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Posts Tagged ‘wpw syndrome’

Localising  WPW syndrome is a favorite  time pass  for cardiologists in spite of  serious  limitations of surface ECG .Still , it is vital to generate a rough idea about the location of  these pathways ,  so that we can focus  our efforts  on  some sort of ablation procedure .

Arruda algorithm is probably a simple and fairly useful technique to remember. It asks us to climb 4 steps   and pause at each  step and look sideways   for the accessory  pathways !

Step 1 (Left free wall step )

Initially one need to look only two leads .

Look at lead 1  and  V1 for   delta wave and R/S ratio .After Identifying delta wave look for the polarity of delta wave (This can sometimes be really difficult ) .If there is iso-electric or negative delta it immediately  fixes the pathway  in left free wall . Similarly if V1 R >  S it also fixes in left free wall. To locate more precisely in left free wall  look  for  delta  wave polarity in  AVF  and proceed down*

If none of these finding are present then  Go to step 2 .

Step 2 (Coronary sinus step )

It is the most simple step . If negative delta  located in lead 2 (often mimic inferior MI)

Here the pathway is often located in coronary sinus /middle cardiac vein often as diverticulum.

After excluding left free wall and coronary sinus origin one has to look at possible septal  pathway  .

For this  go to step 3

Step 3  (Septal step ) And  again v1 lead  becomes important if v1 shows negative or iso-electric  go down  to septal  pathway decoding

After ruling out septal origin the scheme takes us to right free wall by default.

Step 4  (Right free wall step)  If the delta wave does not fit in  any   of the above three steps (Including  positive  delta in V 1 )  it  fixes  the right free wall  pathway

Arruda scheme summary

Arruda scheme  guides  us  to scan  systematically  for pathway from left free wall  to  septum and lastly  the right free  wall  (The key  to  locate  the APs is  to look at  delta waves in lead  1, 2  AVF and R/S ratio In V1 )

Here is a  simplified version for basic localization

Reference

  1. Arruda MS, McClelland JH and Wang X , et al. Development and validation of an ECG algorithm for identifying accessory pathway ablation site in Wolff-Parkinson-White syndrome. J Cardiovasc Electrophysiol 1998;9:2–12.

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Most  cardiologists  are familiar with  “Circulation” . We know  it  is a top  cardiology  journal with highest impact factor.  Few of us are  aware  of  a journal called  “Circulation  research” ( I wonder  why it is named  like that ,  as if  the regular   circulation journal  does  not carry research stuff  !)

It is one of the  path breaking   journals that regularly  churn out state  of  the art , often  mind  boggling research stuff.  Once in while we should get a feel of  basic science  research  as it  happens.

How else we are going to know an  atrial cell is to be bio engineered  shortly to behave like a  SA node  in patients with sinus node dysfunction. (Biological pacing )

This team from academic  medical  centre Amsterdam   should be credited   for  publishing   this gem of  an  article   from  a  study  involving the  measly mice !

It  deals elaborately  about the embryonic basis of AV nodal  disorders  . Specifically it  explains  the genesis of  WPW syndrome and how AV rings get muscularised  .

(It  is  due to   error in  bio-genetic forces ,which  affect the    incorporation  of AV nodal tissue  in the  fibrous  skeleton .This   results  in ectopic  junctional  tissues appear   any where along  the AV ring . This is the basis of  accessory AV pathway and   clinical  re-excitation.)

Final message

Once in a while  we should develop the habit of reading  tough  journals  like circulation research . After all ,   if a cardiologist  is not reading   these stuff who else  . . . will  ?

Reference

http://circres.ahajournals.org/content/107/6/728.full.pdf+html

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WPW syndrome is the prototype of cardiac pre- excitation . The accessory  AV pathway short circuits the ventricle .Since  there are two options  available   for the  incoming  atrial  impulse  to reach ventricle ,  often  times  the qrs is contributed by both .Hence a  fusion  occurs  within qrs complex and stretches it wide   ,  it also  generates a delta wave and short PR interval .

The complexities of  conduction   properties and refractionaries of AV node and  accessory  pathways determine the degree of pre- excitation. When an optimally timed  APD  gate crashes  into the  accessary pathway it gets blocked ,  only to recover little late ,  unfortunately  invites AV nodal impulse  from below  . This facilitates a  re- entry circuit from ventricle to atria and result in classical AV reciprocating tachycardia .

Antegrade conduction through AV node is  physiological and  benign as it inherently checks the heart  rate . Antegrade conduction  occurring through the  accessory pathway  (which  constitutes the pathological  component  ), is   potentially  dangerous  as it lacks the  electrical breaks (Technically called decremental conduction )

What  is the  specific  ECG evidence for  antegrade conduction thorough accessory pathway  in ECG ?

Delta  waves

So,  what does it mean if there is absent delta waves  in WPW syndrome ?

It can mean three things

  1. Concealed pathway
  2. Manifest pathway , but intermittently  blocked pathway.
  3. It is not WPW syndrome at all .

We know concealed  pathways are  safe* as it allows only retrograde conduction. ( Safe  regarding   risk  of  sudden cardiac death ,  still unsafe for AVRT !)

Intermittent WPW

Intermittent pathways are equally  safe  as intermittent absence of  pre-excitation   indicate  the  presence   of naturally occurring     breaking system within accessory pathway . Are these  accessory pathways blessed with some AV nodal cells ?  May be !  . Histological studies do suggest that .This explains   intermittent missing of delta waves  which is  electro-physiologically a good sign

(We also know   there are exclusive slowly conducting accessory pathways like  Mahim and variants  )

If  one is lucky to observe this phenomenon in ECG  it can be termed as  a poor man’s  EP study  . ( Which requires specialized methods to document the refractory period of accessory pathway  to be   < 250 msec)

Techniques to  screen for or / unmask this concept.

Whenever  we  diagnose  WPW one has to look   ,  whether the patient  harbors  this phenomenon .

  • Holter monitoring has a useful role in this regard .
  • If there is nocturnal   disappearance of pre- excitation it would  suggest a safe  accessory pathway.
  • Similarly , if pre- excitation disappear during exercise  stress  testing it  would indicate a  type of intermittent WPW syndrome.

Final message

An astute cardiologist shall  look for this intermittent nature of delta waves  and  help avoid a costly and  potentially harmful EP study !

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 Delta waves  are initial 20 ms  (or is it up to 40ms ?)  segment of  qrs complex that is  inscribed due to pre-excited depolarisation of the ventricle due to an accessory pathway .

It is more of a  fusion complex with  native normal qrs complex. The leads in which appear , the polarity and magnitude of these delta waves are determined by

  • Site of APs
  • Rapidity of  conduction through this AP
  • The quantum of native AV conduction
  • Influence of Autonomic tone  and the  refractory period of these accessory pathways .
  • Heart rate , distal conduction velocity , also can influence .

Can delta occur without AP ?
Like any other variation  isolated delta waves are reported in routine ECG finding.   It can be  be present in 0.15% to 0.25% of the general population. A higher  prevalence of 0.55% has been reported in first-degree relatives of   patients with accessory pathways.

How do you account for delta in general population ? We know concealed pathways can not record delta  . . . then it is possible some from of accelerated AV conduction  with twin pathway should be quiet common . ( It is very much possible  dual AV nodal pathway with grossly different conduction properties and distal insertion sites  inscribe a delta wave .)

  The crux of the discussion  of WPW syndrome revolves around  identifying delta wave and its direction .  If  the delta wave is well inscribed this job is easy  but at times  it  can be really difficult .

Many moods of delta wave

  • Positive delta  wave inscribes  above baseline. (See the above ECG  showing different delta in same patient )
  • Negative below baseline  and  iso-lectric on the baseline .
  • Please note , delta wave polarity and QRS polarity need not be in the same direction . If  they are in  the opposite  direction many time it appears as  small a pathological “q”  or pathological  “r”
  • It is likely  a delta wave can also drag  and  change the direction of qrs depolarisation  if  the  quantum pre-excitation  is large and with a fast conduction property.
  • It is also possible  the combined contribution of  negative delta with negative qrs together make a  deep  q waves . (Typical example is the LBBB type ECG in type B WPW in Ebstein anomaly )
  • Rarely the entire QRS can be  due to pre-excited  tract and native AV conduction contribute less.(This exactly happen in anti-dromic tachycardia ) but  this phenomenon is extremely rare to occur without tachycardia.

Final message

WPW  syndrome is such a dynamic  entity ,  one can realize how futile it will be to formulate fixed rules for ECG localization based on this wave .In fact,  we suffer from a  fundamental  electrical ignorance .How often delta wave polarity is discordant with qrs polarity and what is the  mechanism ? Standard text books do not discuss this issue . Many of the EPs skirt this question ! For this , we need  to critically decode the mechanisms of delta wave generation . Hope our youngsters take up the job !

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Pectinate muscles are specialized Intracardiac  muscle

  • Pectinate muscles are located mainly in the right atrium  , more  in right atrial  appendage , sparse in left atrium
  • Has muscle fibers arranged in a  comb like fashion.
  • Has less mechanical activity, no significant contribution to atrial contractility.
  • Can stretch and improve the voluminous nature of right atrium
  • The pectinate muscle  folds act as RA volume reserve  during adverse loading conditions . It helps RA dilate with out much wall stress.
  • Rarely it can be a cell of origin for focal atrial tachycardia

Image Source : Greys anatomy

The concertina like effect of pectinate muscle .

The atrial infolding increases the surface area of atrial chamber at times of dilatation , like  the music instrument .So,  these macro  folds ( like intestinal villi )  help overcome the  constantly changing volume status of right atrium.Since the  variation  left atrial blood flow is  not that much ,  the pectinate muscles  are not well developed  in the left atrium.

The same rules would apply for  why  there is excess  trabeculations  in right  ventricle  than  left  ventricle .

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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

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

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Echocardiography is an imaging tool . Can it  be used as a non invasive  EP lab ?

Heart is an  electromechanical organ . For every mechanical activity there must be a electrical event preceding it . So, when we analyse the cardiac contraction and relaxation it indirectly provide us clues how the electrical activity spreads across the heart.

The concept of using echocardiography for diagnosing cardiac arrhythmias have never been popular for the simple reason we have a cheap and best modality : The ECG.  But, it  does not give us the temporal relationship with the cardiac contraction. When these two are combined it can be a really powerful tool to analyse many cardiac arrhythmia.

  • In fact ,  for every brady and tachyarrhythmia there has to be an unique pattern of IVS motion and mitral , tricuspid valve movement.
  • Almost all bradycadias can be diagnosed with echocardiogram by virtue of analysing the timing of  atrial vs  ventricular  contraction.
  • We know echocardiogaphy is the only modality available to diagnose fetal cadiac arrhythmias.* (How can  this modality becomes useless when the baby comes out of the mother’s womb  !)
  • Apart from this there is an  unique use for echocardiography to locate accessory pathway in WPW syndrome

The premature contraction of LV can be seen in few as  an early systolic dip in IVS movement -Type B WPW.

Image courtesy :  Helmut F. Kuecherer Circulation 1992;85:130-142

Abnormal jerky movement of LVPW indicate left accessory pathway -Type A WPW

Newer modes of echo like tissue doppler will improve the phase analysis of tissue motion and may provide us accurate information about preexcitation

Final message

The future looks bright . Time is not  far off . . .  where ,  we shall  use ultrasound as an adjunct  EP  study .

Reference

*Fetal Echo  =  to  Fetal electro cardiogram

WPW syndrome

http://circ.ahajournals.org/cgi/reprint/85/1/130.pdf

http://content.onlinejacc.org/cgi/content/full/33/3/782

http://www.heartjnl.com/cgi/content/full/82/6/731

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