Interpolation and Aberrant Conduction

Report:

Atrial rhythm 75/min

VEBs, interpolated

Rate-dependent incomplete right bundle branch block

Nonspecific T wave changes

Comment:

The actual source of the rhythm is difficult to assign; P inversion in V6 is sometimes held to denote “left atrial rhythm”. Inversion in lead 1 excludes the retrograde pattern of junctional or low atrial rhythms. Whatever their origin, those ectopic P waves proceed helpfully regular throughout the trace.

The VEBs are narrow, less than 0.12”. Their ventricular provenance is shown by slurred V1 descent, interpolation with its concealed retrograde conduction, and different initial vector in several leads.

The basic QRS complexes are rSr’ morphology, a normal variant. The aberrant ones show more delay over the right ventricle, just making it into the 0.10” incomplete RBBB territory.

T wave changes in the first beat of V4-6 resemble, superficially, post-ectopic repolarisation change (the “poor man’s exercise test”) but cannot of course be that – they follow a mildly aberrant rather than ectopic beat and the preceding pause (responsible for the “post-ectopic” change) is absent. What, then? A respiratory swing would show a graded change in the succeeding beats’ T waves. A chance, or artefact? Not so; the trace below shows it, too. Once seen, the answer is simple: the first beat represents the basic pattern and its successors are both RBBB-aberrant, sending their T waves opposite the terminal S wave and making them upright. In some leads (V4 here) aberrant conduction is more obvious by its effect on repolarisation than per se.

Fig 28a. The VEBs unmask the rate dependency of the RBBB, but in the other direction, creating long rather than short cycles (there is no interpolation).

Fig 29. Same 80 year old in ICU: idem, sed aliter.