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Posts Tagged ‘junctional tachycardia’

Junctional tachycardia(JT) is often a misunderstood arrhythmia. Technically,  any tachycardia arising from the AV junction could be termed as JT.Even AVNRT was considered as a form of Junctional tachycardia till recently.The crux of the issue is , true anatomical extent and borders of  so called AV junction is  yet to be clearly demarcated .The common perception that  AV node is a discrete  structure is  an anatomical illusion  , rather its collection of  condensed fibers with proximal  nodal approach and distal fanning .

Now , we have a  proper definition by the apex scientific bodies  ACC/AHA/HRS 2015)

definition of junctional tachycardia

Source :2015 ACC/AHA/HRS guideline for the management of adult patients with supraventricular tachycardia: Executive summary A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines and the Heart Rhythm Society April 2016Volume 13, Issue 4, Pages e92–e135

Please note :The key point is , JT by definition  should  be a focal  /automatic tachycardia either due to triggered activity or after depolarisation and the boundaries of  junctional tissue is liberally extended up to  His bundle.

Read  related post  :What does the term junctional tachycardia mean in current era?

Reference

http://www.heartrhythmjournal.com/article/S1547-5271%2815%2901188-1/pdf

 

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Why Junctional rhythm has huge variation in P wave morphology ?

P waves in junctional rhythm can be

  1. Upright
  2. Iso-electric
  3. Inverted
  4. or  even absent

It depends upon the origin of junctional focus

  1. Site of  entry into RA
  2. Ability to capture inter -nodal pathways  and inter -atrial pathways ,
  3.  VA conduction velocity

Further ,the appearance and timing of P waves will be determined by the underlying structural heart disease also.

Final message

Medical  students  have  grown  up with the belief that  AV junction is a single  focused point .It is  true  in terms  of electrical circuitry  of  normal AV conduction .However  during pathological electrical disorders ( Which arise often because of structural disorder) it should be realised   the AV junction is a huge plane   .   Arrhythmia can occur anywhere from this plane .The entire plane  can become electrically active which may also  acquire the  ability to conduct bi-directionally .

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Ectopic beats , other wise called premature depolarisaton are one of the common ECG abnormalities  diagnosed by physicians.

  • Atrial premature beats (APDs)
  • Ventricular premature beats(VPDs) 

APDs and VPDs  form  the bulk of all clinically important ectopic beats.

Heart has a specialised electrical conducting system , every cell in this system is capable of firing on it’s own. But why then only the atrium and ventricle produce ectopic beats .Other structures like AV node, His bundle , purkinje are relatively rare to produce ectopic beats .

Is the AV junction relatively immune to develop JPDs?

The answer to this question would be  “May be yes” . Yet, we need to recognise they may not be as rare as we think , many times we fail to  diagnose  it or rather recognise it !

Certain observation about Junctional premature depolarisation are made .AV junction has unique properties than any other parts of the heart.The basic purpose of AV junction ( AV node is not a preferred word as it has no anatomically distinct demarcation)  is to apply a electrical break on the incoming electrical signal .Nature does this with a purpose .   It is essential for the ventricles to fill adequately . We call it as PR interval.

So, when the basic purpose of AV junction is slow down the conduction it is logical to expect it won’t get irritated that  easily  and  result in ectopic beats. So JPDs are less common than other forms of ectopic beats.

What is invisible JPD and HIS ectopics ?

We should realise many of the JPDs  & his bundle ectopics are not conducted ,  the impulses simply dissipate down hill .  Unlike the atrium and ventricle the junctional and his tissue has no associated chambers to depolarise , hence they are not  often visible in the surface ECG.The only evidence in the surface ECG may be an unexpected pause which represents concealed conduction. A EP  study  of the bundle  ECG often unmask these silent JPDs and His VPDs.

 JPDs are  less common  , while  junctional escape beats are the  hall mark of any  severe supraventrcualr bradycardia . How  does  that occur ?

AV junctional cells have  an unique behavior in that , it comes to the rescue of the heart whenever the native SA node becomes too slow  . This happens as a passive response .We call this as junctional escape beat.The major difference between a JPD and Junctional escape beat (JEP or JED )  is in the initial timing of the beat . Escape beat comes late .The coupling interval of escape beat (We generally use coupling interval for ectopic beats only , but  it helps to understand )  will be longer than the previous sinus cycle. So escape beat is never premature (Rather a  post mature beat !) .Ectopic beats are always premature ,( except Interpolated ) and occurs earlier than the next anticipated beat.

The other difference is escape beats are tolerated well as the primary purpose is to rescue back up.Their rate is generally equal to the  intrinsic rate  of AV junction ie around 40-50.

General characters  of  Junctional  premature beats and tachycardia

  • Fortunately rare,  fires at a  higher rate.(Unlike junctional escape beats )
  • Enhanced automaticity is a common mechanism
  • Reentrant JPD is rare , unless the patient has AVNRT or it’s variant  physiology.
  • Manifest as narrow qrs complex . JPD with aberrancy is distinctly possible .In that case differentiation from VPD may be difficult.Retograde  P wave morphology may help.But it is non specific as VPDs also have varied atrial capture depending upon the VA conduction .
  • Causes include Hypoxia,  (Rarely ischemic junctional tachycardia. ) common causes include  digoxin induced , post operative states, incessant JT
  • JTs are Difficult to control.Overdrive pacing may be needed. May lead onto tachycardic cardiomyopathy.
  • A benign form of junctional ectopic tachycardia is also reported .

Importance of Junctional escape rhythm

The role of AV junctional escape is vital in extreme bradycardia , as if the junction fails to escape the dangerous ventricular cells take  over  electrical control  and that’s  bad news for the heart  with  sinister consequence.The situation can rapidly degenerate to VT  , what we call  as phase  dependent or brady dependent VT. The treatment for which is increasing the proximal heart rate. By isoprenaline or pacing. So the AV junction does  a delicate balancing act .At times of tachycardia it blocks unnecessary impulses.At times of extreme  bradycardia it assists the heart as escape rhythm . The problem here is many of the disorders that affect SA node , affect the AV node as well .So ,  AV node may not be able to help the SA node always.That is the reason many extreme myocardial end up with VT straightaway.

Final message

JPDs are not very uncommon as one would believe.It has some unique properties. There are vital difference between JPDs and junctional escape beats.JPDs can trnasform into JTs in local pathological milleu and as a rule they are difficult to control.

AVNRT is also a type of  junctional  tachycardia  but,  it  is delinked from  the ( unofficial  ! ) classification of JT  , not  with  any  academic purpose  but by tradition.

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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

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