Posts Tagged ‘paired pacing’

What will be the pulse rate in a patient who has ventricular bigeminy in ECG with a heart rate of 90 ( 45 sinus beats 45 VPDS/minute ) ?

A.Exactly Same as HR , ie 90/mt

 B.Exactly half of HR , ie  45/mt

C.Can be anything between 45 to 90/mt

D.Any of the above can be true

 The  answer is D . 

I have  noted  ,this simple question in cardiology resident examinations cause great anxiety among students .

Why is it difficult to arrive at an easy answer to this question ?

Traditionally , ventricular ectopic beat were also called extrasystole , implying every ectopic beat shall produce a peripheral pulse .Since ,  we learnt this is not true , we started refering them as VPDs.(Simple ventricular depolarisation which may or may not have a mechanical activity ) So , in a patient whose alternate beat is a VPD  , things become little complicated.

What determines a VPD to acquire  mechanical  energy  or simply  remain as an  electrical event ?

  •  Timing of the VPD* .
  • LV residual volume(LVEDV ) at the onset of  VPD
  • Force of contractility of LV( Of course ,  it is directly related to LVEDV)
  • Temporal relation to  aortic valve opening**

If  the VPD is too early or too late it can not have a mechanical activity . It should be optimally timed midway between two sinus beat to have a good mechnically active VPD. Some refer this as an interpolated VPD .Here, the VPD  becomes a  true extra systole for that individual. So , in patient with ventricualr bigeminy in ECG the pulse rate is usually half , can be same as HR when the coupling interval is optimal or it can be totally irregular as someof the  VPDS gain a mechanical activity and some do not (as often occurs multifocal VPDs. )

* Among the above  four factors timing of the VPDS is the most crucial as it can influence all the other three factors.

** Whatever be the timing or force of contraction aortic valve should be opened to generate a pulse wave. If for some reason this does not happen  there can be intermittent mechanial activity what  we refer to as pulse deficit .

Read a related phenomenon:  Ventricular  paired pacing

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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


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