ECG Review
A Young Adult with Skips’ and AV Block?
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 — ECG from a young adult with "skips."
Scenario: The simultaneously recorded 2-lead rhythm strip in the Figure was obtained from a young adult feeling "skips." What is the rhythm? Is there intermittent AV block?
Interpretation: The challenge in this tracing is to find two normal beats in a row. The only place where this seems to occur is at the very end of the rhythm strip for beats #14 and #15. This tells us that the underlying rhythm is sinus tachycardia. Note how smooth the T wave is in both lead I and lead II for beats #14 and #15.
• Careful inspection of all T waves in both leads of this tracing reveals slight-but-real notching in almost all complexes. This is subtle. That said, other than the T wave for beats #8, #14, and #15, there is a tiny but unmistakable notch or extra peak in all other T waves.
• Each notch represents a premature atrial contraction (PAC).
• Sinus P waves on this tracing are beats #1, #3, #4, #5, #7, #9, #10, #11, #12, #14, and #15.
• The rhythm is atrial bigeminy — in that a PAC occurs in the T wave after each sinus beat.
The Key to interpreting this rhythm is to appreciate the overall pattern. Once you identify two normal beats in a row (i.e., beats #14, #15), you can determine what the "normal T wave" should look like (= smooth without any notching).
• Beat #1 is sinus, but beat #2 occurs early. The notch in the T wave of beat #1 indicates that this is a PAC and not a premature ventricular beat. The reason for the different and wider QRS morphology of beat #2 is that this PAC is conducted with aberration.
• Beat #3 is sinus. Note notching in the T wave of beat #3. This is the result of a blocked PAC (the PAC occurs so early in the refractory period that the entire conduction system is refractory, and the PAC is nonconducted).
• Beat #4 is sinus. Another blocked PAC is hiding in (and notching) the T wave of beat #4.
• Beat #5 is sinus. Beat #6 is an aberrantly conducted PAC. Beat #7 is sinus. Beat #8 is an aberrantly conducted PAC. Beats #9, #10, #11, and 12 are sinus. Blocked PACs notch the T waves of beats #9, #10, #11. The PAC notching the T wave of beat #12 is conducted with aberrancy (= beat #13).
In summary, the rhythm is sinus tachycardia with atrial bigeminy. PACs are either blocked or conducted with aberration. There is no AV block. Given that the patient is a young adult feeling "skips" — one should inquire about potential causative factors (i.e., caffeine or other stimulants) that may be causative.
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