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Posts Tagged ‘m2 receptors’

atropine leafsAtropine ,  the extract from the  Belladona  plant  is an important cardiovascular  drug. It’s  presence is vital  in every crash carts .  This  unassuming molecule  probably has   saved more cardiac lifes than any other drug . It provides immediate  remedy for many of the bradycardias .It  works like a magic.  The physician buys  time with this molecule  and  proceed  on to resuscitate or  plan other interventional  procedures. It is most powerful antiarrhytmic agent known .It is an irony , many of  the standard cardiac texts do not even mention this while discussing anti arrhythmic agents .

In  this  era of  hyped  cardiac  care   , the  sartans ,  2b3a inhitors   , the fondaparinux’s  making merry !  we  have no spare time  to realise  ,   more  cardiac  deaths  have been prevented by atropine  than  all these   drugs    put together.  It is still working like a bull  across the coronary care units and cath lab world over. While  many mediocre  drugs  enjoy a  big  bash  time for  possibly  saving   few occasional  lives   , the atropine  like drugs never get the due recognition among cardiac literature for the simple reason ,  it being a  cheap  generic drug.This drug is available  for few  rupees , no marketing no advertisements, no celebrations.

Mechanism of action

The  biochemical  mediator :  Acetyl choline

Site of action :     It blocks the M2 (Muscaranic receptors) .

We will confine to the cardiovascular  actions.

  • SA nodal acceleration
  • AV nodal accelerated conduction

Effect on ECG

Sinus tachycardia

Short PR interval

Life saving situations in cath labs  in CCU.

Vagus  nerve richly innervate the heart and blood vessels . Acute coronary syndromes   especially involving the infero posterior territory  raises the vagal tone  , and can  in severe bradycardia and hypotension.  In cath labs , as we  manipulate  cardiac  structures with wires and  catheters  there is always  a potential to elicit the vascular reflex .It can occur  any where between the  access point , femoral or radial  artery to coronary arteries .

Further ,  whenever the  pain  intensity is more , the  central pain integrating  centre in  brain stem  and thalamus has a spill over effect into the vagal nucleus .

What happens if a vaso vagal reaction is left untreated ?

We have often  made  the term “vaso vagal  reaction” appear as an  innocuous  entity. The main reason for this perception is   due to the common occurrence of  “vaso vagal  syncopewhich  is largely a benign entity in the general population .This fact  has sensitised our brains . One should distinctly realise the vaso vagal syncope that occurs in  healthy people standing  in erect posture ,  from  vagal reactions that  occurs in  lying patient with a diseased heart  in a  cath  lab  or CCU.In the classical vaso vagal syncope , assuming the recumbent posture is the treatment and it  counters the hemodyanmic imbalance .No drug is required here. So the common vagal syncope can never be compared with potentially dangerous  vagal reflex that occur in CCUs and cath labs. If not recognised earlier and  immediately countered  it can lead on to asystole and death .Many of  the delayed deaths post PCI during sheath removal or an episode of vomiting are directly related to this.

atropine

Atropine is the Savior here . Can you imagine a  world without atropine .

The other reason we had always considered vaso vagal   reactions lightly is that the poor atropine is always available  in the side selfs and it acts   rapidly  and promptly with almost  100 % success  reversing the vagal action  in less than  60 seconds .

How often we here  this  “Oh it’s a brady . . . push  2cc atropine . . .  given sir, the rate has picked up . . .”

If only atropine has a failure rate of say  50%    we  would have  realised the full impact of   vaso vagal shocks (See … how we struggle with No reflow   with no effective drug available !)

Is there any other alternative  treatment  for vaso vagal shock other  than atropine ?

No.   (I guess so . . .Readers may correct me )

Other uses of atropine in cardiac practice

  • During stress testing along with dobutamine  to  increase the heart rate.
  • It can be used to differentiate AV blocks the two types of 2nd degree AV block. The mobitz type 2 worsens while type one accelerates.

Non cardiac uses.

Ophthalmology, pre anesthetic medication, bronchial asthma, various poisoning.

What is the future for this molecule ?

Remain bright .  But only very  few companies make this molecule.  It is a drug that can not  fill the cash boxes but  it is a drug to keep the human heart running at times of crises  . The only  threat to this drug  is  the  possibility of it being replaced with a  modified patented  version of this great  molecule  !

Final message

The evolution of medicine is based on strong foundations  put upon by clinical acumen   by great medical men of  past generation. Atropine was developed by such people   and it has withstood the test of time. This drug  probably  has saved ( and  continue to  save)  many  lives  than any  other drug  in cardiology . It should be recalled ,  another great cardiac drug   called digoxin  has almost succumbed to modern medical  forces  .Let us  keep developing   new molecules  ,  we shall also pay  tributes  to some of   the  unassuming drugs in cardiology .

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