Many different vagal maneuvers have been used to convert stable supraventricular tachycardia (SVT). The procedures are relatively simple and can be performed by a variety of medical personnel, including physicians, physicians-in-training, nurses, and paramedics. However, because these techniques may in rare instances result in profound bradycardia or asystole, supervision by individuals experienced in pediatric resuscitation is recommended when the procedures are performed in medical settings. Vagal maneuvers are usually temporary measures to re-establish normal sinus rhythm, because medication is often required to maintain the child in this rhythm.

SVT is an abnormal tachycardia, usually due to a re-entrant mechanism, which is narrow complex (of the QRS) in about 90% of cases. In older children and adolescents, SVT is often present at rates above 150 beats per minute (bpm). In infants, the heart rate is usually at or above 240 bpm but may be as high as 300 bpm. SVT must be distinguished from sinus tachycardia (ST), which is usually less than 200 bpm but can occasionally produce heart rates of up to 265 bpm in infancy. However, signs of fever, hypovolemia, or sepsis usually are coexistent (1,2). It is important to distinguish SVT from ventricular tachycardia (VT). In general, the patient with wide complex tachycardia in the range of 150 to 240 bpm must have an assessment to determine whether there is a risk factor for VT, such as cardiac disease, an electrolyte abnormality, or a poisoning from overdose. If a past history of recurrent SVT is indicated, it is usually safe to assume the patient is again in SVT.

SVT is the most common significant dysrhythmia in children. Its incidence ranges from 1:1,000 to as high as 1:250. The majority of children presenting with SVT will be under 1 year of age, and close to half of the cases will occur in infants less than 4 months of age. These young babies usually have a normal underlying heart, although there will occasionally be a predisposing factor such as myocarditis, congenital heart disease, thyrotoxicosis, or infection/sepsis (2). Of note, many infants will present with SVT after receiving an over-the-counter cold preparation or other medication with sympathomimetic properties.

Most pediatric patients with SVT that is not associated with a specific cause (medication overuse, etc.) have an accessory atrioventricular (AV) pathway. This developmental abnormality may change the heart’s electrophysiologic characteristics during the child’s growth (1). At birth, autonomic cardiovascular control is not fully developed and may be under hormonal control. This concept of autonomic imbalance or immaturity is one hypothesis of why SVT is more common in young infants (3). SVT from AV node re-entry or primary atrial tachycardia is more common after infancy or postcardiac surgery (1).

Parasympathetic stimulus via the vagus nerve to the sinus and AV nodes slows heart rate. At birth, the infant has a predominance of vagal tone due to an immature sympathetic system. However, despite this parasympathetic predominance, few vagal maneuvers are usually successful in converting SVT
in young children, with the exception of the diving reflex (bradycardia following submersion or ice water to the forehead) (3). The diving reflex, which occurs in many aquatic mammals and also in young children, is a very potent stimulus to the afferent limb of this vagally mediated reflex (4).

Vagal maneuvers should be used only in children with SVT who do not exhibit signs of hemodynamic compromise. Patients with severe congestive heart failure or shock should have immediate cardioversion (see Chapter 23) (5). With stable SVT, vagal maneuvers often are tried first. If unsuccessful, IV adenosine is then used (Fig. 70.1) (5).

Consultation with a pediatric cardiologist is warranted for all children with SVT, even after an uncomplicated return to sinus rhythm. Vagal maneuvers may only be effective temporarily. Furthermore, additional diagnostic workup may be needed, including electrophysiologic studies, and long-term medical treatment is often indicated.