Neonatal Supraventricular Tachycardia (SVT) refers to a condition where a newborn’s heart beats abnormally fast. This rapid heart rhythm, an arrhythmia, originates in the upper chambers of the heart. In newborns with SVT, the heart rate can often exceed 220 beats per minute, which is considerably faster than a typical newborn’s normal heart rate. Neonatal SVT is frequently manageable and is the most common type of sustained fast heart rhythm observed in infants.
Understanding Neonatal SVT
The heart’s rhythm is controlled by electrical signals that travel through its chambers. Normally, these signals originate in the sinus node, a specialized area in the right atrium, and then spread through the atria, causing them to contract. The signal then travels through the atrioventricular (AV) node and down to the ventricles, ensuring efficient blood circulation.
In neonatal SVT, an electrical problem in the heart’s upper chambers disrupts this normal pathway, causing the heart to beat too quickly. This usually stems from an extra electrical pathway or a “short circuit” within the heart formed during the baby’s development. This additional pathway can create a re-entry circuit, where electrical impulses loop back, causing the heart to beat at very high rates.
Identifying Neonatal SVT
Recognizing neonatal SVT can be challenging because newborns cannot verbally express discomfort. Parents might observe signs such as unusual irritability, fatigue, poor feeding, or vomiting. Other symptoms can include rapid breathing (tachypnea) or a pale appearance. Parents might also notice visible pulsations in the baby’s neck or chest due to the fast heart rate. If these symptoms persist for several hours or days, they could progress to signs of heart failure.
Diagnosis of SVT involves a clinical assessment and an electrocardiogram (ECG). An ECG records the heart’s electrical activity to identify the fast rhythm and its origin. For intermittent symptoms, a Holter monitor may be used. This portable device records the heart’s rhythm continuously over 24 hours or longer, helping capture episodes not occurring during a clinical visit.
Managing Neonatal SVT
Immediate management of neonatal SVT focuses on restoring a normal heart rhythm. Initial interventions may include vagal maneuvers, which stimulate the vagus nerve to slow the heart rate. One technique involves applying an ice pack to the baby’s face for a few seconds, but this should only be performed under strict medical guidance.
If vagal maneuvers are not effective, medications are often used. Adenosine, administered intravenously, is a common first-line medication for SVT because it temporarily blocks electrical conduction through the AV node, interrupting the fast rhythm. Its effects are very short-lived. Other medications, such as beta-blockers (e.g., propranolol) or calcium channel blockers, may be used to control the heart rate or prevent recurrence. Verapamil, a calcium channel blocker, is generally avoided in infants under 12 months due to the risk of severe hypotension.
For long-term management, maintenance medications are frequently prescribed to prevent future episodes. Propranolol is often a preferred choice for prophylactic treatment, though other antiarrhythmic drugs like flecainide or amiodarone may also be used. The goal is to keep the heart rate regular until the condition potentially resolves on its own. Catheter ablation, a procedure that targets and eliminates the extra electrical pathway, is rarely performed in neonates due to potential complications and lower success rates in this age group, but it may be considered later in life if medications are ineffective.
Long-Term Care and Prognosis
The long-term outlook for infants diagnosed with neonatal SVT is generally positive when the condition is properly managed. Many cases of SVT in infants, particularly those due to an accessory pathway, resolve spontaneously as the child grows, often by 12 to 18 months of age. This spontaneous resolution is believed to occur as the heart matures and the accessory pathways become inactive.
Despite the potential for spontaneous resolution, ongoing monitoring is typically recommended. This often includes regular check-ups with a pediatric cardiologist to assess heart rhythm and overall cardiac health. Parents may also be instructed on how to monitor their baby’s heart rate at home, such as by counting the pulse on the chest daily.
While a significant number of infants will outgrow their SVT, there is a possibility of recurrence, with rates ranging from 22% to 55% in infants. Recurrence risk can vary depending on factors such as the presence of Wolff-Parkinson-White syndrome or if the SVT was diagnosed later in infancy. However, for most infants, appropriate medical management leads to a good prognosis, allowing them to lead healthy, active lives.