A wearable cardioverter defibrillator (“WCD”) system may include an impedance detector configured to render an impedance signal of the patient. The WCD system may determine, from the impedance signal, a characteristic of breathing by the patient that can be used as a vital sign. The WCD system may determine, from at least the breathing characteristic, whether or not a shock criterion is met. If the shock criterion is met, the WCD system may control a discharge circuit to discharge a stored electrical charge through the patient. An advantage can be that the breathing characteristic may be used to determine whether or not a patient is experiencing a condition that requires defibrillation therapy, such as sudden cardiac arrest. Even more advantages can be had in discerning the state of the patient when the breathing characteristic is combined with other data, such as from a motion detector.