Beta-Blockers and Baby

Dr Specialist,
I have recently been disgnosed with partial right sided bundle branch block from an ECG trace, and am due to have an Eco and Holter monitor test in a weeks time, as per my cardiologist (which I have only just been referred to by my OBGYN). My concern is that the cardiologist wants me to start taking beta blocker "Minax" (metoprolol) before he even has the results back from these tests. I am almost 37 weeks gestation now, and have regular episodes of palpations and tachycardia daily. I do not get dizzy, or feel faint, nor do I get chest pain. I am concerned about the effects of the drug on the baby, as I have read it lowers resp rate, HR, BP & Sugars, as well as decreasing spontaneous respirations at birth in the baby. I have read the drug should be stopped 3-4 days pre labour (which I would like to know how we would know that date? as there is no elective birth planned). I am feeling I should request an early casearian (39 weeks) or an induction (if there is no risk of me cardiac arresting) and then start the drugs. I am scared of putting my baby at risk i.e. RDS etc. or having a still born due to altering its haemodynamics.
Would you mind please telling me what real effects I should be concerned or not concerned about with taking this drug.
Please provide an in depth medical explaination if you can, as both my husband and I have medical backgrounds, but not with paediatric pharmacology.
Thank you for any assistance with this if you can. I have read many journals etc. and they almost all advise against beta blockers in the final stages of gestation.
With kind regards,
K

[Bridget A. Hewitt, RN]

I think you might do better posting this question in the Pregnancy expert forum.  The Pediactric Heart forum is for questions regarding heart issues/problems in children. Good luck

[Jeffrey R Boris, M.D.]

Dear K,

Overall, beta blockers can cause some growth arrest in fetuses, and can slow the heart rate some, though typically not enough to cause the heart to stop or adversely altering hemodynamic function.  They are frequently used when the fetus has an arrhythmia, such as one called supraventricular tachycardia.  We do have a fair bit of experience with this medication in fetuses, and it is overall reasonably tolerated.  I will say that 2-3 weeks of exposure won’t likely cause a problem for your baby.  With routine monitoring, it could be stopped if your baby was showing problems with growth, which would be the most likely complication seen.  Finally, I wouldn’t necessarily recommend a schedule caesarian section if there isn’t a good medical indication for it.

More importantly, though, I’m not exactly sure why you are being put on a beta blocker for “partial right bundle branch block,” especially when you are asymptomatic.  Having not evaluated you, I can’t say for sure what is being seen and what the concerns are.  That said, we frequently see what we refer to as incomplete right bundle branch block as a normal variant in pediatric and adolescent patients quite frequently.  It typically does not require treatment, unless there are other abnormal findings, such as an atrial septal defect or an arrhythmia.  

I do agree with Bridget, our nurse who does the screening for our forum, that you might also get some good assistance in the Pregnancy expert forum.  You also might want to post the same question to the adult Cardiology forum, as well.

[Kez09]

Thank you so very much Doctor, and for the recommendations by yourself and nurse Bridget.
I really appreciate all the help you have given me,
With Kind Regards,
Keri