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Posts Tagged ‘type a and type b wpw’

WPW syndrome remains as  a   fascinating ECG entity ,  ever since it was described by Wolf , Parkinson and White in the year 1930.It is  primarily a  disorder of cardiac embryology . Heart is an organ made up of  tissues from mesoderm and neuro ectoderm.The muscle which comes from mesenchyme has to be incorporated with specialized conducting system. This is a complex  process .It is determined by the bio-genetic forces. When errors happen in the embryonal  tissue  flow  congenital anomalies occur.

In  WPW this  error   happens  exclusively in the conduction  tissue movement  . Normally the specialized conducting system    pierces  the  entire  AV ring and connect atrium  and ventricle  .Later ,   it regresses in  all areas  except in the AV nodal zone  . When  It  fails  to regress ,  these  remnants of  conductive  tissue act as AV accessory tissue  and create electrical  short circuiting .This is the reason , all these pathways are located in the close vicinity of AV ring.

Accessory pathway shows   varying conduction velocity , but generally devoid of  decremental conduction properties .  The presence of such pathways make these individuals prone for variety of cardiac arrhythmias .It can range from  simple AVRT  to  malignant antidromic  AVRTs  that can end up in  VT /VF.

Resecting  these  pathways surgically was once popular.  Effective blocking  of  the pathways with  drugs  is a good option. Currently ,  it is possible to  locate and  ablate  most of these  pathways   successfully.

Even though there are many protocols to locate accessory pathway the one that is very popular is  simple   Type A and type B  WPW , which locates the pathway either in the  left  or  right  ventricle  respectively.

Huge data base  has been accumulated over the past 80 years  regarding WPW syndrome,  still   many questions are unanswered.  One of the important clinical issue is  multiple  accessory pathways , scattered  at  random  across the  tissue planes of atrium and ventricle  .

The other issue is intermittent pre-excitation and shuffling  of path ways during tachycardia  .

It is very rare to see a patient who manifests both Type A and type B pattern during sinus rhythm .Here is an  article from  unexpected  quarters  , Colombo Sri-Lanka in the year 1972  candidly  describes a patient with classical  combination  of  Type A and  B  WPW . It is great to see such an interesting  observation in the pre  EP/Echo era from a remote island nation.

Now , let us ponder over  these questions

    1. Can a pre-excitation  happen simultaneously in both right and left free wall pathway ?
    2. How will the ECG look like  when impulse travels over multiple pathway ?
    3. When dual pre-excitation combines   with  normal AV  conduction  ,     will  it not make  a  triple AV pathway ?
    4. How does a supra-ventricular impulse decide ,  which pathway it is going to travel  when confronted with a choice of  three or  four pathways ?
    5. How do you plan ablation for such a patient  ?

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