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| Electrocardiography |
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| In a hospital, especially in the Intensive care unit (ICU), where seriously ill patients are treated, monitoring of the patients heart rate, blood pressure, temperature, oxygen level in blood etc. is very important. Electronic biomedical equipments continuously monitor the patients vital signs. This helps the doctor to get information about the patients condition, and thus in treatment. |
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| Impulse transmission through the conduction system generates electrical currents that may be detected on the body's surface. A recording of the electrical changes that accompany the cardiac cycle is called an Electrocardiogram (ECG). The instrument used to record the changes is an Electrocardiograph. The simplest type of ECG monitor is a cardio scope. In this, 3 electrodes are connected via a conductive electrolyte gel to the patient for detecting tiny electrical signals. Two electrodes are on the chest above the heart and the third is a connection to the limbs. The modern ECG uses a dozen or more electrodes, placed at 6 different positions on the chest to produce a 3D map of the heart's electrical activity. |
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| ECG can be displayed on a cathode ray tube or for a permanent record on a piece of graph paper. It may be connected to an oscilloscope, which displays it on a TV-type screen. ECG taken when patient is lying down, is called resting ECG, and taken when patient is exercising is called stress ECG. |
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| Each portion of the cardiac cycle produces a different electrical impulse. These impulses are transmitted from the electrodes to a recording pen that graphs the impulses as a series of up and down waves called deflection waves. 3 recognisable waves accompany each cardiac cycle. The first called the P wave, is a small upward wave. It indicates atrial depolarisation - the spread of an impulse from the SA node through the muscle of the two atria. The second wave, called the QRS wave, begins as a downward deflection, continues as a large, upright, triangular wave and ends as a downward wave at its base. This deflection represents ventricular depolarisation, that is, the spread of electrical impulse through the ventricles. The third deflection is a dome shaped T wave. This wave indicates ventricular repolarisation. |
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| The ECG is useful in diagnosing abnormal cardiac rhythms and conduction patterns. It can also detect the presence of foetal life or the presence of several foetuses. ECG reveals the rate of heart beat. It can help diagnose heart disorders following a myocardial infarction, coronary artery diseases etc. |
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