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
- Congenital complete heart block* during pregnancy is a well tolerated rhythm.
- The panic this entity creates is largely unwarranted. This conclusion is derived from decades of observation by eminent clinical cardiologists.
- The heart rate reserve can be estimated by a minimal exercise test .(Atropine test with caution )
- Insertion of either permanent pacemaker is not necessary* in most .
- If there is symptomatic hypotension /syncope during any time during pregnancy pacemaker becomes mandatory .
- 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 !)
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* This rule is applicable only in isolated congenital CHB. Ischemic CHB or CHB with associated LTGV,AV canal defects etc need special attention.
References
Books
Journal articles
The famous paper which first described safe outcome four patients with CHB in preganancy without pacemaker
http://medind.nic.in/iad/t06/i1/iadt06i1p43.pdf
http://www.joacp.org/index.php?option=com_journal&task=check_subscription&id=1077
anesthetic issues in pregnancy and CHB
Dr.S.Venkatesan MD 
