Electrocardiography (ECG) Procedure Explained

ECG (Electrocardiography)

Electrocardiography is a recording of the electrical activity of the heart from the body surface. It is done by using sensitive electrodes placed on standard positions on the chest and limbs and recording the activity on a special graphical paper. Normal ECG has certain features. But every normal ECG is not identical. There are wide ranges of normalcy. So two ECGs appearing to be different to a layman’s eyes, could be normal. Likewise, all abnormal ECGs do not necessarily indicate serious problems. In spite of limitations, ECG remains an easily accessible, simple and useful initial investigation. In expert’s hands, it is a very valuable tool and can detect variety of conditions.

One of the commonest uses of ECG is to detect ischaemia (reduced blood supply) to heart muscles. During Angina (chest pain) or Myocardial infarction (heart attack), ECG will show typical charges which are diagnostic.

Stress ECG or Treadmill Test (TMT) is a method of recording ECG while the subject is exercising (alternatively, heart can be stressed by some drugs like dobutamine). Stress or exercise will uncover some ischaemia that is not obvious while at rest. A strongly positive TMT mostly indicate blocks in the coronary arteries. But a negative TMT does not completely rule out blocks (Negative predictive value is about 75%).

Holter ECG is a continuous recording of ECG for 24 hours or more using a portable device. This may be helpful in picking up transient rhythm disturbances or ischaemia which would otherwise escape detection during standard ECG.