As the heart undergoes depolarization and repolarization , the electrical currents that are generated spread not only within the heart, ut also throughout the ody! This electrical activity generated y the heart is generally measured y an array of electrodes placed on the ody surface and the resulting tracing is called an electrocardiogram "#C$, or #%$&! The different waves that comprise the #C$ represent the se'uence of depolarization and repolarization of the atria and ventricles!
ELE>TRO>ARIOGRA< (ses of the #%$ •
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)eart *ate Conduction in the heart Arrythmias irection of the cardiac vector amage to the heart muscle rovides . information aout pumping or mechanical events in the heart
Normal Normal ECG ECG
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The -wave represents the wave of depolarization that spreads from the /A node throughout the atria and is usually 0!01 to 0! seconds "10-00 ms& in duration! The period of time from the onset of the -wave to the eginning of the 3*/ is termed the * interval and normally ranges from 0!2 to 0!20 seconds! This interval represents the time etween the onset of atrial depolarization and the onset of ventricular depolarization! The 3*/ comple4 represents ventricular depolarization! The duration of the 3*/ comple4 is normally 0!05 to 0! seconds indicating that ventricular depolarization normally occurs very rapidly!
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The isoelectric period "/T segment& following the 3*/ is the time at which the entire ventricle is depolarized and roughly corresponds to the plateau phase of the ventricular action potential! The T-wave represents ventricular repolarization and is longer in duration than depolarization "i!e!, conduction of the repolarization wave is slower than the wave of depolarization&! The 3T interval represents the time for oth ventricular depolarization and repolarization to occur, and therefore roughly estimates the duration of an average ventricular action potential! This interval can range from 0!2 to 0!6 seconds depending upon heart rate!
