Is the Q Wave and T Inversion Normal?
By Ken Grauer, MD, Professor Emeritus in Family Medicine, College of Medicine, University of Florida
Dr. Grauer is the sole proprietor of KG-EKG Press, and publisher of an ECG pocket brain book.
Figure — Limb lead sequence from a middle-aged adult. Is lead III appearance suggestive
Scenario: You are told that the limb lead sequence shown in the Figure was obtained from a middle-aged adult. You note a Q wave and symmetric T wave inversion in lead III.
• Has this patient had an inferior infarction?
• Is T wave appearance in these 6 limb leads suggestive of ischemia?
Interpretation: Clinical ECG interpretation is dependent on history. It is essential to appreciate that ECG findings that might prompt concern in a patient with new-onset chest discomfort may not necessarily be interpreted as abnormal in a non-acute setting in an otherwise healthy individual. Such is the case for the six limb lead sequence shown in the Figure. We note the following:
• A Q wave is seen in lead III. Technically, this is a QS complex, since there is no R wave. Although this Q wave is not particularly deep (it is only 2 mm), given lack of any R wave, this Q wave (QS complex) portends the same clinical implications as would a larger or wider Q wave. That said — Q waves are not seen in the other two inferior leads (leads II, aVF).
• There is fairly deep, symmetric T wave inversion in lead III (especially in view of the small amplitude for the QRS complex in this lead). If this finding was noted in a patient with new-onset chest discomfort, we would clearly be concerned about acute ischemia. That said — there is no more than nonspecific ST-T wave flattening in lead aVF and no ST-T wave abnormality in the other inferior lead (= lead II).
• Clinical Note: The T wave vector often follows fairly close behind the QRS vector. As a result, isolated T wave inversion that often occurs in leads III, aVL or aVF is clearly less likely to be ischemic if the QRS complex is also predominantly negative in the lead that manifests T wave inversion. This is the case for lead III in the Figure.
Impression: We would note the following on our interpretation: "Q wave with T inversion in lead III; nonspecific ST-T wave flattening in aVF; suggest clinical correlation."
• That said, all bets would be off if this patient had new-onset chest discomfort, since absence of abnormality in lead II does not exclude the possibility of acute ischemia/infarction. But if this patient was asymptomatic (especially if a prior tracing was available and showed similar findings) — we would strongly suspect that the ECG appearance in lead III of the Figure was not indicative of ischemia/infarction.
"Take-Home" Point: Most of the time when Q waves/T inversion reflects ischemia or infarction, neighboring leads will show similar changes.
For more information on this review, please visit: http://ecg-interpretation.blogspot.com/2013/11/ecg-interpretation-review-79-normal-q.html.