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