ECG Tutorial   

 

Introduction
       Electrode Placement
Anatomy
Heart Rate
PR Interval
QRS Interval
QT Interval

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Theoretical Basis of the ECG
An electrical current in the direction towards the positive end of a bipolar electrode causes a positive deflection of the stylus of the ECG. If the number of myocardial cells (dipoles) in this direction increases, the current will increase as well. The greater the current, the more positive the voltage. An electrical current in the direction away from the positive end of a bipolar electrode causes a negative deflection of the stylus of the ECG. If the number of myocardial cells (dipoles) in this direction increases, the current will increase as well.  The greater the current, the more negative the voltage.

ECG Leads
An electrocardiographic lead is a recording electrode or a pair of recording electrodes at a specified location. In clinical practice, twelve leads are usually used in the diagnostic ECG, although there is no limitation to the number of leads one may select for special purposes. The leads are usually placed on the elbows and stifles. A right leg electrode is used as the ground.

ECG Standard Leads
Leads I, II and III are all bipolar (i.e., they detect a change in electric potential between two points) and detect an electrical potential change in the frontal plane. Lead I is between the right arm and left arm electrodes, the left arm being positive. Lead II is between the right arm and left leg electrodes, the left leg being positive. Lead III is between the left arm and left leg electrodes, the left leg again being positive.


Copyright 1999 University of Pennsylvania School of Veterinary Medicine
Faculty Sponsor: Dr. Virginia Reef
Student: Jeff Horst  V'02
Date this page was last updated: May 20, 2002