Precise Measurement of Pediatric Defibrillation Thresholds

Study Overview
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Brief Summary
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Patients who receive an implantable cardioverter-defibrillator (ICD) usually undergo testing at the end of the ICD procedure to measure the amount of energy able to successfully defibrillate the heart (defibrillation threshold testing, or DFT). This study proposes to perform that measurement in pediatric patients already undergoing clinically necessary ICD procedures, with the measurement performed using a binary search method that has been previously validated in adult cohorts. We hypothesize that pediatric DFTs, when precisely measured, may be lower than previously assumed from extrapolation of adult data.

Official Title
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Defibrillation Thresholds in a Pediatric Cohort Using Binary Search Protocol

Conditions
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Pediatrics, Defibrillators, Implantable

Intervention / Treatment
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* Diagnostic Test: Defibrillator threshold testing
* Other: Observation of post-shock intrinsic cardiac rhythm


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Current follow-up at Children's Hospital Boston Children with current or planned ICDs who are scheduled by their primary electrophysiologist for clinically necessary assessment/re-assessment of defibrillation threshold If the patient has an ICD system with a non-transvenous shock coil: weight ≤35kg at time of initial implant, with current weight <50kg If the patient has an ICD system with a conventional transvenous shock coil: current weight ≤60kg Exclusion Criteria: Clinical failure of any system component not able to be addressed by hardware repair or exchange Hemodynamic instability that in the judgment of the primary electrophysiologist warrants abbreviation of DFT assessment Unsuccessful induction of fibrillation during DFT testing
Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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No

Study Plan
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How is the study designed?
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Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Pediatric ICD pts<br>Inclusion criteria for study participants included: 1) weight ≤60 kg, 2) new or existing ICD system, and 3) clinically necessary assessment of the defibrillation efficacy of the ICD system. Transvenous systems utilized a high-voltage ICD coil with active-fixation lead attached to the right ventricular endocardial surface, whereas non-transvenous systems depended upon a high-voltage shocking coil placed within the pericardial, subcutaneous or pleural space. To be included in the post-shock pacing portion of the study, adequate sinus and AV node function had to be present at baseline. Exclusion criteria included 1) tenuous hemodynamic status felt to warrant abbreviation of the defibrillation efficacy testing or 2) inability to induce fibrillation during defibrillation threshold testing (DFT). | Diagnostic Test: Defibrillator threshold testing<br>* Measurement of the defibrillation threshold was performed using a modified binary search protocol. This protocol specified three distinct inductions of ventricular fibrillation (VF) for all subjects, with a 3-5 minute observation/waiting period between inductions. The initial shock energy was programmed at 9 joules (J) for all patients, with internal rescue shocks at 31J followed by device-specific maximum deliverable energy. The outcome of the initial induction determined the programmed energies for both the initial and internal rescue shocks for the second induction, and likewise for the third induction. All shocks were biphasic and delivered at manufacturers' default tilt, polarity and duration, and all final programmed shock vectors included an active can. External defibrillation pads were in place for delivery of external rescue shock should the internal shocks fail.<br>Other: Observation of post-shock intrinsic cardiac rhythm<br>* Prior to each of the three ventricular fibrillation inductions performed as part of the binary search protocol, post-shock pacing was re-programmed using a pre-determined, stepwise protocol that progressively decreased the lower rate limit. For the purpose of this protocol, post-shock pacing was considered necessary if 1) ≥7 ventricular-paced beats or 2) asystole >4 seconds was observed in the first 20 seconds after defibrillation, or if the systolic blood pressure demonstrated a >10% decrease from pre-induction baseline at follow-up measurement 1 minute post-defibrillation. Rescue ventricular pacing via the programmer was available for all subjects.<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Defibrillation Threshold | The defibrillation threshold is a measure of the minimum amount of energy (in Joules) that is able to successfully defibrillate an episode of ventricular fibrillation. This measurement is specific to each individual patient with his/her specific defibrillator configuration. There are several different strategies to measuring this in an individual patient; this study utilized the binary search protocol. | During clinical ICD procedure, as a single event | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Do DFTs Vary by Type of ICD Systems Implanted? | The defibrillation threshold (as measured in Joules as already described in the details regarding the primary outcome) will be compared between patients with two distinct general types of implanted defibrillator systems: 1) transvenous ICD systems (defibrillator leads located inside the vein and attached to the endocardial surface of the heart) and 2) non-transvenous ICD systems (including all other types of debrillation systems). | During clinical ICD procedure, as a single event | 
| Intrinsic Heart Rate in the Immediate Post-defibrillation Period | A patient will be considered to have an intrinsic slow heart rate in the period of time immediately following defibrillation (20 seconds) if any of the following are observed: >7 paced beats, asystole >4 seconds, or experienced >10% decrease in systolic blood pressure. | During clinical ICD procedure, as a single event |