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Posts Tagged ‘sick sinus syndrome’

Tachycardia – Bradycardia syndrome is the hall mark of sinus node dysfunction.

  • The commonest tachycardia in sinus node dysfunction is Atrial fibrillation . Followed very closely by sinus tachycardia . In fact alteration between sinus tachycardia and sinus bradycardia without other pathological arrhythmia is rare . (Of course , we have a name for such an entity as inappropriate sinus tachycardia / bradycardia )
  • Atrial tachycardia occurs a distant 3rd
  • Ventricular tachycardia may be an exception (Please note , extreme bradycardias which lead to pause dependent VT is not directly related to sinus node disease )

The commonest bradycardia in SND is

  • Sinus bradycardia (This fact is undisputed unlike the tachycardia component of SND !)
  • Followed be sinus pause , SA blocks and sinus arrest .
  • AF with slow ventricular response ( Bradycardic AF) We are not sure about the rhythm here (Is it truly junctional /or conducted atrial ? )
  • Associated AV block can occur up to 20 % of patients .If AV block is present the true nature of SA node disease is masked and it’s function becomes almost irrelevant .

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A man  in his 40s presented with an episode of syncope and followed by recurrent episodes of near syncope.

His ECG showed (See image)

  • ECG shows absolutely no evidence of sinus activity . That is  sinus arrest.
  • He lives by the mercy of his AV node.(“Great  escape” junctional rhythm  ! ) . Please note ,  It  fires at less than its intrinsic rate indicating AV nodal sickness as well.
  • The Heart rate is around 18/mt.

SA node is dead(Sinus arrest ) as evidenced by absent p waves. AV node is sick(Depressed) because the junctional rate is less than 20 /mt.

At what  heart rate a person  would develop syncope and near syncope ?

There is no fixed cut off rate for  syncope. It all depends upon the baseline LV function, his exercise capacity, vascular tone etc.

Most will develop some symptoms at  a heart rate less than  40/mt .

Dizziness occur and 30, syncope is sure  when hear rate  dwindles  less than 20 /mt.

A heart rate of 10-15 circulation tends to stall. But still few men are found alive at this rate.

What is the  risk of this patient dying suddenly ?

Contrary to the expectation SCD is not common in  isolated sinus node dysfunction .

It is more common with AV block. The reason being as long as the AV node is fine it will support the rhythm at least at about 30 or s0.

The cause of death in SND is extreme bradycardia induced phase dependent VT /VF.

Will you do a  EP study for him  ?

No. He  does not require it. He is symptomatic ,  and his  ECG shows  tell- tale evidence for SND with AV node depression.

So the there is not even the  necessity to assess  AV nodal status. But .one should  be aware  , there is a battery of tests for SND evaluation (SNRT, cSNRT SACT, etc*) .These are  done only when diagnosis is in doubt or for an academic purpose in teaching hospital.

What pacemaker will you use ?

  • DDDR
  • AAIR
  • VVIR

AAIR can not be used as we have evidence for AV nodal  slowing .

DDDR may be ideal.  In India we still  use VVI mode extensively . Ventricular pacing always safe when you have no EP facilities.  It makes EP study to assess AV nodal function  redundant.

* In all patients with severe bradycardia , a complete workup for systemic diseases like hypothyroidism and other chronic inflammatory pathology must be ruled out. Drug induced bradycardias can exactly mimic pathological  SND. Recognizing these entities could avoid  inappropriate pace maker implantation for  transient reversible bradycardias.

* SNRT – Sinus node recovery time. cSNRT -Corrected sinus node recovery time .SACT-Sino atrial conduction time.

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sinus-node

 

Sinus node  as the pacemaker , orchestrates the rhythm of life . It has  to fire for the entire life time of  a person.It  can not afford to take any rest ! But it can pause a little bit , of course that pause  could  be less  than 15% of it’s basic sinus length. This variation of sinus  cycle length is called sinus arrhythmia.This is physiological. When it exceeds 15 % of the previous sinus cycle it is referred to as sinus pause.

 Have a look at this ECG

sinus-pause-2

 

What follows a long pause ?

By strict terms  of definition a sinus   pause should be followed by  a delayed , next sinus  beat only. A  sinus pause  , many times  is followed  by   JPD – Junctional escape beat.This situation should be ideally  referred to sinus arrest as the sinus node is taking too much of rest and it is not able to wake up from the slumber and it needs assistance form the junctional pace maker.

So even though sinus pause and sinus arrest is used many times interchangeably, it should be avoided. 

What are the electrophysiological mechanisms of sinus pause ?

  • Simple sinus bradycardia . The commonest  mechanism is  the  increased vagal tone. This occurs more often in young athletes. Eventhough increased vagal tone  conveys   a innocuous meaning , at times  this can also be symptomatic  and require intervention.
  • Sinus node exit block.
  • First degree, second degree, complete SA block can occur as in AV node.

First degree SA block can not be diagnosed by surface ECG. Third degree SA block is same as sinus arrest and subsidiary pacemaker will function in these patients.  Second degree SA block is usually diagnosed when the sinus pause is in the multiples of resting sinus cycles. If the pauses are not in exact multiples  sinus arrest is diagnosed. All these arrhythmia’s are collectively called sinus node dysfunction(SND)

How do you manage these patients?

Sinus node disorders can occur in number of systemic diseases*. It  needs to be  ruled out.

  • Infiltrating diseases like amyloidosis, hypothyroid states can result in SND.
  • Drug induced SND like beta blocker and calcium blockers are fairly common and should be excluded
  • Some congenital heart disease (SVC ASD) can involve sinus node.
  • Ischemic SA node disease is rare but can occur  following  infero posterior  myocardial infarction
  • Sinus node disorders are  very often related to degenerative atrial diseases associated with HT, cardiomyopathy etc

*The list is not exhaustive

A very important association is noted  with atrial fibrillation as  a part of tachy brady syndrome .The link between SND and AF  is obvious as   atrial pathology is the common denominator in both ! This will be discussed later.

When is a  pause  significant ?

Any pause that is producing significant symptoms is significant.This depends upon the overall  hemodynamic compensation of the patient.Young, and fit can even tolerate three second pause without symptoms.Underlying heart disease makes even a smaller pause symptomatic.But generally a 3  second or more  pause is almost always pathological .Pauses can be up to  5  seconds (  a 5 second pause actually means a  heart rate of 12/mt , obviously it can not go on for a minute, a patient will develop a syncope). A 3 second pause  corresponds to 20/minute.

How will you evaluate a patient with sinus pause ?

There are sophisticated electrophysiological studies (EP) available like sinus node ECG ,sinus node function studies like sinus node recovery time, activation time etc. But these are generally of  academic interest.

If a patient is symptomatic  (syncope) because of bradycardia  he requires a pacemaker and  EP study is redundant . Similarly , if  he is totally asymptomatic in spite of pauses , again  EP study is  not  indicated.

Only for patients  in the  grey zone,   further studies are indicated .This would include a extended holter, loop recorders, event monitors etc.

Another important issue to consider  is , before putting a pacemaker   patient”s   symptom  must be correlated  with their arrhythmia.

What is  the overlap  between sinus node dysfunction and neuro cardiogenic syncope ?

SND  can occur as an overlapping syndrome with neurocardiogenic syncope.(NCS ).NCS is also a very common cause of syncope .In NCS  there are two limbs .Cardio inhibitory and vasodepressive. The cardio inhibitory form can exactly mimic an SND. In a given patient  it is very difficult to pinpoint which of this limb is dominant.Head up tilt test(HUT)  might help in few.  If a patent’s symptoms are due to inappropriate vasodilatation pace maker may not reduce the symptom of dizziness or syncope.

Management

  • There is no ideal  medical therapy* available as on date
  • Withholding all drugs which might aggravate bradycardia is of paramount importance.
  • Pace maker is the specific treatment in all symptomatic patients.

*Aminophyline tablet may be useful in some patients .It acts by antagonising adnosine receptors in SA node.Other drugs which can incrase the heart rate in the short term include  Orcipranaline(Beta 2 stimulant /Alupent ) Probantheline(M 1 blocker)

The key issue is to avoid unnecessary pacemaker implants in patients who have insignificant pause.

 Which pacemaker is ideal in SND ?

pacemaker

                                                              The need for dual or single chamber pacemker will be taken by the electrophysiologist .Atrial based pacemaker (AAI)  is preferred as it gives physiological pacing .But a simple ventricle based VVI pace maker is good enough in vast majority of patients. This takes care of   future risk of AV block also. DDD pace maker is the most physiological pacemaker and it is supposed to provide better quality of life. But it has an issue of insertion and  maintenance of  two leads, multi parameters to be programmed.It should switch to appropriate modes  at different times.(Like VVI mode during atrial fibrillation etc).Trouble shooting needs expertise , while  VVI is simple,  safe , and just effective as well .(In this turbulent world, quality of life is a  too trivial an issue  to be determined by a DDD  maker)

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