Abnormal Q Waves: ECGs of Healed Myocardial Infarction (MI)

00:01 So, as the myocardial infarct heals, the EKG develops these initial Q waves and usually they stay there.

00:09 Even years later, the Q waves may tell us, “Oh, there was an earlier myocardial infarct in this zone.” Let's say there were Q waves in 2, 3, and aVF and the patient said, “Oh, yes, I had a heart attack 10 years ago.” Those Q waves are still there because there's a scar there.

00:24 There's an electrically quiet zone in the scar that shows the infarct that occurred in the past.

00:31 So with time, the ST elevation comes down.

00:35 It becomes flat again. Usually the T waves then become inverted and as I mentioned, Q waves can persist as a permanent reminder of the old MI and then over time, the inverted T waves usually become upright again.

00:49 So here, how do we know abnormal Q waves? Well first of all, abnormal Q waves are usually going to be less than one little box.

00:59 So less than 0.04 seconds and less than 2 mm in depth.

01:04 So that means there gonna be less than 1 small box wide and less than 2 small boxes deep.

01:13 And here we see an old EKG.

01:15 This is an old inferior MI. Do you see leads 2, 3, and aVF? There are very significant Q waves there wider than 1 little box and particularly in leads 3 and aVF, they're deeper than 2 little boxes.

01:30 So previous inferior MI.

01:32 Also notice here that the T waves are inverted.

01:35 They haven't come back yet.

01:36 Usually with time they will come back.

01:39 So larger Q waves are pathological Q waves.

01:43 They're usually sign of a prior MI and as I said in this EKG, 2, 3, and aVF show an old inferior MI.

01:51 Another example: here we see, again, Q waves.

01:55 It leads 2, 3, and aVF. This is an old inferior MI.

01:59 Notice the green boxes showing you the Q waves.

02:02 There are abnormally inverted T waves there as well.

02:06 And also notice inverted T waves out in V3, 4, 5, and 6 so this tells you that there's some lateral anterior involvement.

02:15 This may very well be a circumflex infarct.

02:19 Cuz circumflex can give you both supply to the posterior wall and also to the lateral wall.

02:27 Q waves in these leads imply that the MI was not just on the back of the heart but also involved possibly some of the anterior and lateral wall.

02:37 Here's another example: here's a Q wave in leads V1, V2, V3. Notice the green boxes.

02:44 There's a small residual amount of ST elevation in these leads so this infarct may have been within the last few weeks or days and there's also inverted T waves in the rest of the anterior leads.

02:59 Again, telling you this is an anterior wall myocardial infarct.

03:04 The computer frequently will read these findings as anterior infarct age indeterminate.

03:11 We don't know when it exactly occurred. It's not acute. It's not just occurring right now.

03:16 It occurred at some point in the past.