This is a good strip to demonstrate the change in the appearance of a T wave when a premature P wave occurs on the preceding T wave. The PACs found the atria ready to depolarize and produced a P wave that landed on top of the preceding T wave, making it appear taller than the others. The PACs also reset the sinus node, causing a slight delay before the next sinus discharge. The PACs occurred while the ventricles were still refractory, so no QRS complexes followed.
Jason's Blog: ECG Challenge of the Week, 6-8-12 INTERPRETATION:
1) In first half of strip: Normal sinus rhythm (rate = 100/min) with . . .
2) . . . bifascicular block—right bundle-branch block plus left anterior hemiblock
(RBBB + LAHB), left axis deviation (LAD) at -57 degrees.
3) In second half of strip: Sinus rhythm interrupted by a run of nonconducted atrial bigeminy (arrows (↓); see laddergram).
Jason E. Roediger, CCT, CRAT
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