131-04: Novel Extravascular Defibrillation Configuration with a Coil in the Substernal Space

Abstract

Purpose: Subcutaneous (SQ) ICDs are regarded as alternatives to transvenous (TV) ICDs in certain patients (pts). However, a substantially higher shock energy up to 80J may be required primarily because both the parasternal shock coil and lateral ICD can are outside the rib cage. Proposed is a new defibrillation method of placing the shock coil into the space immediately behind the sternum. This study assessed the defibrillation efficacy of the substernal-lateral electrode configuration. Method: This prospective, non-randomized, feasibility study was conducted in pts about to undergo midline sternotomy or implant of a SQ or TV ICD. A tunneling tool (6996T, Medtronic) was used to insert an 8 cm coil defibrillation lead (6937, Medtronic) behind the sternum using a percutaneous sub-xiphoid approach under fluoroscopic guidance. A skin patch electrode (Fast Patch Plus, Physio Control) was placed on the left thorax at the 4th to 5th intercostal space. After ventricular fibrillation (VF) induction, a single 35J shock was delivered between the substernal coil and the left lateral patch using an external TV ICD (Protecta, Medtronic), with external rescue shock if needed. Summary of Results: Sixteen pts (12 males, 4 females; mean age: 61.6 ± 11.8 years; BMI: 25.6 ± 3.3; LVEF: 47 ± 18%) were enrolled at 5 sites in Europe and Hong Kong. Ten studies preceded sternotomy (2 coronary bypass grafting; 7 valve repair/replacement; 1 aortic aneurysm repair) and 6 preceded ICD implants (5 SQ and 1 TV). All were under general anesthesia except 4 out of 5 SQ ICD pts which were under conscious sedation. Mean lead placement time was 11.1 ± 6.6 minutes. Of the 14 pts with successfully induced VF episodes, 13 pts (92.9%) had successful defibrillation at 35J. The one failure was associated with high and lateral shock coil placement, and one external rescue shock was successful. Mean VF duration was 18.4 ± 5.6 seconds with shock impedance of 98.1 ± 19.3 ohms. Of the 11 pts with coil-patch electrograms, the average R-wave amplitude during normal sinus rhythm was 3.0 ± 1.4 mV. Conclusion: These preliminary data demonstrate that substernal defibrillation is feasible and that successful defibrillation can be achieved with the shock energy available in current TV ICDs. This may open new alternatives to TV ICD therapy.