Posts Tagged ‘chb’

For the lay public   the term complete heart block (CHB) often convey a sinister message . When  encountered in   pregnancy,  it is   frightening    for the  physicians as well .  One need not  say  . . .the anxiety to the Obstetrician !

Congenital complete heart block is the usual etiology. Though there are other important causes of CHB in general population , it is very rare to  get an  ischemic or  degenerative heart  blocks  in the reproductive age group.

There are  many  ways it can present .

How does it present ?

  • Symptomatic CHB detected  first time during ante natal screening
  • Asymptomatic CHB detected incidentally during ante natal screen
  • CHB first time recognised during active  labor. Either symptomatic /Asymptomatic
  • A more familiar  situation  is  CHB  diagnosed in child hood . Women in question can undergo an  elective marriage and a managed  pregnancy.

* The success of modern medicine  lies in the  mantra  of  “early  diagnosis ” .Ironically , early detection  of CHB in  pregnancy adds  considerable anxiety  to mother , family  and the treating physician  . So ignorance  can be a  bliss here ,  as 99/100 with CHB  would not require any intervention during pregnancy  .But , in this hyped up scientific world  one  needs  lot  of courage to  simply watch a pregnant mother with a heart rate of 45  !   .You are tempted to do something . We have seen CHB presenting  in labor room as emergency and delivering successfully  by vaginalis .

Where is the pathology in congenital complete heart block ?

It is  usually due to anatomical discontinuity between AV node and the bundle of his. The most fortunate thing  here is ,  these patients  develop a junctional escape rhythm at around 40-45/mt .This is enough for most basal activities. Further this junctional rhythm can increase   up to 100 in many, or  even up to 120 at times of stress.(Accelerated junctional  rhythm )* .An ECG which shows a narrow qrs  complex is nearly  100 %  specific  for a stable junctional escape rhythm.

What is the hemodynamic stress of pregnancy ? Will a heart rate of 50 /mt enough , to support the labor or cesarean section ?

Nature  is a wonderful equalizer. What the pregnant mother requires is a good cardiac output to nourish the baby as well as herself. A heart rate of 50 is often able to sustain and support the entire pregnancy with ease.

How it is done  ?  . . . is  it not simply  amazing ?

In pregnancy there is less of  systemic vascular resistance due to various reasons (Low impedance  placental circulation, reduced sensitivity to Angiotensin 2  ) . The heart can always increase it’s out put by increasing  the heart rate or stroke volume.  In  patients with CHB , as the  rate can not be increased much , the heart  accepts  the  alternate option quite easily without  any protest  . The low SVR also facilitates  increase in stroke volume. This  is the reason pregnancy  is  often well tolerted  even with the heart rate < 50 /mt.

But , at the time of delivery increase in heart rate may be important in some.We do not know , who will require this HR support .This makes it mandatory to have a  temporary pacer standby.

What are the ominous signs and symptoms of CHB in pregnancy ?

Having discussed a lot about the benign nature of congenital CHB ,  one need to realise it is also a potentially dangerous heart rhythm . Syncope, symptomatic hypotension  (BP<90) and some times  signs of PIH ,  all possibly indicate a pacemaker support .

Can we do an exercise test  to  assess  the chronotropic competence in pregnancy ?

Tread mill test is generally not done  in pregnancy. It is a good option ,  to test the adequacy of heart rate increase during activity . If the heart rate increases up to 100 -120 it is a good response .

What about holter ?

A less predictive , but more acceptable investigation is the 24 hour holter monitoring  that gives a rough idea about lowest and highest heart rate. If there is a  long pause > 5 sec ,  she will be a technical candidate for permanent pacing !  once you have documented this ,  we will be sued if not paced however asymptomatic the patient is ! So beware of this investigation !

Atropine stress test ?

This again is a simple test , that will measure the chronotropic reserve. A concern for fetal tachycardia is genuine !

Pre-conceptional  counseling

A patient with congenital complete heart block should never be adviced against pregnancy.

“Pace and become pregnant ” strategy is also not warranted.This is based more on the perceived  scientific approach the and  litigation  fear  than reality !

Only issue is we have to make sure ,  the women in question has  adequate hemodynamic reserve. This  can be easily accomplished  by asking some basic questions about exercise capacity .Or , she can be put on a  tread mill (or atropine stress test). If the heart rate increases up to 100/mt  there is absolutely , no need to put  permanent pacemaker.

Peculiar  issues in   pregnant  women with permanent pacemaker

The paradox of modern medicine  felt at it’s  best here !

We think ,  we are  implanting   a  pacemaker in CHB of  to provide good hemodynamic support  during the stress of labor. But a  fixed rate VVI pacemaker will not do this job . The real reason  to put a pacemaker is to avoid a dangerous bradycardia during the labor .

Hence ,   patients  with CHB carry equal  concern (if not more !)   during labor as the pacemaker fires at a  fixed  rate of 70/mt and  the native rhythm is often suppressed due to long-term pacing . Hence their heart rate often fail to increase   beyond the pacemaker rate of  70  . Paradoxically , patients with untreated  CHB (with their native rate ) , can increase their  heart  rate often up to 100-120  at times  of stress .This is possible because  their AV node is still under the control of autonomic system , while artificial  pacemakers* are not !

*Some of the current pacemakers have overcome this problem with rate adaptive pacing .

Mode of delivery ?

  • Natural , expected
  • Induction  of labor
  • Elective cesarean
  • Emergency Cesarean

Can complete heart block per se , become an  indication for cesarean section ?

No. It is always an obstetrical indication .It  is better to avoid GA / Regional anesthesia  in cardiac disease. The stress of  second stage of labor is always less than   that of   surgery provided it is not unduly prolonged .

Assisted /accelerated vaginal delivery is the  best option .However , one should be ready for any intervention. Some obstetricians  feel  that, elective cesarean section  could  be less stressful than  labor( which could be prolonged for some unpredictable reasons  ) while a ,  Cesarean section  can not  be a  prolonged one  !

Cardiologist’s role in the labor room

The role of cardiologist is to provide support to the obstetrical and anesthetic team   prevent   extreme bradycardia. Inserting a temporary pacemaker with back up pacing of 50/mt is preferred.Trans-jugular approach is ideal .In difficult cases fluroscopy guided temporary pacing in cath lab is advised.

Role of temporary trans cutaneous pacing  as stand by ?

This method of pacing with two sticky electrodes in the chest wall  with external pacing .It is proven , efficient useful modality of pacing in coronary care units  .However this can be a substitute for  only few hours of support . May have patient discomfort .In places from expertise for temporary  pacing is not immediately available  this can be used .However presence of such a machine increase the comfort level of physicians.

Is there a rate adaptive temporary pacing available ?

Currently available temporary pacemakers  are not rate adaptive , and hence we have to pace  roughly at  about 90 or 100 give  allowance  for labor related demand  (We would not know, how much  the mother is compensating with increasing with  stroke volume ) in this case pacing rapidly may  reduce the net cardiac output as the mother’s heart is  used to operate  at different  point in the  frank staling curve right  through the 10 months


Anesthetic issues in complete heart block  during cesarean section

Anesthetists have a concern here.(Genuine one of course)  A cardiologist  with a standby temporary pacemaker is  to be arranged. Cardiologist  will decide whether to have sheath or sheath plus lead  in standby mode .

Many anesthetic drugs have an adverse effect on heart rate. Drugs to be avoided are  Fentanyl ,suxamethonium, neostigmine  Induction with propofol has risk of worsening bradycardia . Controlled epidural anesthesia is preferred .This ensures slow onset anesthesia and limits hemodynamic instability.Bupivacaine is known to cause depression of heart rate .(Even with epidural route )

Miscellaneous questions

A often debated  query among obstetricians : Should I refer a CHB patient  to a cardiologist or electro-physiologist ?

There  is no  academic answer  to this question.Logic demands conservative (without compromising patient/baby  safety ) management .Electrophysiologists are rarely conservative

Radiologically how safe it  is ( for the fetus ) to undergo permanent  pacemaker implantation ?

For implanting a permanent pacemaker, about   15 minutes of  fluro time is required which could be significant .So it should be used in  exceptional situations only.

What is the effect of maternal  complete heart block on the fetal hemodynamics?

Nil or almost nil (Surprise ! surprise)



Issues during  weaning of pacing  in postpartum

Post partum period can be troublesome in few as fresh  blood volume  injected from contracting uterus.If temporary pacing has been done , it is usually possible to wean by 48 hours. Permanent pacing  is rarely required


Final message

  1. Congenital complete heart block* during pregnancy is  a well tolerated rhythm.
  2. The panic  this   entity creates is  largely unwarranted. This conclusion is derived from decades of observation by eminent clinical cardiologists.
  3. The heart  rate reserve can be estimated by a  minimal exercise test .(Atropine test with caution )
  4. Insertion of either permanent  pacemaker is not necessary* in most .
  5. If there is symptomatic hypotension /syncope during any time during pregnancy  pacemaker becomes mandatory .
  6. During labor /or cesarean section  insertion of temporary pacemaker  “may be” needed. Hence a cardiologist stand by with a temporary pacemaker  is advised to tackle any  emergency(Which is anyway  highly unlikely  !)


* This rule is applicable only in  isolated congenital CHB.  Ischemic CHB  or CHB  with associated LTGV,AV canal defects etc  need special attention.




Journal articles

The famous paper which first described safe outcome four patients with CHB in preganancy without pacemaker




anesthetic issues in pregnancy and CHB


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CHB and AV dissociation are often confused with one another . While CHB is an important cause for AVD , there are distinct differences  which have clinical implications. This table is an attempt to simpify the understanding of the two. Corections and suggestions welcome.

This is a high resolution image , to read better  right click on the table  copy image and open in any image viewer


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Sick sinus syndrome  or sinus node dysfunction (SSS, SND ) is one of the common cause of  symptomatic bradycardia .The other cause for  pathological bradycardia is complete heart block.Together , these two entities share 99% of indications for permanentpacemaker implantation.

The sinus node can get affected in various diseases . The commonest cause for SND is age related.This is manifested  as inappropriate bradycardia .The  other common presentation of  SND is exaggerated bradycardia to betablockers and calcium blockers.In fact , some consider drug  induced bradycardia  is  nothing but  , unmasking of underlying SND.Pathological states that result in SND include  hypothyrodism , infiltrative   and inflammatory diseases . (Surprisingly ,  ischemic  SND  is a lesser  clinical problem when considering  the  rampant CAD in our population )

What is  is a fundamental difference between SND and complete  heart block* ?

Sinus node is the proximal most pacemaker of the heart. When it fails the chances of  a  subsidiary pacemaker coming to the rescue is far greater than  a complete AV block. Further the quality and stability of the escape pacemaker is better in SND. In fact , in pure SND  ( With out AV nodal disease)  a sinus arrest is rarely fatal as escape rhythm  occur without fail.

* It should be emphasised  ,  there can be associated AV nodal disease in  significant (10%)  number of patients with SND .This may be present either at the  time of diagnosis or it can develop later in the course .This has important implication in the selection of   pacemaker .The discussion here is confined to isolated SND .

How common is ventricular escape rhythm in SND ?

It is very rare. the ventricle never gets a chance to come to the rescue as invariably junctional pacemaker takes over at times of extreme sinus pause/arrest.For the same reason , pause dependent VT (Brady dependent ) is also less common in SND .

What is  stokes Adam’s attack ? How  common it is  seen in SND  ?

It is the cardiogenic  syncope due  to extreme bradycardia. This classically occurs in complete heart block , when

the the escape rhythm becomes either very slow or temporarily goes for sleep .This results in a huge  pause (unlike sinus pause  of   , the pause  here is  ventricular pause  , this is  actually an  asystole  )  it  can  immediately trigger an VT or VF .

If  SND is not life threatening why pace maker is indicated in them ?

The pacemaker is primarily indicated for prevention of dizziness , near syncope or syncope.So primary impact is on improving quality of life  , not reduction in mortality. While in CHB  pacemakers improve  symptoms and survival.

Which form of SND can be dangerous ?

When SND is associated with rapid atrial fibrillation  some times it can trigger a VT/VT if ,  these patients also have

a fast accessory pathway with short refractory period. (<250msec)

Final message

If you have only one pacemaker at your disposal , but there are  two patients ,  one with SND and other with CHB please put the pacemaker to  the patient with CHB , even if the later has insurance coverage and the former is not .You are justified in  diverting  the pacemaker !

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