Posts Tagged ‘vvi pacemker’

Every pacemaker has  a metallic “Reed switch” . Putting this switch on and  off is possible with an external magnet .The circuitry is such that , switching on  makes sensing function null and void.It functions as asynchronous mode.In other words  pacemaker converts to a mandatory  pacing mode .All  sensing  related issues are immediately removed.

magnet rate reed switchNote : This switch can be activated by any strong magnetic filed applied externally .And removing the magnet disconnects the circuit.

When a magnet is applied the pacemakers changes the mode in the following way.

  1. VVI  to VOO (Paces only ventricle  without sensing)
  2. AAI  to AOO (Paces only Atria)
  3. DDD to DOO  (Paces both ventricle and atrial with a fixed AV interval )

magnet application permanent pacemaker ecg 002

Purpose of magnet application .

Essentially it may be called as a safety mechanism to prevent external sensing in strong electrical fields in case the need arises.

Indirectly , it may aid us in detecting end of life  of  battery as well

During elctrocautery and related procedures  application of magnet will help.

What is magnet  rate* ?

  • The moment you apply the magnet the pacing rate  changes
  • This is variable with each make and preset.
  • End of life magnet rate will be different . It can be 65 to 85  fixed depend upon the make.
  • Some pace makers  fire initial magnet rates with 3-6 beat fast run and later revert  to steady baseline rate.(One should not be confused )

* Always check with the pacemaker manual for the exact response.

When I put a magnet over nothing happened .What is the inference ?

  • Magnet is not placed properly
  • Pacemaker battery  is totally dead.
  • Very rarely some pacemakers  have magnet function  turned off

What happens  during magnet application in ICD ?

  • There is no change in ICD mode.
  • All anti tachycardia functions are immediately suspended. (A major use in an unusual runaway inappropriate  ICD shock situation )

Is there any risk of applying magnet ?

Since magnet removes the sensing function , interfering a cardiac rhythm which  is dependent on sensing can be  problematic.Similar situation arises in MRI scans and other magnetic fields.

Hence , application of magnet in a patient  as a part of pacemaker trouble shooting who has no pacing spikes is rarely a problem While one should not do it without supervision of  a learned cardiologist.

What is smart magnet ?

Each pacemaker  and ICD  is interrogated with the respective programmer.As such , there is no cross brand  programmer  available.This makes it difficult for patient( as well as physicians)  to call for help in case of malfunction.

The solution is to make standard universal analyser and programmer .This requires  cooperation between various stake holders.Meanwhile as temporary relief a magnet which can community two way with  basic functional switches can be developed .

There is a need for universal smart magnet with constant interaction between device and magnet ..

Since , the generation next generation human  heart  is going to be wired and deviced in a complex manner,  we need to know the basics about these  issues.

Final message

Magnet application is akin to novice’s  pacemaker analyzer. Every cardiac care unit must have one in their shelf. It aids us to diagnose over-sensing as a cause for pacemaker  malfunction.(* please note , it has little  role in all other pacemaker issues !) .In an emergency it can help stop inappropriate ICD shocks.(More importatnly  It gives  time to call an expert ! )


role of magnet application on pacemkakers icd  oversensing magnet rate

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