An electrocardiogram taken at a routine follow-up in a Chinese hospital showed something that should not have been possible. Two distinct QRS morphologies, meaning two different electrical signatures of a heartbeat, were appearing in the same tracing. The patient's heart was being paced by two devices at once.
Only one of them was supposed to be switched on. The other was an older single-chamber pacemaker, deliberately disabled during a 2018 upgrade and left inside the chest. It had turned itself back on.
