Defibrillation energy requirements using a left anterior chest cutaneous to subcutaneous shocking vector:...

Subcutaneous implantable defibrillators (ICDs) are being developed to facilitate ICD implantation.

The purpose of this study was to estimate the human defibrillation energy requirement (DER) using a left chest cutaneous (Q) to subcutaneous (SQ) shocking vector.

Twenty patients undergoing implantation of an indicated ICD were enrolled (15 males, age = 63 +/- 12 years; ejection fraction = 0.27 +/- 0.14). Defibrillation testing was performed using an investigational system consisting of an external defibrillator and a constructed connector to deliver a shock between a pectoral SQ can and a cardiac apical Q electrode. Two attempts at defibrillation using this configuration were allowed. Stage 1 testing started at 70 J with a step-down/step-up to 50 or 100 J, respectively. Stage 2 testing began at 50 J with a step-down/step-up to 30 or 70 J.

During stage 1, a 70-J shock was successful in 7/9 (78%) patients. A second attempt was successful in 7/7 patients using a 50-J shock. In the two remaining patients, a second attempt using a 100-J shock was successful. During stage 2, a 50-J shock was successful in 10/11 (91%) patients. The protocol could not be completed in 2/11 patients. Of the remaining nine patients, a second defibrillation was successful in seven (78%) using a 30-J shock.

The defibrillation energy requirement (DER) of this study vector was 50 J or less in most patients. This low DER supports further investigation of a totally SQ-ICD. However, the DER of 100 J in two patients indicates that further investigation is needed regarding DER variability and safety margins.