Problems with Lead 2
Report:
Atrial fibrillation with rapid ventricular response 127/min
Intermittent (rate-dependent) right bundle branch block
Nonspecific ST/T changes
Comment:
The L2 rhythm strip demonstrates that this lead is one of the worst (in this case, the worst) to illustrate ventricular conduction. Most of the late QRS is isoelectric there, making the RBBB complexes look narrower than their normally conducted neighbours.
This is not phasic aberrant conduction: the aberrancy arises not from long-short cycle length disparity but from rate acceleration, the critical rate at which the right bundle becomes refractory.
Below (Fig 65a) is a trace with slower ventricular response; the two RBBB complexes are barely distinguishable from others in the rhythm strip. This time there is a long-short sequencing, a true Ashman’s phenomenon. The penultimate beat, a VEB, also has a long-short sequence, but its morphology – a QS in V4-6 and L2 – precludes aberrancy.
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