323: Infarction | How To Read EKGs
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A normal (physiologic) “Q” wave measures less than 0.04 second
Depth measures less than 1/3 height of R wave
An abnormal (pathologic) “Q” wave measures 0.04 (small box) second or greater in duration, and/or the depth measures greater than or equal to 1/3 height of R wave
Once an MI is completed, the ST segment will return to the baseline and the T wave will return to its normal orientation, but “Q” waves are often the one remaining change to a cardiac complex as evidence that tissue necrosis or tissue death (infarction) has occurred.