- The term supraventricular tachycardia (SVT) is generally used to refer to atrioventricular nodal reentry tachycardia (AVNRT), atrioventricular reciprocating tachycardia (AVRT), and atrial tachycardia (AT) but includes any tachycardia originating at or above the atrioventricular (AV) node.
- The heart rate in SVT in infants generally ranges from 220 to 320 beats per minute (bpm) and in older children from 150 to 250 bpm.
- SVT is the most common arrhythmia in childhood.
- Incidence of SVT is 35 per 100,000 per year.
- Prevalence of SVT is 1 in 250 to 25,000 children.
- AVRT is the most common type of SVT in children, occurring in ~75% of cases.
- AVNRT rarely occurs before age 2 years.
- 50–60% of pediatric patients with SVT present in the 1st year of life.
- Most children with SVT have structurally normal hearts; however, children with congenital heart disease (CHD) have an increased risk of SVT.
- SVT is commonly observed in patients who have undergone surgery for CHD, for example, after the Mustard/Senning procedure, the Fontan operation, and repair of an atrial septal defect.
- Wolff-Parkinson-White syndrome (WPW) syndrome has been noted in several families, and an autosomal dominant (AD) mode of inheritance has been demonstrated:
- ~15% of cases of WPW have associated CHD, such as Ebstein anomaly, l-looped transposition of the great arteries, and hypertrophic cardiomyopathy.
- ~50% of the cases of junctional ectopic tachycardia (JET) occur in a familial setting with an AD mode of inheritance.
There are two major mechanisms for SVT:
- Reentry tachycardia:
- This is the most common mechanism for SVT.
- It involves a circuit rhythm within the atria (atrial flutter), within the AV node (AVNRT), or using an accessory pathway (AVRT); characterized by sudden onset and termination, regular rate, and responsiveness to pacing maneuvers and DC cardioversion
- Automatic tachycardia:
- Automaticity refers to a group of cells’ enhanced ability to spontaneously depolarize, which can overdrive suppress the sinus node.
- Examples are ectopic atrial tachycardia, multifocal atrial tachycardia, and JET; characterized by warm-up and cool-down phases, an irregular rate that is sensitive to catecholamine states, and lack of responsiveness to pacing and cardioversion
SVT can frequently be precipitated by exercise, infection, fever, or drug exposure.
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