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Is verapamil and beta blockers really contraindicated in AV reentry tachycardias of WPW syndrome ?

Posted Jan 09 2010 1:22am

It is often said , old thoughts  die hard ! It is more so in medical science as we realise ,  perceived fears and  physician phobias  have a long shelf life . A  few  case reports of  verapamil induced acceleration of accessory pathway conduction  was enough , to create a   global  perception among physicians and cardiologists  that any drug which acts on AV node is dangerous in the management of AV nodal reëntry tachycardia (AVRT)

This is a gross perception problem due to dispropotinate importance given to a remote possibility  . Thus ,  a  great therapeutic concept was  put on the back burner.

AVRT is a macro reentrant tachycardia that traverses both AV node  , accessory  pathway  ventricle & atrium .This  tachycardia can be terminated by interuppting  the path way  any where in the circuit .

The most easy and simple option is  to block the   AV node ( Verapamil, beta blockers, even digoxin !)

These drugs have cured many thousands of AVRTs  in the past  .As our knowledge progressed , we  found  , it may not be safe to block the AV node in WPW as it could  divert incoming signals through accessory pathway and result in 1:1 conduction and  possibility of  VF

As soon as this concept was flashed all over the cardiology journals in early 1980s cardiologists  took it as sermon . At the same time, lots of new anti arrhythmic drugs were developed  and this concept came in handy to promote all these new class 1 c and class 3 drugs which are supposed  to act more on the accessory pathway and hence projected to eliminate the risk of  VF.  

It was never  minded ,  all these new group of drugs has it’s own pro arrhythmic  properties  like  prolonging   QT interval   and has a potential to precipitate dangerous ventricular arrhythmias 

So, by the turn of   millenium calcium blockers and beta blockers have been removed form the  cardiologist mind in the management of WPW/AVRT

What is the reality ?

Verapamil or betablocker induced sudden death in WPW is a grossly exaggerated concept in clinical cardiology .Treatments and procedures with many fold risks is being practiced in every walk of cardiac patients.

Complete heart block  and related morbidity  during RF ablation of WPW syndromes can easily exceed the   of verapamil induced  side effects  in WPW.

 How to  identify potential patients who are likely  to develop complications  with AV nodal blockers in WPW syndrome ?

The key determinant is the accessory pathway refractory pathway . If it is < 250ms  the chances of accelerated conduction is considered high. EP study is needed to measure accessory path refractory period.If it is > 300ms the accessory pathway is unlikely to condcut fast .

Is there a  non invasive bedside method  to estimate  accessory pathway refractory period?

NO, It is not possible , but some clinical clues are available .

  • All concealed accessory pathway have very high RP *thats why they are concealed .Since they can not conduct antegradely   resting  baseline ECG do not show any evidence for preexcitation . They  are  safe .
  • These patients can develop only orthodromic tachycardias as the accessory pathways allow only a retrograde conduction  and AV nodal blockers are ideal in them as there is no purpose to use Amiodarone and  related drugs as antegrade  condction thorough accessory pathway is naturally blocked .
  • Intermittent WPW syndromes  have negligible risk of fast antitrade conduction. As episodes of  disappearance of delta wave indicate the antitrade conduction has a tendency to get blocked so no great worries.This is especially important if the WPW disappears at higher heart rates .

This clearly tells us  , many times  accessory pathway  shares some of the decremental properties of AV node (Applying automatic  electrical  breaks at higher  heart rates ) and it is a safety mechanism .The exact incidence of such property is not known . So , it may be a good idea  to subject patients with WPW on a treadmill and look for it’s  influence on delta waves and degree of pre excitation  .Even a few normalised beats  or prolonged PR intervals can give us assurance  against  rapid rates at times of  AF .

*One should  also remember , if a concealed WPW , manifest only during excercise it is the most dangerous group of patients in whom AV nodal blockers are absolutely contraindicated . They are immediate candidates for ablation . The above phenomenon  tells  us  , during excercise  the  AV node expresses the decremental conduction properties while accessory pathway  does not !

 Final message

Verapamil and betablockers are not  the  drugs to fear upon in WPW syndrome.In fact ,  even in this era of  hi tech cardiac care , it has a  useful role to  play  in the chronic management of WPW .

May be ,  it need to be  used with  caution . Atleast  , some  efforts  must be taken to estimate the refractory period of accessory  pathway before prescribing these drugs.

Using with caution is not synonymous with contraindication   

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