In electrocardiography (ECG) system, a patient cable connecting one or more electrodes to a processing device for processing ECG signals may include one or more electrode connectors mechanically keyed to respective electrodes and/or a device connector mechanically and/or electronically keyed to a cable connector of the processing device. In some embodiments, keying between the cable and electrode is achieved, for example, with an electrode including a hollow-post portion that defines a bore in conjunction with a post protruding from an arm of the electrode connector that is sized to fit within the bore.