An ECG records the rate, rhythm and electrical currents of a patient's heartbeat. When any of these measurements show abnormal activity, the doctor uses that information to help determine what type of heart problem the patient is experiencing, according to eMedicineHealth. However, the ECG is only part of the diagnostic process and doctors rely on other information in addition to the ECG data in order to evaluate a patient properly.
An ECG recording uses 12 leads: six on the chest and six on the limbs, explains eMedicineHealth. The electrical currents appear in the form of a wave pattern known as the P-QRS-T wave. Each letter stands for a different section of the heart and how electricity flows through it during a normal heartbeat rhythm. An abnormal heartbeat or unusual electrical activity causes the wave pattern to shift out of its normal position, and the type of shift can indicate what sort of heart trouble the patient is having.
It is possible for an ECG reading to appear normal when in fact the patient is experiencing heart trouble, says eMedicineHealth. Likewise, an abnormal ECG make actually be the norm for a particular patient. Because of this, doctors also consider the patient's medical history, current condition and other factors as part of their overall assessment.