Final answer:
An ECG is used to assess the heart's electrical activity and detect abnormal rhythms, poor blood flow, and myocardial infarction, while a pulse oximeter is used for measuring oxygen saturation and pulse rate. ECG is more comprehensive for diagnosing heart conditions.
Step-by-step explanation:
An Electrocardiogram (ECG or EKG) is used instead of a pulse oximeter when detailed information about the heart's electrical activity is required. While a pulse oximeter measures the oxygen saturation of the blood and the pulse rate, the ECG provides a comprehensive view of the heart function, detecting abnormal heart rhythms, diagnosing poor blood flow to the heart muscle (ischemia), and observing the effectiveness of heart medications or devices like pacemakers.
ECGs are instrumental in identifying areas of damaged heart tissue, called infarcts, and can indicate subtle changes due to slight or gradual damage to the heart by comparing a recent ECG to an older one. With 12 leads, a state-of-the-art ECG uses 10 electrodes placed in standard locations on the patient's skin, yielding a wealth of information and is especially useful in diagnosing conditions like myocardial infarction (MI) or cardiac arrhythmias.