It's not an ECG per se, because an ECG would have 15 or so different leads that get placed all over the patient's body in order to get a reading.
But there's this thingy... it's like an ECG, but there's only 3 leads and it goes into the cardiac monitor screen. There's a red wire, a black wire, and a white wire, so "smoke over fire, white is right" is used to place this thing's leads.
