The EKG Waveform

Introduction

The SA node spontaneously depolarize to initiate an action impulse that is rapidly propagated through the atria (causing atrial contract), then slowly through the AV node and rapidly via the bundle branches and Purkinje system to the ventricles, causing ventricular contraction. 

The electrical activity of the heart can be recorded at the surface of the body using an electrocardiogram. The electrocardiogram (EKG) is simply a voltmeter that uses up to 12 different leads (electrodes) placed on  designated areas of the body.

The electrocardiogram is composed of waves and complexes. Waves and complexes in the normal sinus rhythm are the P wave, PR Interval, PR Segment, QRS Complex, ST Segment, QT Interval and T wave (shown below). 

Click here for an animation of the normal sinus rhythm from the P wave to T wave.  You will need shockwave.

·        The P wave is caused by atrial depolarization.  The P wave is usually smooth and positive. The P wave duration is normally less than 0.12 sec. More...

·        The PR interval is the portion of the EKG wave from the beginning of the P wave ( onset of atrial depolarization) to the beginning of the QRS complex ( onset of ventricular depolarization). It is normally  0.12 - 0.20 seconds. More...

·     The PR segment is the portion on the EKG wave from the end of the P wave to the beginning of the QRS complex. The PR segment corresponds to the time between the end of atrial depolarization to the onset of ventricular depolarization. It  is an isoelectric segment, during which the impulse travels from the AV node through the conducting tissue (bundle branches, and Purkinje fibers) towards the ventricles. More...

·        The QRS complex represents the time it takes for depolarization of the ventricles. - due to ventricular depolarization. The normal QRS interval range is from 0.04 sec - 0.12 sec measured from the first deflection to the end of the QRS complex. More...

·     The ST Segment represents the period of ventricular muscle contraction before repolarization. The ST segment is normally isoelectric (no electrical activity is recorded). however, the ventricles are contracting. More...

·        The QT interval begins at the onset of the QRS complex and to the end of the T wave. It represents the time of ventricular depolarization until ventricular repolarization. More...

·         The T wave due to ventricular repolarization The wave is normally rounded and positive. More...

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