Posts Tagged ‘pace maker’

It is one of the greatest innovation in medicine  . . . that is . . . electric current being  used as  a  drug to  treat disorders of heart . Of course ,  it is not a surprising finding  when we know heart is an  electro mechanical organ ,  and electricity can be used  to treat various disorders of heart by delivering it  in an optimal dosage and site.

Devices  that help administer  electric  current in cardiac disease.

  1. External  cardiovertor and defibrillator
  2. Implanted defibrillator
  3. Anti bradycardia  pacemaker
  4. Anti tachycardia pacing
  5. Cardiac  resynchronisation device

What  is  the  difference  between cardioversion and  pacing ?

Cardioversion  is reverting  a tachycardia with  a electric shock that is delivered diffusely throughout the heart This  electrical wavelets traverse the  focus of tachycardia  and the adjoining myocardium  which is called critical electrical mass (Usually reentrant) .This depolarises the cells responsible for tachycardia and extinguishes the abnormal electrical activity.

Defibrillation is same as cardiversion except that it is a high energy shock  and delivered without synchrony with qrs complex . In VF, we defibrillate in all others  we cardiovert .

What are the disadvantages of cardioversion ?

Eventhough it is a very successful modality for treating cardiac arrhythmias it also has some issues.

  • Cardioversion is not infallible. It rarely works in tachycardia due to enhanced automaticity (Multifocal atrial tacycardia , Automatic junctional tacycardia , Digoxin induced tacycardia it may even be dangerous !)
  • Many times multiple shocks are required and may result in myocardial damage, stunning , and elevated cardiac enzymes.
  • In susceptible patients, especially in elderly it may depress the natural pacemaker ie the sinus node and dangerous  bradycardia

over drive pacing paired pacing anti tachycardia

What is difference between cardioversion   applied externally on the chest wall and intracardiac cardiversion as in Implantable cardiovertor defibrillator(ICDS) ?

The underlying principle is same except that the energy required is a fraction of that applied in the chest wall . The average energy required is up to 20 joules . while it requires up to 300 joules

What is anti tachycardia pacing ?   Why this concept came into vogue ?

When it became clear , cardioversion may not work in all forms of tachycardia and risks of multiple shocks  on the myocardium  not be taken lightly , experts in those times (1970s)   thought  a pace maker lead in a optimal site can do the job of cardiovertor. .

Pacing rapidly  in the tachycardia zone  provide us an opportunity  to  enter  the  tachycardia circuit , interfering , interrupting  and blocking the reentrant circuit  (We call it entrainment)  . If it is an automatic tachycardia pacing in close vicinity of the tachycardia   focus result in a  electrical  line of  barrier  which acts as an  exit  block ( Like the lakshman  reka !  in Ramayana )

The term ATP is used as a  general term as anti tachycardia pacing .Over drive pacing  can be used synonymously.

What is the  main advantage of ATP ?

  • Less injury as it avoids recurrent shocks  .
  • Can be administered as many time as  required .
  • Some tachycardias specifically respond to ATP only (Read below)

How to perform overdrive pacing ?

Can we use the external transcutaneous pacemaker paddles for overdrive  pacing ?

Yes we can, it may be termed a  non invasive external overdrive pacing .This  mode is not popular among cardiologists  not because it is ineffective  , rather we have not fully realised it’s  potential .

Different types of  overdrive pacing

What is coupled pacing ?

It is a type of overdrive pacing where   patient’s own spontaneous  rhythm   is used trigger a  pacemaker stimulus    and  hence only alternate beats or pacing beats which is coupled with the pateint,s own rhythm it is called coupled pacing . This  is different from from paired pacing  in that only single pacemaker stimulus per cycle .

What is paired pacing ?

Two pacing stimulus are given.The first impulse is maintained constant and the second impulse is done with varying coupling interval to scan the entire cardiac cycle .It is expected at some point of paired pacing the second impulse would  block the reentrant circuit.

What is random paired pacing ?

The atrium is   delivered a   pair of random stimulus ( . . Like a bite of snake !) is  delivered into the atria .This can revert many of the reentrant atrial and ventricular  re entrant tachycardia.

What is the  unique value of  sinus paired  pacing ?

In patients  with persistent sinus tachycardia,  especially  in patients with  high MVo2 situations or dysfunctional ventricle we have no option to control the heart rate without depressing myocardial contraictility . Most of the negative chronotropic drugs have negative inotropic action also.  In these situations pairing a pacemaker stimulus with a sinus impulse can produce a compenstatry pause  and result  in reduction in net heart rate as well  as increased  contractility due to post extrasystolic potentiation.

How does a  catheter whip inside the atria   terminate many of the procedure related  tachycardias in cath lab ?

It is a common maneuver  in cath lab ,  to  forcibly whip the   catheter for   terminating  many of the transient procedure related  SVTs and outflow tract VTs . The arrhythmias get terminated  either due to catheter hit induced mechano  electrical  cardioversion   (5 joules ?) or  the atrial subendocardial stretch due to the  whip lash .

What are the tachycardias that may  respond to overdrive pacing ?

It is logical to expect any of the reentrant tachycardia  might respond to ATP. The  exact success rate can  not be established  since this modality  is not applied  in vast majority of  patients . Only if a patient  is not responding to drugs or multiple DC shocks ATP is thought off . Of course ATP can not  considered  a first option   unless othe  patient is  on a temporary pacer.

What is the caution for using ATP ? Why  atrial overdrive pacing   is preferred over  ventricular  overdrive pacing ?

Pacing a ventricle rapidly carries a risk of inducing ventricular fibrillation . So whenever  possible ATP  should be administered  through  an  atrial lead. This may not be possible always as in the presence of AV block a VT  can not be captured  by atrial pacing  .

It is also  a fact  many times   when the    ventricular overdrive pacing  fails to revert a VT , an  atrial overdrive pacing has been successful . This is due to the  more uniform    depolarization  wave fronts , that reach the ventricle and reset the VT .

Currently ATP is useful in

  • Recurrent atrial tachycardia
  • Refractory ventricular tachycardia especially with enhanced automaticity (Early ischemic VT )
  • Digoxin induced tachycardias
  • Some cases of Tachy brady syndrome



In some of the modern pacemakers and  in all ICDs ATP is a an important programmable parameter .In fact, using this mode liberally would conserve battery life .Many times a simple hemodynamically stable VTs are shocked by ICDs  instead an ATP will  do the job . It is a well recognised fact that   ATP is underutilsed in ICDs .This issue needs to be addressed.

Final message

Pacemakers are not only meant to treat bradycardias but also tachycardia. Even though it is a well-known fact for over 3 decades, for some reason this simple and effective concept is not getting the  attention of the current generation cardiologists which it definitely deserves!


  1. Overdrive Pacing for Ventricular Tachyarrhythmias: A Reassessment    P. R. KOWEY andT. R. ENGEL
    ANN INTERN MED November 1, 1983 99:651-656
  2. Pacing Techniques in the Treatment of Tachycardias  I. WIENER  ANN INTERN MED August 1, 1980 93:326-329
  3. Treatment of Recurrent Symptomatic Ventricular Tachycardia R. A. WINKLE, E. L. ALDERMAN, J. W. FITZGERALD, and D. C. HARRISON ANN INTERN MED July 1, 1976 85:1-7
  4. Treatment of Tachyarrhythmias by Pacing J. E. Batchelder andD. P. Zipes


Over-drive pacing : A practical approach


Read Full Post »



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



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.


  • 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 ?


                                                              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)

Read Full Post »