Variable WPW Conduction
Report:
Sinus rhythm 70/min
Wolff-Parkinson-White type “B” conduction
Concertina effect
Comment:
Most of the time the PR interval is so short that the end of the P wave overlaps the delta wave and the P wave may be mistaken for an ectopic deflection or even missed. Here, from the second to the sixth complex, the delta wave’s contribution waxes and wanes back, revealing the full extent of the P wave. The PR interval, albeit short throughout, increases and recedes accordingly. This is not very obvious in this example, but can be discerned by a willing eye: the concertina effect. Variable degrees of fusion between normal conduction and a ventricular ectopic or paced rhythm produce the same effect. WPW conduction is also a fusion phenomenon – the divided impulse fuses with itself.
More often, WPW conduction causes changes in axis and QRS appearance in tracings taken at larger time intervals. Below is one of the patient’s ECGs taken a month earlier: its axis is normal and the P waves stand out clearly in lead 2. The inferior Q waves are present, but smaller.
The LAD and the inferior QS complexes are discounted in reporting when (and sometimes, if) WPW conduction is recognised.
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