Supraventricular Tachycardia (SVT) is an abnormally fast heart rhythm in infants. While concerning, SVT is often treatable. Understanding this heart rhythm disorder helps parents recognize signs and ensure timely care.
What is SVT in Babies?
SVT stands for Supraventricular Tachycardia, a rapid heart rhythm originating from above the heart’s lower chambers, the ventricles. The heart relies on a precise electrical system to control its rate and rhythm. An electrical impulse starts in the sinoatrial (SA) node, the heart’s natural pacemaker, in the upper right chamber. This impulse then travels through the upper chambers (atria) and passes through the atrioventricular (AV) node before reaching the lower chambers (ventricles), ensuring a coordinated beat.
In SVT, an electrical “short circuit” or an extra electrical pathway exists, usually present from birth. This additional pathway creates an abnormal electrical loop, causing the heart to beat too quickly and bypass the normal electrical route. During an SVT episode, an infant’s heart rate can surge significantly, often exceeding 220 beats per minute (bpm), and sometimes reaching up to 300 bpm. This contrasts sharply with a normal infant heart rate, which ranges from 100-160 bpm when awake and 90-160 bpm when sleeping. While the exact cause is often unknown, SVT is typically due to this congenital extra electrical pathway, not external factors or parental actions.
Recognizing SVT in Infants
Identifying SVT in infants is challenging because symptoms are often non-specific and subtle. Babies cannot verbally communicate how they feel, so parents and caregivers must observe behavioral and physical changes carefully. These symptoms are similar to other illnesses, making early recognition dependent on close attention.
Key signs include rapid, shallow breathing or difficulty breathing, stemming from the heart’s reduced pumping efficiency. Infants might also exhibit poor feeding or refuse to feed, as the rapid heart rate can make them too tired or uncomfortable. Unusual lethargy, excessive drowsiness, or increased irritability are common indicators. Other physical signs include pale or ashen skin, increased sweating (particularly during feeding), and vomiting.
If these symptoms appear, especially in combination, prompt medical attention is important. Early recognition and intervention help prevent the heart muscle from tiring and potentially developing heart failure if an episode lasts for many hours.
How SVT is Diagnosed and Treated
When a baby is brought to medical attention with suspected SVT, healthcare providers begin with an assessment of vital signs. The primary diagnostic tool to confirm SVT is an electrocardiogram (ECG or EKG). This test records the heart’s electrical activity, providing a detailed tracing that identifies the abnormally fast rhythm and helps differentiate SVT from other conditions. It is most effective when recorded during an episode of rapid heart rate.
If SVT episodes are intermittent and not captured during a clinic visit, other diagnostic tests may be used. A Holter monitor, a portable device, continuously records the heart’s electrical activity over a period, typically 24 hours or longer, to catch sporadic episodes. An echocardiogram, which uses sound waves to create heart images, may also assess heart structure and function, ruling out any underlying structural heart conditions.
Immediate treatment for SVT in infants often begins with vagal maneuvers, which stimulate the vagus nerve to slow the heart rate. In infants, this may involve techniques like applying ice to the face for a few seconds, a procedure only performed by medical professionals or under explicit guidance. If vagal maneuvers are ineffective, medications are administered. Adenosine is a common first-line intravenous medication that temporarily interrupts the electrical short circuit and restores a normal rhythm.
Other anti-arrhythmic medications, such as beta-blockers or calcium channel blockers, may be used for ongoing management to prevent recurrence. In rare cases where other treatments fail or the baby is unstable, electrical cardioversion (a controlled electrical shock) may be necessary as an emergency measure to reset the heart’s rhythm. Infants experiencing SVT usually require hospitalization for diagnosis and initial treatment to ensure close monitoring and appropriate intervention.
Managing SVT and Long-Term Outlook
After an initial SVT episode, ongoing management involves follow-up care with a pediatric cardiologist, a doctor specializing in children’s heart conditions. Some infants may need daily medication to prevent future episodes, with dosages and types carefully adjusted as the child grows. Regular monitoring through follow-up appointments, including repeat ECGs, helps assess treatment effectiveness and detect rhythm changes.
While some babies experience only a single SVT episode, others may have recurrent episodes, particularly during infancy. Many infants outgrow the condition, often by their first birthday or early childhood, as the extra electrical pathway may become inactive or disappear. For those who continue to experience SVT, the condition is treatable, and the prognosis for most infants is excellent. With appropriate medical care and consistent follow-up, most children with SVT can lead normal, healthy lives.