.267; P = .002).
Most S-ICD recipients were primary prevention nonischemic cardiomyopathy patients. Among those, patients with ARVC tend to receive the most frequent appropriate and inappropriate shocks and patients with BrS the least frequent appropriate shocks.
Defibrillation threshold in elective subcutaneous implantable defibrillator generator replacements: Time to reduce the size of the pulse generator?
2024, International Journal of Cardiology
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.
We aimed to find the DFT in patients undergoing S-ICD generator replacement.
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.
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.
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.
Humerus fracture during unsuccessful induction of ventricular fibrillation for subcutaneous implantable cardioverter-defibrillator testing
2024, HeartRhythm Case Reports
Validation of the PRAETORIAN score in a large subcutaneous implantable cardioverter-defibrillator collective: Usefulness in clinical routine
2024, Heart Rhythm
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.
The purpose of this study was to validate the PRAETORIAN score in a large S-ICD collective.
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.
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.
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.
Predictive value of the PRAETORIAN score for defibrillation test success in patients with subcutaneous ICD: A subanalysis of the PRAETORIAN-DFT trial
2024, Heart Rhythm
The PRAETORIAN score estimates the risk of failure of subcutaneous implantable cardioverter-defibrillator (S-ICD) therapy by using generator and lead positioning on bidirectional chest radiographs. The PRospective randomized compArative trial of subcutanEous implanTable cardiOverter-defibrillatoR ImplANtation with and without DeFibrillation Testing (PRAETORIAN-DFT) investigates whether PRAETORIAN score calculation is noninferior to defibrillation testing (DFT) with regard to first shock efficacy in spontaneous events.
This prespecified subanalysis assessed the predictive value of the PRAETORIAN score for defibrillation success in induced ventricular arrhythmias.
This multicenter investigator-initiated trial randomized 965 patients between DFT and PRAETORIAN score calculation after de novo S-ICD implantation. Successful DFT was defined as conversion of induced ventricular arrhythmia in <5 seconds from shock delivery within 2 attempts. Bidirectional chest radiographs were obtained after implantation. The predictive value of the PRAETORIAN score for DFT success was calculated for patients in the DFT arm.
In total, 482 patients were randomized to undergo DFT. Of these patients, 457 (95%) underwent DFT according to protocol, of whom 445 (97%) had successful DFT and 12 (3%) had failed DFT. A PRAETORIAN score of ≥90 had a positive predictive value of 25% for failed DFT, and a PRAETORIAN score of <90 had a negative predictive value of 99% for successful DFT. A PRAETORIAN score of ≥90 was the strongest independent predictor for failed DFT (odds ratio 33.77; confidence interval 6.13–279.95; P < .001).
A PRAETORIAN score of <90 serves as a reliable indicator for DFT success in patients with S-ICD, and a PRAETORIAN score of ≥90 is a strong predictor for DFT failure.
Subcutaneous Implantable Cardioverter Defibrillators in Pediatrics and Congenital Heart Disease
2023, Cardiac Electrophysiology Clinics

View all citing articles on Scopus

: Dr Brouwer has received research grant and compensation for services from Boston Scientific. Dr Burke has received compensation for services from Boston Scientific. Dr Wilde has received compensation for services from LivaNova. Dr Knops has received research grants from Boston Scientific, Medtronic, and Abbott. The rest of the authors report no conflicts of interest.

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

Background

Objective

Methods

Results

Conclusion

Introduction

Section snippets

Development of the PRAETORIAN score

AMC cohort

Main findings

Conclusion

J Am Coll Cardiol

J Am Coll Cardiol

J Am Coll Cardiol

HeartRhythm Case Rep

JACC Clin Electrophysiol

Heart Rhythm

JACC Clin Electrophysiol

J Am Coll Cardiol

J Am Coll Cardiol

Int J Cardiol

An entirely subcutaneous implantable cardioverter-defibrillator

N Engl J Med

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