What does a significant Q wave indicate?

Technically, a Q wave indicates that the net direction of early ventricular depolarization (QRS) electrical forces projects toward the negative pole of the lead axis in question. Although prominent Q waves are a characteristic finding in myocardial infarction, they can also be seen in a number of noninfarct settings.

Which ECG leads have Q waves?

Small Q waves are present in the left precordial leads in more than 75 percent of normal subjects. They are seen most frequently in lead V6, less frequently in leads V5 and V4, and rarely in V3.

When do Q waves appear after MI?

Q waves may develop within one to two hours of the onset of symptoms of acute myocardial infarction, though often they take 12 hours and occasionally up to 24 hours to appear. The presence of pathological Q waves, however, does not necessarily indicate a completed infarct.

What causes Q waves on ECG?

Pathologic Q waves are a sign of previous myocardial infarction. They are the result of absence of electrical activity. A myocardial infarction can be thought of as an elecrical ‘hole’ as scar tissue is electrically dead and therefore results in pathologic Q waves.

What are the ECG criteria for Q waves?

ECG criteria for pathological Q-waves (Q-wave infarction) Lead Definition of pathological Q-wave Normal variants V2–V3 ≥0,02 s or QS complex* None All other leads ≥0,03 s and ≥1 mm deep (or QS complex) Individuals with electrical axis 60–90°

How are Q waves used to diagnose STEMI?

Establishing a diagnosis of Q-wave infarction requires that pathological Q-waves be present in at least two anatomically contiguous leads. In patients with STEMI, ST-segment elevations and pathological Q-waves occur in the same leads, which is why pathological Q-waves can be used to localize the infarct area.

When do Q waves develop in myocardial infarction?

Myocardial infarction – particularly if extensive in size – typically manifests with pathological Q-waves. These Q-waves are wider and deeper than normally occurring Q-waves, and they are referred to as pathological Q-waves. They typically emerge between 6 and 16 hours after symptom onset, but may occasionally develop earlier.

Are there Q waves in the left heart?

They are usually absent from most leads of the ECG, but small Q waves are normal in the leads that observe the heart from the left;