Far-Reaching Interpolation
Report:
Sinus rhythm.
VEBs, 2 interpolated.
Comment:
The concealed retrograde conduction governing the PR interval after an intercalated VEB rarely affects more than one cycle. In the top and middle strips, the first VEB is intercalated and prolongs the PR interval of two subsequent sinus cycles. This is uncommon119.
Note also the short R-R intervals following the intercalated cycle; this is even more pronounced in the additional examples below. The second beat following the interpolated VEB mimics a premature atrial beat - a sinus extrasystole - except that its P wave is âon timeâ. Its cycle is shortened to the extent the previous one is prolonged through the PR interval.
The PR lengthening following interpolated VEBs is almost invariably obvious, albeit not as marked as in the above examples. In sinus bradycardia, however, it may become invisibly subtle (but, as Tony Seldon, FRACP taught me, âalways thereâ). Below is such a case, from a 79 year old lady in CCU (Fig 144b), with marked LAA and the anterior MI with RAD.
144a. Markedly foreshortened sinus cycles following interpolation.
144b. At 43/min the AV node has recovered enough to conceal the concealed conduction of the VEB. 145. Acute inferior infarction in a 49 year old lady.
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