Variable WPW Conduction
Report:
Sinus rhythm 70/min
Wolff-Parkinson-White type âBâ 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 waveâs 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 â 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 patientâs 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.
Fig 27a. Same patient. The PR segment is more distinct, but still an illusion (vertical line through leads 1, 2 and 3 shows the onset of the QRS complex). Lead 2 is unsatisfactory for ventricular conduction (and so is, by clang association, V2 in this trace).
Fig 27b. WPW âAâ in another patient, with intermittent anomalous conduction favoured by the fast phase of sinus arrhythmia. Again, what looks like a normal PR interval in lead 1 is refuted by the synchronous leads 2 and 3 below.
Fig 28. 80 year old man following ureterostomy and sigmoid colectomy.
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