Cardiac rhythm disorder remains as a fascinating clinical cardiac problem to the physicians for many decades. The joy of decoding cardiac arrhythmias and categorizing into supra ventricular , junctional, ventricular tachycardias is unique , even as many of these patients are struggling for life !
Initially the tachycardias were labeled with reference to their origin .Later as we recognised the locating the origin is not an easy exercise , we introduced a practical classification : Narrow and wide qrs tachycardia emphasizing the fact that , both SVT & VT can be either narrow or wide !
Traditionally there is much more confusion in labeling the narrow qrs tachycardias than the wide qrs tachycardia.
Is the term junctional tachycardia still relevant ?
To answer this question we need to know what exactly we mean by the term Junction.
- Is it a particular anatomical spot called AV node ?
- Is it a diffuse area in the vicinity of AV node ?
- Is the early part of the his bundle included in the junction ?
- Or Is it formed by the entire rim of both AV groove formed by the fibroskeleton that form a electrical barrier between atrium and ventricle ?
Answer:
The answer to the above question is very simple “we don’t know yet !”
The nearest fact is , for the electrophysiologist, AV junction refers to the electrical junction box of that connects the specialised wires coming down from the atria and from there it connects to the specialised his purkinje fibres of the ventricle .
Is AV node anatomically distinct structure?
No .It is not. It is a collection of different conducting cells with varying properties.The term AV node need to be abandoned by the cardiology community for the simple reason there is no such entity.
In fact the AV junctional cells are are now called as pure atrial,atrial approach CELS , junctional approach cells, junctional cells,transitional cells, ventricular approach cells.These cells interdigitate with each other , and has unique cell to cell communication.The cells that are above the AV junction share atrial electrical properties while the cells that touch the his purkinje acquire some of the properties of specialized ventricular conducting properties.
What is the function of AV junction ?
One should realize it is the AV junction does a a very unique job of great importance for human survival ! Even though SA node is the pacemaker of the heart , the AV junction does the extraordinary it receives the impulse and delays it for about 200 millisecond and then hand over it to the ventricle.
The rules that govern the nature is so fascinating , this delay is vital for the venous return to enter the ventricle from atrium other wise , the ventricle is under filled and cardiac output falls.The bulk of the PR interval is contributed by the AVconduction delay (also called as AH interval )
What is the clinical relevance of this new found physiology of AV junction ?
It is to be understood the electrical properties of the AV junction is determined by neural innervation the ionic currents.Much of AV junction is under the dominant control of vagal fibres, while the ventricles get more innervation from sympathetic neurones. There is considerable overlap in the AV junction area.
The classical dual nodal physiology of AVNRT is nothing but longitudinal physiological splitting of AV junction .Strands of slow conducting cells and fast conducting cells are arranged in such a way to create a reentrant circuit.The atrial approaches in the posterior aspect contain mainly slow pathway. and anterior aspect near his contain the fast pathway.
Some times clusters of AV junctional cells are scattered around the upper septal area giving a slow conducting properties to ventricle.These cells can be site for reentrant septal or fascicular VT.
The overlap of these AV junctional cells explains the verapamil sensitivity of some of the VTs arising in the vicinity.
What are the tachycardias that can be termed as junctional tachycardias ?(JT)
By logic and realism any tachycardia that originates in the AV junction either by reentry or ectopic activity shall be called as JT
By tradition , we have been illogical.
AVNRT is never referred to as JT in spite of the fact that, it is initiated by a pathological reentry right in the middle of AV junctional tissue.
So currently we are authorised to call only few arrhythmias as true junctional tachycardia .
- Non paroxysmal junctional tachycardia( NPJT)
- Incessant junctional tachycardia
- Permanent junctional reciprocating tachycardia(PJRT)
- Accelerated junctional rhythm
NPJT
This occurs in following situations
- Digoxin toxicity(Classical description)
- Post operative hearts
- Occasionally during acute MIR
- It may be observed during AV nodal ablation in EP LAB
NPJT is an automatic tachycardia .arising focally from AV junctional tissue . Ideal terminology should be focal junctional tachycardia(FJT) .The rate is between 70 -140. Accelerated junctional rhythm can be termed as a benign form of JT.DC shock has no role.
Incessant junctional tachycardia
This was first described in infants .Thought to be congenital in origin.Now adult forms also recognised.Very malignant arrhythmiaRate is between 150-300. AV dissociation is the norm.May mimic atypical atrial flutter or ectopic atrial tachycardia .High risk for tachycardic cardiomyopathy. Amiodarone may be effective.Surprisingly ,verapamil may worsen it .There is a overlap between adult postoperative NPJT and Incessant JT.DC shock is not effective may worsen . RF ablation rarely effective.
Permanent form of junctional tachycardia
It is not clear what the term permanent denotes ! May be because these tachycardias occur with fixed anatomical substrates.In fact this can be called as a type of AVRT. But the difference is the retrograde ventricular circuit does not travel in any free wall but within the septal his bundle . PJRT, infact may be labeled as AHRT -Atrio hisian recipocrating tacycardia
It is a reciprocating tachycardia with antegrade condction through AV node and retrograde through a slow conducting accessory pathway in posteroseptal location.
The rate is between 90-150. Mimics long RP tachycardia like AT or fast slow AVNRT.Some believe , In fact a fast slow AVNRT can be nothing but a variant of PJRT.
DC shock may be effective only to recur again.RF ablation is very effective .
Final message
Junctional tachycardias are a unique group of narrow qrs tachycardias with differet mechanisms.It is diagnosed in specific clinical settings. They are generally difficult to treat,as the mechanism is often ectopic in nature (Except PJRT).Accelerated junctional rhythm can be termed as a benign form of JT. AVNRT need not be confused with JT , even though it may considered as a junctional reentrant tachycardia.
Reference
Rosen Circulation 1973
Dr.S.Venkatesan MD 