Posts Tagged ‘medtronic’

In pacemaker science ,  any pacemaker that maintains AV synchrony is often referred to as physiological pacemaker. This is  of course , a  wrong reasoning .None of the pacemakers available today can be claimed to  be completely physiological .All  pacemakers  which paces the right ventricle  induces IVS dysynchrony (Including  the modern DDD)

Single chamber physiological pacing


Paradoxically ,  the most primitive of pacemakers AAI can be the near perfect physiological  pacemaker . The simple explanation  is ,  In AAI mode , expect for the origin of pacemaker impulse the entire depolarisation and repolarisation  is through the normally existing physiological conducting system .(AV node, HIS, Purkinje etc)

(It not only has atrio ventricular synchrony but also  has ventriculo ventricular and intra ventricular synchrony )

So, technically AAIR  is most physiological pacemaker possible .But  the practical utility of such a pacemaker is limited.It can be used  only in  isolated sinus node dysfunction with intact AV conduction . (The problem is the AV nodal conduction can develop later )  To over come this DDDR pacemaker can be programmed to AAIR as a default mode.


This rate adaptive pacemaker  ,  to a  certain extent  can be termed physiological as the heart rate can improve with exercise . (Still it is unphysiological as it  paces the RV )


This is based on the concept ,  for pacing to be physiological , it  requires  atria  to be  at least sensed not necessarily paced.This mode which has a floating sensor attached to the lead as it crosses the atria.This facilitates atrial sensed ventricular pacing .But many believe  the atrial sensing is not consistent in VDD mode.Currently this mode is not popular.There is scope for improving the atrial sensor technology .

Dual chamber physiological pacing


Both  these are the prototype dual chamber physiological pacing modes.

Bi-Ventricular or triple chamber pacing  ( one atria two ventricle)   are our  elusive answers for attaining perfect physiological pacing . it need to be realized, we simply ,  can not mimic the natural cardiac  conduction system.It is  estimated to be more than 10 miles long specialized fibers .

Final message

In our quest for physiological pacemaker we often forget the fact  , AAI is the most physiological pacemaker mode  available .(It even has  VV synchrony !  )

We should use it liberally whenever possible .Of course ,we cannot use it in complete heart block .Still 50 % the  permanent pacemaker  we implant is for sinus node dysfunction. Many of them could be candidates for AAI mode .If current generation cardiac physicians feel out dated to insert a AAI pacemaker, at the least they should program the DDDR into AAI mode with a mode switching to ventricular pacing modes whenever required.

In spite of all  advantages ,  why atrial based pacemakers are not gaining popularity ?

  • Ignorance
  • Lack of expertise
  • Technical difficulty of fixing atrial  lead
  • Perceived fear of lead dis-lodgement.
  • The fact remains  the  ventricular based pacing  is always safe  in case of sudden AV block due to any reason .

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                                          CRT , cardiac resynchronisation therapy  is being  projected  as a revolutionary treatment for cardiac failure , where a failing heart is rewired electrically through multiple leads and make it contract  more effectively.The success rate of CRT was highly variable.The basic question here  is,  there should be a  significant  documentation of desynchronisation  prior to CRT , for resynchronisation to be effective. Further , the sites of  myocardial  stimulation ( Coronary sinus/LV epicardial) , dose of electricity and the sequence of stimulation and the  electrical delay  are very  critical. Achieving this into perfection  is not a simple job and is  real rocket science ! ( If we can achieve 5 % of what  the normal purkinje network do within the LV we can term it a huge success.) Let us hope we catch up with nature . Finally , it is ironical  the sites of LV pacing ,  electrophysiologists  select currently  is infact not selected by them but pre selected by the patients coronary venous anatomy ! .So as on date ,  one can imagine how scientific this treatment could be !

                                         Initially it was adviced for patients with only wide qrs later for even normal qrs patients.When people started using it indiscriminately  insurance companies started to rethink and thus came the   RETHINQ study in NEJM  and brought a full stop to CRT in normal qrs CHF.

How to identify who will benefit from  the costly CRT  ?

It is a million dollar question. So millions of dollars were spent to identify the correct tool to identify the true responders to CRT.Echo cardiography with sophisticated methods tissue doppler, tissue tracking and , 3 D echo ,velocity vector imaging were done .These methods are not only costly but also time consuming and  hugely expertise driven.

Does all this  efforts with  advanced echo techniques worthwhile ?

This simple question was addressed in PROSPECT study in circulation

Click to read the article

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