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