Non-Phasic Aberrant Conduction in Interpolated Main-Stem Extrasystoles
Report:
Sinus bradycardia 49/min
First degree AV block
PR interval 0.22â
Interpolated junctional (main-stem) extrasystoles
Non-phasic aberrant conduction
Diffuse T wave changes
Comment:
The interpolated beats are only slightly different from normal sinus beats; their bundle of His (or some such junctional) provenance is shown by their concealed retrograde conduction to the AV node, increasing the subsequent PR interval to 0.30â.
However, they terminate short cycles following twice-as-long long cycles. This is the essence of phasic aberrant conduction, not the non-phasic aberrancy normally seen only in junctional escape beats. Indeed, in lead V1 shortening of the S wave is the earliest sign of RBBB aberrancy13.
This is when I ask the students or the House Staff: Do you believe me or your own eyes? The correct answer to this should be obvious. Below (Fig 24a) is the evidence: a late junctional extrasystole, dissociated from the preceding P wave, has the same morphology as the interpolated ones. That P wave is obviously not conducted, its PR interval being only 0.08â, but the QRS shape proves it further. Here there is no long-short sequencing, but the (slightly) early junctional QRS has the same aberrancy. It is due to its site of origin â slightly different ventricular activation front.
Fig 24a.
Fig 25. Same 70 year old lady as Case 24, showing one possible source of her chest discomfort.
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