A cardiac monitoring and treatment system includes a controller, a first wearable portion, and a second wearable portion separate from the first wearable portion. The first wearable portion includes an elongated strap configured to encircle a thoracic region of a patient, a plurality of ECG sensing electrodes disposed about the elongated strap, one or more receiving ports configured to receive one or more additional components including a treatment electrode and/or an additional sensor, and a plurality of conductive wires configured to couple the plurality of ECG sensing electrodes and the one or more receiving ports with the controller. The second wearable portion is configured to be worn over at least one shoulder of the patient and includes a wearable substrate, one or more treatment electrodes disposed on the wearable substrate, and at least one conductive wire configured to releasably connect the one or more treatment electrodes to the controller.