Fetal Tachycardia

Fetal tachycardia is when a fetus’s heart beats faster than it should. That means a heart rate of over 160 beats per minute (bpm). A normal fetal heart rate is between 120 and 160 bpm. It’s a rare condition. Experts estimate that it happens in up to 1 in 200 pregnancies.

Just like in adults, there are multiple types of fetal tachycardias. Some of the most common types include:

• Sinus tachycardia: This is when the fetus’s heart is working normally but beating faster than usual. The heart rate is typically between 180 and 200 bpm.
• Supraventricular tachycardia (SVT): In SVT, the fetus has an abnormally fast heart rate that’s over 200 bpm. This high heart rate can come from the upper heart chambers (atria) or from an abnormal electrical circuit between the upper and lower chambers. This is the most common type of fetal tachycardia.
• Atrial flutter: This is when the fetus’s upper chambers beat much faster than the lower chambers (ventricles). The overall heart rate is generally fast and sometimes irregular.
• Ventricular tachycardia: This is when the fetus’s lower heart chambers are beating too fast. This is rare.

Symptoms of fetal tachycardia

Fetal tachycardia doesn’t cause symptoms that the mother can notice or feel. Healthcare providers usually find it while listening to the fetus’s heartbeat directly or during an ultrasound exam.

Fetal tachycardia causes

The causes of fetal tachycardia vary by type.

Sinus tachycardia can happen for many reasons. Some come from conditions affecting the mother. Others come from conditions affecting the fetus. Some of the most likely causes include:

• Fever in the mother: This is the most likely cause. Sometimes, fetal tachycardia even starts before the mother’s fever does.
• Infections: These can be in either the fetus or the mother. One of the more likely examples is chorioamnionitis.
• Hypoxia: A fetus’s heart will speed up when it isn’t getting enough oxygen or is in distress.
• Medicines the mother takes while pregnant: Examples include medicines for low blood pressure, asthma and COPD, and stimulant medicines for ADHD, narcolepsy and obesity.
• Health conditions in the mother: Examples include anemia and high thyroid hormone levels.

SVT, atrial flutter and ventricular tachycardia all happen because of issues with the fetal heart’s electrical system.

Complications of this condition

Fetal sinus tachycardia doesn’t cause complications. Other forms of fetal tachycardia don’t cause complications if they only last a short time (minutes or less). But the underlying cause of the fetus’s tachycardia may still need treatment.

Fetal tachycardia also usually isn’t severe when it doesn’t happen often and the fetus’s heart rate is under 200 bpm. But when a fetus has tachycardia for a long time, complications can happen and may be severe. They include:

• Fetal hydrops
• Heart damage (cardiomyopathy) and heart failure
• Fetal compromise or stillbirth

Complications are more likely when the tachycardia heart rate:

• Is very fast and/or lasts a long time
• Starts earlier during the pregnancy
• Happens along with a structural heart condition

How doctors diagnose this condition

There are several tools that healthcare providers can use to diagnose and monitor fetal tachycardia, including:

• Fetal echocardiogram: This specialized form of ultrasound is the most common way providers can detect and monitor fetal tachycardia. It lets providers evaluate the heart’s rate and rhythm.
• Fetal electrocardiogram: This detects the fetus’s heart through the skin of the mother’s abdomen. It’s normal for changes during pregnancy to interfere with detecting heart activity. That’s why this works well during early pregnancy but loses effectiveness later on, which is when most fetal tachycardias occur.
• Fetal heart rate monitoring: There are external and internal forms of this. The external form uses sensors on the mother’s skin. The internal form uses a sensor on the fetus’s scalp inside the uterus, and this is only used during delivery.

How is fetal tachycardia treated?

For sinus tachycardia or another tachycardia that happens only for very short parts of the day, treatment usually isn’t necessary. In those cases, your provider will recommend close monitoring.

But if the fetus’s heart rate is over 200 bpm or lasts for a good portion of the day, or the fetus shows signs of complications like fetal hydrops, your provider will recommend aggressive treatment.

When treatment is necessary, the first approach is to use anti-arrhythmia medications, which can reset or slow down the fetus’s heart rate. Providers give these medicines to the mother because they can pass through the placenta during pregnancy and lower the fetus’s heart rate.

In some cases, providers may need to give medication to a fetus directly. But this is rare, and providers usually only do it when other treatment options don’t work.

The most common medications for fetal tachycardia include:

• Digoxin
• Flecainide
• Sotalol
• Amiodarone

The specific type of fetal tachycardia helps guide providers in choosing which medicines to use. Sometimes, a combination of medicines is best. Other factors contribute, too, like whether the fetus shows signs of hydrops or heart failure.

In most cases, an early delivery is not the goal. But if you’re pretty close to your due date already or the tachycardia can’t be treated well with the medications, early delivery may be the best option. That would involve inducing labor or doing a cesarean section.

Each of the possible approaches can vary depending on many different factors. Your healthcare provider can explain which options are likely to help you and the fetus the most.

What can I expect with fetal tachycardia?

Fetal tachycardia can be scary, but most fetuses do well. Fetuses with just sinus tachycardia or short, occasional tachycardia will only need follow-up. All others will need referral to a specialist and treatment.

Giving medication to the mother successfully treats fetal tachycardia in most cases. But treatment is key. Some babies won’t have tachycardia after birth and may not need medication. Others will continue to have tachycardia and need ongoing care. A pediatric cardiologist will evaluate and guide this treatment after birth.

Most mothers can tolerate the medications needed to treat the fetus. A cardiologist and obstetric specialist will monitor you during treatment. You may also need EKGs and blood tests to make sure the medicines are safe for you.

What are the long-term effects of fetal tachycardia?

About half of babies who had fetal tachycardia will have tachycardia after birth, though in many babies it only lasts six to 12 months. Newborns with tachycardia may need further treatment. That can include medications, surgery or other approaches. Your child’s provider can explain treatment options and offer recommendations.