Fortunately, indications for DC cardioversion in pregnancy is rare. A literature search suggests only about 50 cases are reported. I haven’t shocked electively in pregnancy but occasionally have come closer to it. In this current corona lockdown period, we had a call for a potential shock in pregnant mother with fast AF, which was again avoided by the optional rate control measures.
Let us see, how often DC cardioversion might be necessary during pregnancy and few tips for its safety.
General principles
We know pregnancy can be pro arrhythmogenic. Most arrhythmias are non-sustained VPDs and APDs.They can be ignored if there is no structural heart disease, or at least postponed till delivery.
Drugs remain the mainstay.
The most common sustained arrhythmia in the young reproductive age group is SVT (AVNRT/AVRT) that can be managed with drugs like Adenosine and beta-blockers. (Flecainide/Sotalol are found to be safe in pregnancy) . Though IV Verapamil is very effective, it has with some concern for fetus, so better avoided. Please, note many of the SVTs can be reverted with simple vagal maneuvres and oral beta-blocker /Verapamil. IV Digoxin has been widely used in RHD population for AF during pregnancy.
Mind you, even Injections Adenosine, Esmolol do have bradycardic potential and need to be given in monitored setting (No surprise, they are called medical cardioversion with the attendant risk)
The universal antiarrhythmic drug Amiodarone still might come in handy in any refractory arrhythmia (Including AF) though it comes under the list of contraindication.(Safety of amiodarone in pregnancy)
One important suggestion to make. Magnesium is a wonder antiarrhythmic drug, a membrane stabilizing agent through its indirect Ca + and K + blocking properties can be a powerful antiarrhythmic agent, especially in VT. This has a unique safety profile in pregnancy.We use it in eclampsia liberally with the same action to suppress brain convulsions. (Cerebral tachycardia). Please consider IV magnesium prior to considering shock in VTs with dysfunctional ventricles as in peripartum cardiomyopathies et(Dose to 2 g in 10mL of D5W over 1 to 2 minutes)
Consider DC shock only if there is hemodynamic instability.
Hemodynamic instability demands DC version. One practical issue is , what defines hemodynamic instability? In pregnancy, the systolic BP is already in lower normal due to systemic vasodilatory state. An HR>150 makes it further fall to around 90mmhg. This tempts us to label it as unstable. In this situation, we have to rely on patients’ symptoms to define hemodynamic instability. Never try to shock a comfortable pregnant women in whatever tachycardia she is in . (Including some VTs especially from outflow, fascicular, etc ) Try to use drugs and get an expert opinion. to rule out subsets like cardiomyopathy, documented CAD, LV dysfunction.
When to shift to a cardiac facility?
This question crop up often. It is mainly logistic. May be in peripartum cardiomyopathy /Suspected ACS with VT require special care.
DC Shock checklist & Precautions
- Biphasic shocks with energy levels 100 joules ( up to 200). Ideal to give single shock, ok to err on high energy
- Pads should be well away from the abdomen.
- Synchronized with QRS complex (Machine does this)
- In an unusual event of VF and cardiac arrest Defibrillation with 300/320 J (Here unsynchronised)
- Check the crash cart ready with essential drugs.
- Keep cardiologist either on-call (Even a junior resident in labor room give immense confidence)
- Rule out LV dysfunction or significant valve disease by echo (CAD can’t be ruled out though) If echo machine is not available ask the radiology or cardiology fellow to use the abdominal USG probe to document good LV contractility and gross EF% estimate.
- If intramural thrombus is not convincingly excluded and there is AF and valvular heart disease, better to heparinse and shock to avoid embolic events.
- Temporary pacemaker support (Some of the cardioverters has transcutaneous pacing to tide over transient bradycardia that might occur post-shock)
- CPR readiness ( Extreme precaution !)
- Fetal heart monitoring and Emergency cesarian readiness.
- Finally, most important consent with patient and family.
Is electrical Insulation of baby necessary or is it possible?
It’s not required. Fetus inherently tolerates stress better. Even if, few joules reach the fetal heart inadvertently it may not mean much. What is, to be worried is maternal hypotension or bradycardia post-DC shock.
Impact on the fetus: Evidence?
The impact on fetal blood flow is not significant. This report from Taiwan reassures there is no adverse effect by measuring umbilical artery flow (Yu-Chi Wang European Journal of Obstetrics & Gynecology and Reproductive Biology 126 (2006) 268–274)
While we consider DC shock during pregnancy is safe for the fetus, still, shock pads close to the abdomen, amniotic fluid being a good conductor of electricity at least one mother showed a sustained contraction of the uterus and fetal distress. This was possibly attributable to DC shock Eleanor J. Barnes BJOG 2003 https://doi.org/10.1046/j.1471-0528.2002.02113.
Final message
Most cardiac arrhythmias in pregnancy are carefully managed by non-electrical means. Of course, emergencies can’t afford to wait. Though two lives are at stake, it’s the mother’s heart that prevails over in drug selection and risk estimation. After all, it is her loving heart, that keeps the fetus alive.
I have seen Obstetrician anxiety (which spills over to attending cardiologist too!) can be extreme in such situations. I must admit, Obstetricians, are truly sincere warriors fighting at odd hours to protect the two delicate lives. After all, taking responsibility brings the anxiety. Cardiologists must understand this and help them out in their difficult times.(without any super specialty ego !)
Reference
2.Finlay AY, Edmunds V. D.C. cardioversion in pregnancy. Br J Clin Pract. 1979;3:88–94.
Which drugs are safe?
From BMJ
Further frontiers
The DC shock from ICD experience
There have been a good number of women who got ICD for various indications (Commonly HOCM, long QT, ) who subsequently became pregnant, successfully managed during pregnancy.
(One rare study Andrea Natale et ll Circulation. 1997;96:2808–2812 documents at least 10 shock episodes documented in large series of 44 patients without any consequences)
