Medical
Biology
White Blood Cells WBC and Red Blood Cells RBC
Question
Which of the following correctly explains a phase / event in cardiac cycle in a standard electrocardiogram ?
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Solution
Electrocardiogram (ECG), is a graphical representation of the electrical activity of the heart during a cardiac cycle. The machine used to obtain an electrocardiogram is known as an electrocardiograph.
A normal electrogram (ECG) is composed of a P wave, a QRS wave (complex), and a T wave.
QRS complex represents ventricular depolarization that lead to ventricular contraction.
It is caused by the impulses from the AV node through the bundle of His and Purkinje fibres.
Thus this wave (QRS) is due to the spread of electrical impulse through the ventricles.
The S-T interval represents the time between the end of the spread of impulse through ventricles and its repolarization.
The P wave is a small upward wave that represents atrial depolarisation which leads to contraction of both the atria (atrial contraction).
It is caused by the activation of the SA node. The impulses of contraction start from the SA node and spread throughout the atria.
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