Purpose of ECG Test
ECG is used to
- Detect bradycardia and tachycardia.
- Determine if symptoms, such as chest pain, shortness of breath or palpitations are due to a heart problem.
- Know steady or irregular heart rhythm.
- Know the strength and timing of electrical signals as they pass through each part of your heart
- Detect other disorders that affect heart function.
- Study and detect many heart problems, such as heart attacks, arrhythmia, heart failure.
- Assess coronary blood flow and heart valves integrity.
- Monitor deeply-sedated patients and for consciously-sedated patients with compromised cardiovascular function.
- Monitor some medications for the heart.
- The indications for exercise electrocardiography include to ascertain the correct exercise prescription, the investigation of angina and post-myocardial infarction assessment as well as the postoperative examination of bypass surgery.
Electrode and Lead
An electrode is a sensor (conductive pad) attached to the skin and enables recording of electrical currents. An ECG lead is a graphical description of the electrical activity of the heart created by reading several electrodes. This means that each ECG lead is gotten by analysing the electrical currents detected by several electrodes. A 12-lead ECG is obtained using 10 electrodes. These 12 leads consists of limb leads and chest leads (percordial leads). For further reading see...
To better under why there are only 10 leads instead of 12 leads read about Einthoven's triangle and the heart's action potential generation.
The ECG paper is a strip of graph paper with large and small grids with horizontal axis (Time in seconds) and vertical axis(amplitude in volts). Each 1 mm square (the smallest square) represents 0.04 second and each large square (5 mm) represents 0.2 second. On the vertical axis, each large square represents 0.5mV and each small block equals 0.1mV.