RESUMO
INTRODUCTION: This study reports the experimental process leading to development of an automatic totally subcutaneous implantable cardioverter defibrillator (SICD) system engineered for human use. METHODS AND RESULTS: Two studies were conducted to test defibrillation and detection feasibility of an SICD system located in the left chest. In the first study, 2 pockets were created in 15 canines for placement of an anterior electrode adjacent to the left edge of the sternum and a lateral electrode at the site along the axillary line between the 4th and 6th intercostal space. Stainless steel flat electrodes with active surface areas of 5, 10, 20, and 25 cm(2) or rod electrodes were subsequently positioned and the defibrillation threshold (DFT) was measured for multiple combinations. In the second study, the ability to induce, detect, and provide shock delivery in response to ventricular fibrillation (VF) using an SICD system engineered for clinical use was tested in 5 canines. One hundred and three DFT tests with 11 different dual electrode combinations were performed. All combinations terminated VF with a DFT of 35 ± 16 J (range: 9-79 J). Nineteen VF episodes were induced and recognized by the chronic SICD, leading to automatic capacitor charge and shock delivery in all cases. CONCLUSIONS: Subcutaneous defibrillation using different electrode combinations with shock energies less than 80 J terminated all induced VFs. An automatic SICD proved effective in detecting and activating shock delivery in all cases.