The ECG is rarely entirely normal in CPO, although there are no diagnostic features specific to CPO.
It will often show a tachycardia and possible left ventricular hypertrophy.
It may reveal precipitating causes such as ST segment changes associated with an ACS (STEMI or NSTEMI) or an arrhythmia eg atrial fibrillation.
Look at these examples of ECGs. Click each example to see a larger version: