Pathologic Q Waves
Remember that Q waves can be normal or abnormal. When abnormal, they indicate the presence of an ongoing or an old myocardial infarction. The ECG findings of a pathologic Q wave include a Q wave duration of > 40 milliseconds (one small box) or size > 25% of the QRS complex amplitude. These need to be present in at least 2 contiguous leads to be considered abnormal (lead II and III for example, not leads II and aVF). The exception is the lateral leads V6, I, and aVL where the Q wave duration only needs to be 30 milliseconds to be deemed abnormal. Remember you can localize the area of infarction with an inferior infarct showing Q waves in leads II, III, and aVF and an anterior infarction having Q waves in leads V1-V4 (causing poor R wave progression). Below are some images of examples of pathologic and normal Q waves:
LearnTheHeart.com strives to help medical students, nurses, paramedics, EMTs and other health care workers master cardiology and ECG interpretation. Contact us with any questions or if there is any content that you think should be included in LearnTheHeart.com that you do not see. Submit questions or 12-lead ECG tracings to be included.