Electrocardiogram(ECG) is a tool that is used to measure and record the electrical activity of the heart. An Electrocardiogram is necessary to establish many heart related defects like atrial enlargement, ventricular hypertrophy(enlargement of the ventricles),arrhythmias(abnormal electrical activity of the heart) and conditions that may lead to sudden death.
The term Electrocardiogram was coined by Willem Einthoven in the year 1893. He was awarded Nobel Prize for his work in developing Electrocardiogram.
The test is simple, painless and risk free. The patient is asked to lie down on an examination table. 10 electrodes are attached to the body (arms, legs and chest). With the help of the electrodes, electrical signals generated by the heart are transmitted to the ECG machine. A graph is produced by the machine. The electrodes are removed after the graph of the cardiac electrical signals is obtained.
Electrical rhythm as an impulse is emitted from the sinoatrial node (heart’s natural pacemaker). The impulse then travels across a specific route through the upper heart chambers causing them to contract in unison. The impulse then reaches the atrioventricular(AV) node which is between the upper and lower chambers of the heart. The impulse is reorganized before being transmitted to the ventricle along special bundle of electrical conducting tissue. Once the impulse reaches the ventricles, it causes the chambers to contract in a consistent manner. If the impulse send is delayed or send through a wrong route, the heartbeat may be irregular. These are detected on the ECG.
The P wave represents the electrical impulse traveling across the atria of the heart. Abnormalities in this region hence reflect the presence of any kind of abnormality in the left or right atrial region.
The QRS complex represents electrical impulse across the Ventricles. An abnormality in this region is noticed mainly in cases of heart attack, were the muscles of the ventricle are damaged.
The T wave represents recovery period of a ventricle muscle after it is stimulated. An abnormality in this region is noticed when there is improper availability of oxygen in the heart.
Region in the graph between the QRS complex and T wave is known as the ST segment. Abnormalities in this region are noticed due to a blockage in any of the valves.
Thus from an ECG, information on Heart rate, its rhythm, where is the defect, and if there is abnormal thickening of the heart muscles. If a heart attack is inferred from the graph, further tests are carried out. If thickening of the heart muscle is found, an echocardiogram or Ultra Sound is taken to find out other structural abnormalities.