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What is a fetal arrhythmia and how is it treated?
Fetal arrhythmia refers to an abnormal fetal heartbeat or rhythm. Most arrhythmias are not dangerous, but some are concerning. If your doctor suspects fetal arrythmia, you need to consult a fetal cardiologist immediately. At Texas Children’s Fetal Center, we have treated fetal arrhythmias for decades, and have strategies to manage the various types. With proper intervention, most arrhythmias can be resolved before birth, and the children will go on to live happy, healthy lives.
What causes an arrhythmia?
The rhythm of the heart is controlled by the sinus node (known as the pacemaker of the heart) and the atrioventricular node (AV node). The sinus node is in the right atrium, and the AV node is in the middle of the heart, between the atria and ventricles. In a normal rhythm, the sinus node sends a signal to the AV node, the AV node responds by prompting the ventricles to contract, resulting in a heartbeat. Then the heart relaxes and the process starts over again.
If this process is disrupted, the heart may beat too fast (tachycardia) or too slow (bradycardia). In most cases, the cause of the disruption is unknown, but it can result from an electrolyte imbalance, inflammation or medication. In rare cases, it may be related to a congenital heart defect. We treat all forms of arrhythmia at Texas Children’s—from the most common to the extremely rare.
Let’s talk about the more typical conditions.
PACs—common and not dangerous
A premature atrial contraction, or PAC, is by far the most common arrhythmia we see. In PACs, extra heartbeats can come from the top of the heart, separate from the sinus node. These extra beats try to signal the AV node, which sometimes works (called “conducted”) and sometimes does not (called “nonconducted”). If the PACs are conducted, the ventricles have extra contractions, and this sounds like intermittent extra heart beats. If the PACs are nonconducted, this can cause short intermittent slowing of the heart beat while the heart recovers; this may sound like an intermittent slow heart rate.
Majority of PACs, both conducted and nonconducted, pose no threat to your baby, and usually resolve over time without intervention. In some cases, however, we will monitor your baby and advise mom to reduce caffeine and stress. It is very uncommon for PACs to turn into supraventricular tachycardia (a more serious arrhythmia, see below), but a child may need further treatment when extra heartbeats increase and come in rapid succession.
Another type of arrythmia we treat quite often is supraventricular tachycardia, or SVT. With SVT, the heart beats too fast, either because of an abnormal connection between the top and bottom of the heart, or many extra heartbeats coming from the top of the heart. When the top of the heart (the atrium) starts beating very rapidly (usually >300 beats per minute), this type of SVT is referred to as atrial flutter.
If your baby stays in SVT for a prolonged time, there is danger of heart failure or hydrops (accumulation of fluid) and treatment is necessary. Typical treatment is oral anti-arrhythmic medicine taken by mom which is carried across the placenta to the fetus.
At the beginning of the medication, mom will need to stay at the hospital where we monitor her with labs, EKG, and possibly an echocardiogram. We also follow baby closely as well, to make sure their heart rhythm is slowed to a safe rate. Sometimes, if your baby is close to term, we will go ahead and deliver.
SVT typically resolves before or after birth, either by itself or with medical therapy. Sometimes treatment is needed during the first year or so of life, and for a small number of patients, beyond their first year. If SVT goes away in the fetus or in the first year of life, it may return again around puberty.
In rare cases, the patient may need treatment for several years. If treatment is still needed for recurrent SVT around the age of 8 or 9, a catherization procedure can usually correct it permanently.
What does a heart block mean?
Another rhythm we cautiously watch for is heart block. A condition where the sinus node and the AV node are not communicating very well. Heart block can quickly progress into complete heart block, a more dangerous condition, where there is no communication at all between the sinus and AV node. Complete heart block is usually permanent.
The most common cause of heart block is when mom is carrying antibodies associated with lupus or Sjogren’s syndrome (autoimmune conditions). These antibodies can cause inflammation in the fetal heart, blocking the AV node’s ability to react to the sinus node. As antibody levels rise, the baby is at an increased risk for complete heart block. We monitor this condition by fetal echocardiography to determine if the atria and ventricles are communicating with each other. Steroids can sometimes be used to slow the progression to complete heart block when antibodies are the cause, but the results are not conclusive. We are currently involved in a research study investigating home monitoring, home ultrasound and whether or not early administration of steroids is effective.
Heart block can also be associated with some congenital heart diseases including congenitally-corrected transposition of the great arteries and heterotaxy (abnormal arrangement of organs in the chest and abdomen). In these cases, heart block is related to a structural issue, not a signaling problem, and cannot be treated with steroids.
Most babies with complete heart block will eventually need a pacemaker. This can be performed during the newborn period if necessary. Most babies, however, can wait until they are a little older and stronger.
What’s the prognosis?
Texas Children’s Fetal Center has a long and successful history of treating babies with abnormal heart rhythms and other fetal heart conditions. For babies with PACs, we provide effective monitoring and reassurance that the problem will resolve. With SVT, we are usually able to stop or slow the rhythm before the baby is born, providing proper care for both mom and baby. If the child does need care after birth for SVT or heart block, our Electrophysiology Team at Texas Children’s Heart Center provides world class care and monitoring for these children—from birth into adulthood. With proper intervention, most babies with arrhythmias can live full and normal lives.