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Posts Tagged ‘apd’

Sinus node is the electrical high command of our heart .When it gets injured  seriously (or shot down   as in sinus arrest ) there is utter chaos in the lower ranks !

This is what happened  in this patient .

trigeminy group beating vpds sinus node dysfunction escape capture

The lower pacemkers can either passively release  themselves as escape rhythm or actively fire with a  ectopic focus  . Any combination of escape / ectopic  beats can  occur .If occasional sinus beats capture the ventricles things  can become further complicated .

It is obvious , this  random intra-cardiac  shooting  makes the life of the  myocardium miserable . It is a perfect setting for syncope, tachcyardic cardio myopathy , extreme brady induced VT , VF  even SCD.

*Meanwhile , It is  heartening to note  SND   rarely lead to  sudden death in spite of all the chaos .However  extreme  bradycardias  that occur in  complete heart block  does  not enjoy this immunity as fatal complications are common if not intervened .

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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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Logic would suggest  any two structures  in close proximity can have  some sort of anatomical , physiological or sometimes pathological relationship .Esophagus and heart  share a strategic  anatomical  space within the mediastinum  . The left atrial wall  is abetting the esophagus with only few millimeters separating the two. Trans esophageal  echocardiography has utilised this proximity for it’s  advantage . With the probe in esophagus we can get a  100%  interior view of left atrium . Both these structures can mutually compress one another at times of pathology . ( LA compression on esophagus in mitral stenosis , Esophageal compression of LA in hiatus hernia or esophageal growths) . Now ,  we also  realise , esophagus  a   functionally unrelated structure  to  cardiovascular system  can have a impact on cardiac functioning.

Hiatus hernia of gastroesophageal junction can mechanically compress the posterior aspect of heart and result in atrial  arrhythmias and pericarditis  ?

Reference

1 Duygu H, Ozerkan F, Saygi S, et al. Persistent atrial fibrillation associated with
gastroesophageal refl ux accompanied by hiatal hernia. Anadolu Kardiyol Derg
2008; 8(2):164-165.

A case report from South africa

http://www.saheart.org/journal/index.php?journal=SAHJ&page=article&op=view&path[]=115&path[]=109

Read further for esophagus- heart  stories.

  • Esophageal ulcers , spasm can trigger electrical activity that can mimic cardiac event  or rarely precipitate a real angina  , what is often referred to as  linked angina .
  • A rare case of pneumopericardium due to rupture of esophagus into pericardial space
  • ST elevation in ECG due to esophageal spasm

http://www.drsvenkatesan.com

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Ectopic beats or premature depolarisations are the commonest  cardiac arrhythmia encountered . Human heart , is a  non stop  electro mechanical organ ,  and it is not surprising   ectopic beats are so common  and can literally originate  from every cell of heart. But , generally it   emanates  primarily from  the special conducting cells . At times  ,  even  other cells (Myocytes, interstitial cells )  can generate abnormal electrical potential.These ectopic electrical potentials  can be compared  to  electrical load shedding when there is excess electrical strain .

Vast  majority of ectopic are benign  in human population. When this occurs ,  in the milieu of underlying heart disease or during ischemic  episodes they become clinically important and initiate a sustained arrhythmia.

Classically and traditionally ectopic beats are described in the

A.Ventricle :      Ventricular premature beats, (VPD)

B.Atrium:             Atrial premature beats(APD)

C.AV junction : Junctional premature beats.(JPD)

If you note , one important structure is missing from the list.

Yes , it is  SA node.  Can it result in premature depolarisation ?

When do you suspect a SPD(Sinus premature depolarisation)

  • It manifests a  an sudden unexpected , sinus beat exactly as the previous sinus beat. Followed by a pause.
  • The P wave morphology exactly is similar to prior p wave.
  • Many times we miss this entity as we tend to over  diagnose APD than SPD.
  • SPDs tend to occur in bigeminy rhythm.

Differential diagnosis

  • Sinus arrhythmia and pause
  • APD
  • SA node echo beats (Part of SA node reentry)
  • SA blocks

How do differentiate  a sinus arrhythmia from sinus premature depolarisation (SPD ) ?

Sinus arrhythmia occurs in a baseline bradycardia environment.

It does not not come as   “on -off ” pattern . It has a gradual onset offset dynamics.

Clinical significance

This is a clinically unimportant arrhythmia* .This  is probably the reason , it is not a popular concept .

*But it can confound in the diagnosis of  , other important rhythm  disorders.it could be a expression of  sinus node dysfunction and a precursor of  inappropriate  sinus tachycardia The significance could be substantial in atrial triggered  based  pace maker rhythm

Final message

When you confront an unexpected , early , sinus beat not accountable to sinus  arrhythmia  or APD

suspect SPD.It is  not rare , it is a  grossly under diagnosed entity.

Reference

Sinus premature systole  http://www.chestjournal.org/content/64/1/111.full.pdf?ck=nck

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