Cardiac Arrhythmia


The information provided below is for readers based in the United States of America. Readers outside of the United States of America should seek the information from local sources.

What is cardiac arrhythmia during pregnancy?

An arrhythmia, or cardiac arrhythmia, is an abnormality with the rate or the rhythm of the heart, meaning that the heartbeat is too slow, too fast and/or irregular. There are various categories of arrhythmia, each of which is further divided into different subtypes.

A bradyarrhythmia (bradycardia) is an abnormally slow heartbeat, meaning that the heart rate is below 60 beats per minute (bpm). Bradycardia also is called heart block. If the heartbeat is just a little too slow and signals are conducted normally from the hearts atria to the ventricles, its called 1st-degree heart block, and it is not harmful. In 2nd-degree heart block, there is a problem in the conduction of signals from a pacemaker called the atrioventricular (AV) node through a conduction system that normally stimulates the ventricles to contract at an optimal moment subsequent to atrial contraction that maximizes the hearts efficiency. The delay causes problems in the rhythm between the contraction of the atria and the contraction of the ventricles. In 3rd-degree heart block, also called complete heart block (CHB), there is no conduction of signals at all through the AV node, so there is no coordination at all between the atria and ventricles; the atria beat when they want, and the ventricles beat when they want, and they beat at a slow rate.

Generally, more of an issue for pregnancy, are the tachyarrhythmias, or tachycardia, which is any disturbance that includes a rapid heartbeat, meaning a heart rate that is higher than the normal rate of the heart during rest (as opposed to during exercise). For an adult, this means a heart rate that is more than 100 bpm. This can be part of a normal process during pregnancy, as the heart rate in pregnant women normally increases by about 25 percent. Since many women have a resting heart rate of around 80 bpm, the normal increase in heart rate over the course of pregnancy can take you into the range of 100 bpm when you are resting, such that technically you have a tachyarrhythmia, while you feel perfectly normal. This is called sinus tachycardia, because it results from the hearts natural pacemaker, called the sinoatrial (SA) node, simply beating faster than it usually does, causing the hearts two atria to contract as signals also reach the AV node, which acts as a kind of relay station that normally signals ventricles to contract at the optimal time. As long as the AV node is getting impulses only from the SA node, and as long as the ventricles are contracting only due to impulses relayed by the AV node, the heart has a normal rhythm, known as sinus rhythm. On an electrocardiogram (ECG), your doctor can recognize this normal rhythm by the presence of a P wave (indicating contraction of the atria) occurring within a particular time range before what is called a QRS complex (indicating contraction of the ventricles), with one P wave for every QRS, without changes in the relation between these two features even if the rate of the heartbeat is fast (or slow).

As you may imagine, there are many categories of tachyarrhythmia apart from sinus tachycardia. Such tachyarrhythmias are categorized based on whether its the atria or ventricles beating too quickly and based on what is triggering the rapid beat. Most such tachyarrhythmias fall into a broad category called supraventricular tachyarrhythmia (SVT), because the problem is coming from above the ventricles. SVTs include tachyarrhythmias of the atria and certain tachyarrhythmias of the ventricles. Additionally, there is a category called ventricular tachycardia (VT or v-tach), which is the worst kind of tachycardia, but fortunately is rare in pregnancy.

Apart from sinus tachycardia, which is not dangerous, the two most common types of arrhythmia in pregnancy are two types of SVT called AV nodal reentrant tachycardia (AVNRT) and atrioventricular reciprocating tachycardia (AVRT). When this results from what is called an ectopic pacemaker (a concentration of stimulating heart muscle cells that is not supposed to be there) getting and causing episodes of sudden, intense tachyarrhythmia just once in a while, the condition is called paroxysmal SVT (PSVT).

One other kind of cardiac arrhythmia that can affect women of childbearing age is an inherited disorder called congenital long-QT syndrome (LQTS).

How common is cardiac arrhythmia during pregnancy?

Sinus tachycardia is present in most pregnant women, but is not clinically important, since it is not dangerous. Bradyarrhythmias are very rare, but SVT is present in about 24 per 100,000 patients who are admitted to the hospital, so SVT is the most common cardiac arrhythmia in women of reproductive age. About 20 percent of pregnant women have an SVT that was diagnosed previously, and that is exacerbated by the pregnancy. The risk of developing SVT increases as pregnancy progresses. The commonality of particular types of SVT varies in pregnancy. 

How is cardiac arrhythmia during pregnancy diagnosed?

Cardiac arrhythmia is diagnosed with ECG and also with Holter monitoring. Both are non-invasive procedures that work through electrodes that are attached to your skin. In ECG, electrodes are attached to your arms, leg, and chest. In some cases, additional sites, to provide your family doctor, obstetrician, and cardiologist with detailed information of the hearts electrical activity from numerous angles to detect problems in different regions of the heart. This is done in the doctors office or the hospital. With Holter monitoring, the principle is the same as ECG, but you are fitted with a device that you wear for a day or more while you go about your normal activities. Various types of Holter monitors are available with varying numbers of electrodes, depending on how much detail is needed concerning different parts of your heart. In all cases, however, unlike ECG, the Holter monitor records data constantly and transmits those data to your doctor (or the data are downloaded when you return to the doctor). Consequently, if some electrical event happens just once in a while, your doctors can see it.

If ECG or Holter shows that you merely have sinus tachycardia, doctors may also run tests for some common conditions, other than pregnancy, that cause the SA node to work too quickly and that are common in young to middle-aged women. Such conditions include anemia and an overactive thyroid, both of which can be diagnosed with blood tests and also can be unmasked by pregnancy.

Does cardiac arrhythmia cause problems during pregnancy?

Sinus tachycardia is not harmful, nor is 1st-degree bradycardia, so long as you dont have a problem with the blood supply to the heart muscle (ischemia), which is very uncommon among women of reproductive age. But these situations can be a warning sign of some underlying problem, such as anemia, a thyroid disorder, generalized anxiety disorder, panic attack disorder, certain heart infections, and certain heart attacks.

A potential consequence of an SVT episode is what doctors call hemodynamic instability, meaning that the cardiovascular system is unstable and potentially can collapse, leading to a substantial drop in blood pressure, which could lead you to pass out. If you suffer from LQTS, there is a possibility that it can lead to a potentially fatal form of VT, called torsades de pointes. The term LQTS refers to when the time it takes from when the ventricles change electrically to contract until they recover electrically
called the QT interval takes longer than it is supposed to take. However, pregnancy itself is known to do the opposite, which is to shorten the QT interval. Thus, it is thought that pregnancy may reduce the danger if you have LQTS, but there is increased danger in the postpartum period.

As for arrhythmias of the atria, the most common and concerning type is atrial fibrillation (AF), the danger of which is that you will generate emboli (traveling clots) that will reach the brain or lungs.

Does cardiac arrhythmia during pregnancy cause problems for the baby?

A heart block, or an SVT episode, or a VT episode that destabilizes your cardiovascular system, can put the health and life of the fetus at risk by causing a reduction of blood circulation through the uterus and placenta. If you have LQTS, there is a risk that your baby may have it too, and there may be a risk of sudden infant death syndrome, particularly if there is fetal distress leading to an urgent need for cesarean delivery.

What to consider about taking medications when you are pregnant or breastfeeding:

  • The risks to yourself and your baby if you do not treat the cardiac arrhythmia
  • The risks and benefits of each medication you use when you are pregnant
  • The risks and benefits of each medication you use when you are breastfeeding

What should I know about using medication to treat my cardiac arrhythmia during pregnancy?

There are a variety of medications given to treat various cardiac arrhythmias. The choice depends on what type of arrhythmia it is because different arrhythmias are caused by abnormalities in different parts of the heart, which in turn are affected by different medications. Among the available medications for each arrhythmia type, a particular antiarrhythmic drug called dronedarone must be avoided during pregnancy because it is known to harm the fetus. Another antiarrhythmic drug called amiodarone, which doctors try to avoid using in pregnancy because it may harm the fetal thyroid, slow the fetal heart, and cause growth restriction and preterm birth, can be given under special circumstances, namely if the mother is in great danger, and this drug is the only way to stabilize her heartbeat. Other antiarrhythmic drugs, such as procainamide and flecainide, are not known to be harmful.

The first choice medication to treat an episode of PSVT is called adenosine, which slows conduction of electrical signals through the heart, especially at the AV node. Given intravenously, adenosine is extremely safe in pregnancy, because it disappears from the mothers bloodstream in a matter of seconds, before it has time to reach the fetus. To treat an SVT for the long-term, and also to treat an attack if two tries of adenosine do not work, doctors can give you a type of drug called a beta-blocker, such as propranolol, metoprolol, or labetalol. Beta-blockers also are the main treatment for LQTS and are an option for sinus tachycardia, if your doctor decides that your heart rate should be slowed, and no underlying problem is detected. The beta-blockers listed above are considered relatively safe during pregnancy.

As for AF, this is treated with drugs against platelets (such as aspirin), drugs against clot formation (blood thinners, including warfarin, heparin, and similar medications), drugs that slow the heart (beta-blockers), and antiarrhythmic drugs. Warfarin is dangerous to the embryo and fetus during certain times in pregnancy, but it can be used during other parts of pregnancy if the need is great. Low molecular weight heparin (LMWH) is often used as an alternative to heparin, for all or part of pregnancy, plus there is another type of heparin called unfractionated heparin (UH). Generally, it is a big trade-off between managing the risk of clots versus managing the risk to the baby. 

Who should NOT stop taking medication for cardiac arrhythmia during pregnancy?

Any pregnant woman who experiences an SVT attack should receive adenosine, or another drug to stop the attack, due to the risk of cardiovascular collapse. If you are taking an anti-arrhythmic drug on a long term basis, the decision on whether to continue with a drug and/or replace it with a different drug must involve your cardiologist and often also an obstetrician who specializes in high-risk pregnancies.

What should I know about choosing a medication for my cardiac arrhythmia during pregnancy?

You may find Pregistrys expert reports about the medications to treat this condition here. Additional information can also be found in the sources listed below.

What should I know about taking a medication for my cardiac arrhythmia when I am breastfeeding?

Propranolol, metoprolol, and labetalol are considered safe during breastfeeding as there is minimal absorption into the breastmilk. Adenosine given to a mother is not dangerous to the nursing infant since it disappears very rapidly from the mothers blood. Neither warfarin (used in North American for long-term anticoagulation therapy) nor a similar drug called acenocoumarol (used in Europe) enter breastmilk or otherwise affect a nursing infant. Thus, once you have delivered, warfarin therapy can be added or added back. LMWH does enter breastmilk, but in very tiny amounts and is not harmful because it is degraded in the infants digestive system (LMWH is not taken orally for this reason, but must be injected or infused).

What alternative therapies besides medications can I use to treat cardiac arrhythmia during pregnancy?

Various types of SVT are treated effectively, with a permanent cure, with a technique called ablation, in which a specially-trained cardiologist guides instruments through tubes through your blood vessels to the site of the ectopic pacemaker and destroys it. This procedure can be administered safely during pregnancy. A short-term treatment that often can end an SVT episode in an emergency is vagus nerve stimulation. This can be achieved by massaging the carotid area of the neck, or by dipping the womans head partly in cold water. If you have an SVT episode that cannot be stabilized, a cesarean section may become necessary. In some cases of cardiac arrhythmia, doctors may need to shock your heart with electrical current to correct the rhythm. In other cases, doctors may need to use special instruments to destroy certain pathways in your heart that are conducting electrical signals where they should not go.

What can I do for myself and my baby when I have cardiac arrhythmia during pregnancy?

Cooperate with your physicians. If medications are recommended, or other procedures are needed to stabilize your condition, keep in mind they are generally safe.

Resources for cardiac arrhythmia in pregnancy:

For more information about cardiac arrhythmia during and after pregnancy, contact (800-994-9662 [TDD: 888-220-5446]) or contact the following organizations:


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Last Updated: 28-12-2019
General information

It is very common for women to worry about having a miscarriage or giving birth to a child with a birth defect while they are pregnant. Many decisions that women make about their health during pregnancy are made with these concerns in mind.

For many women these concerns are very real. As many as 1 in 5 pregnancies end in a miscarriage, and 1 in 33 babies are born with a birth defect. These rates are considered the background population risk, which means they do not take into consideration anything about the health of the mom, the medications she is taking, or the family history of the mom or the baby’s dad. A number of different things can increase these risks, including taking certain medications during pregnancy.

It is known that most medications, including over-the-counter medications, taken during pregnancy do get passed on to the baby. Fortunately, most medicines are not harmful to the baby and can be safely taken during pregnancy. But there are some that are known to be harmful to a baby’s normal development and growth, especially when they are taken during certain times of the pregnancy. Because of this, it is important to talk with your doctor or midwife about any medications you are taking, ideally before you even try to get pregnant.

If a doctor other than the one caring for your pregnancy recommends that you start a new medicine while you are pregnant, it is important that you let them know you are pregnant.

If you do need to take a new medication while pregnant, it is important to discuss the possible risks the medicine may pose on your pregnancy with your doctor or midwife. They can help you understand the benefits and the risks of taking the medicine.

Ultimately, the decision to start, stop, or change medications during pregnancy is up to you to make, along with input from your doctor or midwife. If you do take medications during pregnancy, be sure to keep track of all the medications you are taking.