Subcutaneous Array (Endotak SQ Model 0048) Notes

Electrode system with three conductive elements ("Lead Array") inserted subcutaneously.
Developed to replace the SQ patch in most configurations, acting as an anode or part of the anode.
Depolarizes a greater cardiac surface area compared to the SQ patch (51 cm² vs. 28 cm²).
Conductive elements: electrically common multifilar coil.
Three elements (25 cm length, 6 French diameter) joined in a silicone yoke connected to a terminal pin.
Each leg is introduced separately using a lead tunneler and peel-away sheaths.

3 cm incision to position the yoke.
Lead elements introduced with three separate sheaths after tunneling to the left lateral part of the chest using a dilator.
Elements are individually sutured after sheath removal.
Fluoroscopy is used during implantation.
(A) Initial lead position - may show failing shocks.
(B) After dispersion of array branches, the patient can be defibrillated with biphasic bi-directional shocks of 10 J.

Illustrate typical location for Endotak and SQ Array leads.
Postero-anterior radiograph (left panel): distal array leads extend posteriorly in subcutaneous tissue of the chest wall.
Leads inserted through incision at approximately the mid-clavicular line anteriorly.
Lateral view (right panel): three SQ Array lead elements splayed but paralleling the ribs.

SQ Array results were superior to lead-alone configurations, but DFT reduction wasn't universal.
20% of patients had identical DFT with lead-alone and lead-SQ Array.
5% of patients had lower DFT with lead-alone intraoperatively; postoperatively, lead-alone was incapable of successful defibrillation.

2001 report: Subcutaneous arrays in right and left chest walls showed good defibrillation thresholds in a 2-year-old with ventricular tachycardia and repaired congenital heart disease.
Other reports: ICD implantation in a child using a single subcutaneous array lead and an abdominal active can via an ileofemoral approach.

Major concern: potential for lead trauma and damage with alternative techniques.
Superficially placed leads (not under rib cage) are exposed to external trauma.

6% of patients with subcutaneous array had a major complication, the most common being lead fracture (approximately 4%).
An additional 6% had minor lead insulation defects that might affect future performance and cause serious complications.
Children are more prone to falls and blunt trauma, potentially damaging superficially placed leads.