A wearable therapeutic device includes an external defibrillator configured to monitor electrical heart activity of a patient and a garment housing a first therapy electrode and a second therapy electrode. The first and second therapy electrodes are electrically coupled to the defibrillator. The garment releasably receives a plurality of replaceable receptacles configured to store a conductive gel in locations proximate to the therapy electrodes. A plurality of gas cartridges each disposed on one of the plurality of replaceable receptacles are configured to control a release of the stored conductive gel of the associated one of the plurality of replaceable receptacles by igniting. A plurality of conductive gel firing circuits each associated with and separate from each of the plurality of replaceable receptacles are configured to be operatively coupled to the gas cartridge to control the release of the stored conductive gel upon information being communicated from the external defibrillator.
