Traditionally we believed VT can originate only from the ventricular myocardial cells . Then we realised many of the VTs shared the characteristics of SVT. When these were analysed , it was found VTs , after all , do not have a big deal of difference wth SVT s ! especially when it arises from the high septum .Contary to the conventional teaching the AV node is not a anatomically distinct and discrete structure .Instead it is made up of thousands of specialised cells located in AV junctional area .These cells ramify both superiorly and inferiorly like an octopus . Hence , it does not require great academics to understand AV Nodal properties extend downward into the IVS for some distance . In some individuals clusters of cells with slow conducting property (Which is a hall mark of AV nodal tissue ) may invade deep into the IVS .The interface of these slow conducting tissue with that of fast septal purkinje fibres , make it a perfect platform for the potential slow-fast reentry within IVS. This forms the basis of fascicular VT.
Clinical features
- Since it shares the properties of SVT , the natural history is also relatively beningn
- Occurs in young
- Hemodynamically stable ( More physiological conduction : Superi inferior Like SVT)
- Narrow qrs (Narrow because the VTdoes not travel by cell to cell instead run through the normal conduting system for most part in the circuit)
- Verapamil sensitive .(Mimic AV nodal Tach)
- Degeneration into VF is rare and hence SCD is not a big issue
- Tachycardic myopathy can occur.
Note:
Fascicular tachycardia is also known in several names.
It forms the bulk of the causes for idiopathic left ventricular VTs .Other being LVOT VT.
Described first by Cohen in 1974 , followed by Zipes , when they noticed it was possible to reproduce atrial induction of VT.
Belhassen in 1984 found the verapamil sensitivity of this VT
Other synonyms some times used are
- Septal VT
- Narrrow qrs VT
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Fascicular tachycardia
Dr.S.Venkatesan MD 