Basics
Description
- 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.
Epidemiology
- SVT is the most common arrhythmia in childhood.
- Incidence of SVT is 35 per 100,000 per year.
- Incidence of SVT among patients with Wolff-Parkinson-White syndrome (WPW) is about 1% per year.
- Prevalence of SVT is 1 in 250 " 25,000 children.
- AVRT is the most common type of SVT in children, occurring in ’ Ό75% of cases.
- AVNRT rarely occurs before age 2 years.
- 50 " 60% of pediatric patients with SVT present in the 1st year of life.
Risk Factors
- 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.
Genetics
- WPW syndrome has been noted in several families, and an autosomal dominant (AD) mode of inheritance has been demonstrated:
- ’ Ό20% of cases of WPW have associated CHD, such as Ebstein anomaly, l-looped transposition of the great arteries, and hypertrophic cardiomyopathy.
- Many patients with the WPW pattern on electrocardiogram (ECG) do not develop SVT; when episodes of SVT do occur, the patient has WPW syndrome.
- ’ Ό50% of the cases of junctional ectopic tachycardia (JET) occur in a familial setting with an AD mode of inheritance.
Pathophysiology
There are 2 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 cell 's 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
Etiology
SVT can frequently be precipitated by exercise, infection, fever, or drug exposure.
Diagnosis
History
- Infants manifest signs and symptoms of low cardiac output and congestive heart failure (CHF) with prolonged SVT (>48 hours): tachypnea, retractions, irritability, decreased feeding, excessive sweating, hypotension, poor perfusion, and decreased urine output.
- A toddler or older child may experience palpitations, shortness of breath, chest pain, anxiety, and dizziness or syncope:
- It is important to know what the child was doing at the time the arrhythmia started and whether there is an abrupt onset and termination.
- Older children often report being able to terminate episodes of tachycardia by performing a vagal maneuver.
Physical Exam
The following need to be assessed in all patients presenting with SVT:
- Heart rate and regularity
- Respiratory rate
- Blood pressure
- Hydration status
- Peripheral perfusion
- Liver size
- Mental status
- Presence of gallop rhythm
Diagnostic Tests & Interpretation
Imaging
Initial approach
- Chest radiograph to assess for pulmonary edema and cardiomegaly
- Echocardiogram to assess underlying cardiac anatomy and ventricular function
Follow-Up Tests & Special Considerations
Repeat imaging may be warranted if there are initial abnormalities.
Diagnostic Procedures/Other
- Outpatient: Diagnosis can be made with a 24-hour or transtelephonic event monitor.
- Inpatient
- 15-lead ECG during SVT if patient is hemodynamically stable
- Continuous ECG monitoring during therapeutic maneuvers can aid in diagnosis.
- Patients with WPW pattern have ventricular preexcitation (short PR interval and a delta wave) on the ECG during sinus rhythm.
- An exercise stress test may be indicated in older patients with exercise-induced SVT or those with WPW syndrome to help determine the risk of rapid conduction through the accessory pathway.
- Electrophysiologic study is often performed to evaluate drug effect or to map in conjunction with catheter ablation.
- Nonpharmacologic maneuvers (ice, vagal) and pharmacologic maneuvers (IV adenosine) may distinguish tachycardias that involve the AV node from other types of SVT.
Differential Diagnosis
- Narrow-complex SVT needs to be distinguished from sinus rhythm and sick sinus syndrome with tachyarrhythmia.
- Structural heart disease should be excluded in all cases of newly diagnosed SVT.
- Wide-complex tachycardia can occur in the setting of SVT with bundle branch block or aberrant conduction, antegrade conduction down an accessory pathway, or preexcited atrial flutter/fibrillation in WPW. This can be difficult to distinguish from ventricular tachycardia. Unless it is known that the patient has SVT, wide-complex tachycardia should always be interpreted as ventricular tachycardia until proven otherwise.
- Differentiating between types of SVT can be accomplished by evaluating the regularity of the rate, modes of onset/termination, and the responsiveness to pacing and cardioversion.
Treatment
General Measures
- Short-term treatment goals are to terminate the tachycardia.
- Nonpharmacologic vagal maneuvers; for example, ice to the face for 15 " 30 seconds, rectal stimulation, Valsalva, gag, and headstand may be helpful. In younger children, Valsalva can be achieved by having the child blow into an obstructed straw or thumb. Pacing maneuvers via an esophageal catheter may also be used. Carotid massage and orbital pressure should not be performed in children.
- In a stable child, adenosine (rapid IV bolus, 0.1 mg/kg and increase by 0.1 mg/kg to a maximum of 0.3 mg/kg up to 12 mg) may be used to block the AV node for reentrant SVT that requires the AV node. The half-life of the drug is <10 seconds. Because of the risk of atrial fibrillation, DC cardioversion should be available. Use adenosine with caution in asthmatic patients, as it can cause acute bronchospasm.
- IV verapamil is an effective therapy in older children with SVT but should be avoided in children <12 months of age because of its vasodilatory and negative inotropic effect.
- Unstable patients with hemodynamic compromise warrant termination with synchronized DC cardioversion (0.5 " 2.0 J/kg).
- Long-term treatment goals are to reduce the frequency of episodes of SVT. Long-term treatment may not be necessary when the episodes are infrequent, self-terminating, or produce minimal symptoms.
- Catheter ablation using radiofrequency energy or cryoenergy is an alternative to long-term drug therapy and is 1st-line therapy in the following scenarios:
- SVT refractory to medical therapy
- Side effects from the medical regimen
- Patient choice due to frequency, duration, or poor quality of life
- Life-threatening arrhythmias (syncope)
- Rapid conduction properties of an accessory pathway (e.g., WPW)
- Congenital or acquired heart disease
Medication
- Long-term preventive pharmacotherapy is an alternative approach in some patients
- Reentrant SVT
- ²-Blockers (propranolol or atenolol) are 1st-line treatment in individuals with WPW and patients with exercise-induced SVT.
- Procainamide and amiodarone may be used in cases that are more resistant.
- Oral digoxin is an option in patients with hemodynamically stable SVT. Digoxin is contraindicated in patients with WPW.
- Atrial flutter may be treated with digoxin, procainamide, sotalol, or amiodarone as a single agent or in combination.
- Automatic SVT: Automatic tachycardias may be responsive to antiarrhythmics such as procainamide, flecainide (avoid if the patient has structural heart disease), amiodarone, or ²-blockers either alone or in different combinations.
Inpatient Considerations
Initial Stabilization
- Always assess the child 's ABCs (airway, breathing, and circulation).
- Initial management of SVT depends on the child 's hemodynamic condition.
Admission Criteria
- Hemodynamically unstable SVT requiring electrical cardioversion
- Tachycardia-induced cardiomyopathy
Ongoing Care
Prognosis
- Of patients who present in infancy, 30 " 70% will be asymptomatic by 1 year of age. However, ’ Ό1/3 of these patients may experience a reappearance of their tachycardia at an average age of 8 years.
- Most older children who present with SVT will have persistent recurrence of SVT.
Follow-up Recommendations
- As SVT may recur, neonates and infants have historically received maintenance therapy for the 1st year of life and then been observed off medications if they are not having breakthrough episodes of SVT. This approach has recently been challenged, and studies evaluating the ideal duration for maintenance therapy in the neonate and infant are being proposed.
- In children who present beyond infancy, spontaneous resolution of the tachycardia substrate is less likely, and treatment may need to be continued into adulthood. These patients may be considered for catheter ablation therapy.
- Over-the-counter sympathomimetic cold medications and caffeine should be avoided, as they may increase the likelihood of SVT.
Complications
Complications from SVT can arise from 1 of 3 causes:
- Persistent tachycardia can lead to CHF, tachycardia-induced cardiomyopathy, and cardiovascular collapse. This is especially true of the infant whose symptoms go unrecognized for 24 " 48 hours.
- Some patients with WPW syndrome (<5%) can have rapid conduction through the accessory pathway. A rapid ventricular response to atrial flutter/fibrillation can potentially cause ventricular fibrillation and sudden death. Therefore, digoxin and verapamil should not be used in patients with WPW syndrome.
- Side effects of pharmacologic agents used to treat SVT include bradycardia, other arrhythmias due to proarrhythmic effects (digoxin, procainamide, amiodarone, flecainide), and noncardiac side effects (GI, liver, pulmonary, and thyroid dysfunction).
Additional Reading
- Cohen MI, Triedman JK, Cannon BC, et al. PACES/HRS expert consensus statement on the management of the asymptomatic young patient with a Wolff-Parkinson-White (WPW, ventricular preexcitation) electrocardiographic pattern. Heart Rhythm. 2012;9:1006 " 1024.
- Drago F. Paediatric catheter cryoablation: techniques, successes and failures. Curr Opin Cardiol. 2008;23(2):81 " 84. [View Abstract]
- Fox DJ, Tischenko A, Krahn AD, et al. SVT: diagnosis and management. Mayo Clin Proc. 2008;83(12):1400 " 1411. [View Abstract]
- Friedman RA, Walsh EP, Silka MJ, et al. Radiofrequency catheter ablation in children with and without CHD. Pacing Clin Electrophysiol. 2002;25(6):1000 " 1017. [View Abstract]
- Manole E, Saladino RA. Emergency department management of the pediatric patient with supraventricular tachycardia. Pediatr Emerg Care. 2007;23(3):176 " 185. [View Abstract]
- Paul T, Bertram H, B Άkenkamp R, et al. Supraventricular tachycardia in infants, children and adolescents: diagnosis, and pharmacological and interventional therapy. Paediatr Drugs. 2000;2(3):171 " 181. [View Abstract]
- Sanatani S, Potts, Reed JH, et al. The study of antiarrhythmic medications in infants (SAMIS): a multicenter, randomized controlled trial comparing the efficacy and safety of digoxin versus propranolol for prophylaxis of supraventricular tachycardia in infants. Circ Arrhythm Electrophysiol. 2012;5(5):984 " 991. [View Abstract]
Codes
ICD09
- 427.89 Other specified cardiac dysrhythmias
ICD10
- I47.1 Supraventricular tachycardia
SNOMED
- 6456007 Supraventricular tachycardia (disorder)
- 276796006 Atrial tachycardia (disorder)
- 233896004 re-entrant atrioventricular node tachycardia (disorder)
FAQ
- Q: How should infants on chronic therapy be monitored?
- A: Parents with infants on chronic therapy for SVT should be educated about counting the heart rate by palpation or auscultation at least 1 or 2 times daily. This method of surveillance is just as effective as apnea/bradycardia monitors. Because alarm monitors can increase parental anxiety with frequent false alarms, they are generally not recommended. Patients on amiodarone should be monitored with liver function tests and thyroid function tests at baseline and every 3 " 6 months.
- Q: What is the concern with verapamil?
- A: Verapamil is an l-type calcium channel blocker that blocks conduction in the AV node and is very effective in treating SVT in adults. Because myocardial contractility in infants depends mostly on the trans-sarcolemmal l-type calcium channels, hypotension and cardiovascular collapse have been reported in children <1 year of age.
- Q: What are success rates and risks of catheter ablation?
- A: The success rate of radiofrequency catheter ablation varies from 80 to 97%, depending on the location of the bypass tract or ectopic focus. The incidence of major complications is <2%, with the most common being heart block requiring a pacemaker, cardiac perforation, brachial plexus injury, and embolization. The risk of complete heart block is greater in patients whose accessory pathway is located close to the AV node. In such patients, cryoablation is a safer ablation technique because of its potentially reversible electrical and thermal effect.