Supraventricular Tachycardia in Children

Introduction to Supraventricular Tachycardia in Children

Supraventricular Tachycardia (SVT) is the most common sustained arrhythmia in children, characterized by a rapid heart rate originating from tissue at or above the bundle of His. It affects approximately 1 in 250 to 1 in 1000 children, with a peak incidence in infancy and another in adolescence.

SVT in children can occur in structurally normal hearts or in association with congenital heart defects. Early recognition and appropriate management are crucial, as prolonged episodes can lead to hemodynamic compromise, particularly in infants.

Pathophysiology of Supraventricular Tachycardia

The pathophysiology of SVT involves abnormal electrical impulse generation or conduction within the atria or atrioventricular (AV) junction. The mechanisms can be broadly categorized into:

  1. Reentry: The most common mechanism in children, involving a circular electrical pathway
    • Atrioventricular Reentrant Tachycardia (AVRT): Utilizes an accessory pathway
    • Atrioventricular Nodal Reentrant Tachycardia (AVNRT): Involves dual AV node physiology
  2. Automaticity: Enhanced automatic firing from ectopic foci
    • Atrial Ectopic Tachycardia (AET)
    • Junctional Ectopic Tachycardia (JET)
  3. Triggered Activity: Afterdepolarizations leading to repeated firing

The specific mechanism influences the clinical presentation, ECG findings, and management approach.

Classification of Supraventricular Tachycardia in Children

SVT in children can be classified based on the mechanism and anatomical origin:

  1. Atrioventricular Reentrant Tachycardia (AVRT)
    • Orthodromic AVRT (most common)
    • Antidromic AVRT
    • Permanent Junctional Reciprocating Tachycardia (PJRT)
  2. Atrioventricular Nodal Reentrant Tachycardia (AVNRT)
    • Typical (slow-fast)
    • Atypical (fast-slow or slow-slow)
  3. Atrial Ectopic Tachycardia (AET)
  4. Junctional Ectopic Tachycardia (JET)
    • Congenital JET
    • Postoperative JET
  5. Atrial Flutter
  6. Atrial Fibrillation (rare in children)

The age of the child often correlates with the likely mechanism, with AVRT being most common in infants and young children, while AVNRT becomes more prevalent in older children and adolescents.

Clinical Presentation of Supraventricular Tachycardia in Children

The clinical presentation of SVT in children varies widely, depending on the child's age, the duration of the episode, and the underlying cardiac function. Common presentations include:

  • Infants:
    • Irritability or fussiness
    • Poor feeding or vomiting
    • Pallor or cyanosis
    • Tachypnea or respiratory distress
    • Signs of heart failure in prolonged episodes
  • Older children and adolescents:
    • Palpitations
    • Chest pain or discomfort
    • Dizziness or lightheadedness
    • Syncope (rare)
    • Fatigue or exercise intolerance

The onset of SVT is typically sudden, and episodes can last from a few seconds to several hours or even days. Hemodynamic compromise is more likely in infants and young children, especially with prolonged episodes.

Diagnosis of Supraventricular Tachycardia in Children

Diagnosing SVT in children involves a combination of clinical assessment and electrocardiographic evaluation. Key diagnostic steps include:

  1. Clinical history:
    • Frequency and duration of symptoms
    • Triggers (e.g., exercise, stress)
    • Associated symptoms
    • Family history of arrhythmias or sudden death
  2. Physical examination:
    • Assessment of vital signs and hemodynamic status
    • Evaluation for signs of underlying heart disease
  3. 12-lead ECG during tachycardia:
    • Regular, narrow-complex tachycardia (usually)
    • Heart rate typically > 220 bpm in infants, > 180 bpm in children
    • Analysis of P wave morphology and relationship to QRS
  4. Additional diagnostic tools:
    • Holter monitor or event recorder
    • Exercise stress test
    • Echocardiogram to evaluate cardiac structure and function
    • Electrophysiology study in selected cases

Differential diagnosis includes sinus tachycardia, ventricular tachycardia, and other causes of narrow-complex tachycardias. Accurate diagnosis is crucial for appropriate management and long-term follow-up.

Management of Supraventricular Tachycardia in Children

Management of SVT in children depends on the hemodynamic stability of the patient, the specific type of SVT, and the frequency of episodes. The approach can be divided into acute management and long-term prevention:

Acute Management:

  1. Vagal maneuvers:
    • Ice to the face in infants
    • Valsalva maneuver or diving reflex in older children
  2. Pharmacological cardioversion:
    • Adenosine (first-line pharmacological therapy)
    • Beta-blockers (e.g., esmolol)
    • Calcium channel blockers (in older children)
  3. Electrical cardioversion: For hemodynamically unstable patients
  4. Overdrive pacing: In specific situations, especially postoperative SVT

Long-term Management:

  1. Observation: For infrequent, well-tolerated episodes
  2. Chronic pharmacological therapy:
    • Beta-blockers (e.g., propranolol, atenolol)
    • Class IC antiarrhythmics (e.g., flecainide)
    • Class III antiarrhythmics (e.g., amiodarone, sotalol)
  3. Catheter ablation:
    • Considered for older children with frequent episodes or drug-refractory SVT
    • Radiofrequency ablation or cryoablation

Management should be individualized based on the child's age, SVT mechanism, frequency of episodes, and associated cardiac conditions. Parent and patient education about recognition and management of SVT episodes is crucial.

Prognosis of Supraventricular Tachycardia in Children

The prognosis for children with SVT is generally favorable, with several factors influencing the long-term outlook:

  • Age at onset: SVT in infants often resolves spontaneously by age 1 year, while onset in older children may persist
  • Underlying mechanism: Some forms (e.g., AVRT due to accessory pathways) may resolve with age, while others (e.g., AVNRT) tend to persist
  • Presence of structural heart disease: May complicate management and affect overall prognosis
  • Response to treatment: Most children respond well to medical management or ablation procedures

Long-term considerations include:

  • Risk of recurrence: Varies depending on the SVT mechanism and management approach
  • Need for ongoing medication: Some children may require long-term antiarrhythmic therapy
  • Impact on quality of life: Most children with well-controlled SVT can participate in normal activities
  • Risk of sudden cardiac death: Extremely low in children with SVT and structurally normal hearts

Regular follow-up is important to assess for recurrence, monitor for medication side effects, and adjust management strategies as the child grows. With appropriate management, the vast majority of children with SVT have an excellent long-term prognosis.

Atrioventricular Reentrant Tachycardia (AVRT)

AVRT is the most common form of SVT in children, particularly in infants and young children.

Mechanism:

  • Involves an accessory pathway between the atria and ventricles
  • Orthodromic AVRT (most common): Antegrade conduction through AV node, retrograde through accessory pathway
  • Antidromic AVRT (rare): Antegrade conduction through accessory pathway, retrograde through AV node

Clinical Features:

  • Sudden onset and termination of tachycardia
  • Heart rates typically 220-300 bpm in infants, 180-250 bpm in children
  • May be associated with Wolff-Parkinson-White (WPW) syndrome

ECG Characteristics:

  • Orthodromic: Narrow complex tachycardia, retrograde P waves (often hidden in QRS)
  • Antidromic: Wide complex tachycardia, may be mistaken for ventricular tachycardia
  • WPW pattern on resting ECG: Short PR interval, delta wave, wide QRS complex

Management:

  • Acute: Vagal maneuvers, adenosine
  • Long-term: Beta-blockers, class IC antiarrhythmics, catheter ablation
  • Special consideration for WPW: Avoid AV nodal blocking agents in atrial fibrillation

Prognosis:

Generally good, with many cases resolving spontaneously by age 1 year. Catheter ablation has high success rates in older children.

Atrioventricular Nodal Reentrant Tachycardia (AVNRT)

AVNRT is the second most common form of SVT in children, more prevalent in older children and adolescents.

Mechanism:

  • Involves dual AV node physiology with a slow and a fast pathway
  • Typical (slow-fast) AVNRT: Antegrade conduction through slow pathway, retrograde through fast pathway
  • Atypical (fast-slow or slow-slow) AVNRT: Less common variants

Clinical Features:

  • Sudden onset of rapid, regular palpitations
  • Heart rates typically 180-250 bpm
  • May experience neck pulsations due to cannon a-waves

ECG Characteristics:

  • Narrow complex tachycardia
  • Retrograde P waves often hidden within or just after QRS complex
  • Typical AVNRT: Short RP interval
  • Atypical AVNRT: Long RP interval

Management:

  • Acute: Vagal maneuvers, adenosine
  • Long-term: Beta-blockers, calcium channel blockers (in older children), catheter ablation

Prognosis:

Generally good, but tends to be more persistent than AVRT. Catheter ablation has high success rates with low risk of AV block in experienced centers.

Atrial Ectopic Tachycardia (AET)

AET is less common than AVRT and AVNRT but can be more challenging to manage.

Mechanism:

  • Enhanced automaticity from an ectopic focus in the atria
  • Can be unifocal or multifocal

Clinical Features:

  • Often presents with incessant tachycardia
  • May lead to tachycardia-induced cardiomyopathy if prolonged
  • Variable heart rates, typically 120-250 bpm

ECG Characteristics:

  • Narrow complex tachycardia
  • P waves precede each QRS complex, with morphology different from sinus P waves
  • Variable AV conduction (1:1 or AV block)
  • Warm-up and cool-down phenomenon may be observed

Management:

  • Acute: Often resistant to adenosine
  • Long-term: Beta-blockers, class IC or III antiarrhythmics
  • Catheter ablation for drug-refractory cases

Prognosis:

Can be challenging to control medically. Risk of tachycardia-induced cardiomyopathy if inadequately treated. May resolve spontaneously in some cases.

Junctional Ectopic Tachycardia (JET)

JET is a relatively rare form of SVT in children, occurring in two distinct settings: congenital and postoperative.

Mechanism:

  • Enhanced automaticity from the AV junction
  • Congenital form: Idiopathic or associated with familial disorders
  • Postoperative form: Following cardiac surgery involving manipulation near the AV node

Clinical Features:

  • Congenital JET: Often presents in infancy with incessant tachycardia
  • Postoperative JET: Typically occurs within 24-48 hours after cardiac surgery
  • Heart rates usually 180-300 bpm

ECG Characteristics:

  • Narrow complex tachycardia
  • AV dissociation with ventricular rate faster than atrial rate
  • Retrograde VA conduction may be present (1:1 or variable)

Management:

  • Acute: Cooling, sedation, electrolyte optimization
  • Pharmacological: Amiodarone, procainamide, or ivabradine
  • Other measures: Atrial overdrive pacing, ECMO in severe cases

Prognosis:

Congenital JET can be difficult to control and may require combination therapy. Postoperative JET usually resolves within days but can cause significant morbidity.

Atrial Flutter

Atrial flutter is less common in children but can occur, especially in those with structural heart disease or after cardiac surgery.

Mechanism:

  • Macro-reentrant circuit in the atria, typically around the tricuspid annulus
  • Can be typical (counterclockwise) or atypical

Clinical Features:

  • May present with palpitations, fatigue, or heart failure symptoms
  • Atrial rates typically 250-350 bpm
  • Often associated with variable AV conduction (2:1, 3:1, etc.)

ECG Characteristics:

  • Saw-tooth flutter waves, best seen in leads II, III, aVF
  • Regular atrial rate with variable ventricular response
  • Typical flutter: Negative flutter waves in inferior leads

Management:

  • Acute: Synchronized cardioversion, overdrive pacing
  • Pharmacological: Class III antiarrhythmics (e.g., amiodarone)
  • Long-term: Catheter ablation for recurrent cases

Prognosis:

Generally good with appropriate management. Risk of recurrence depends on underlying cardiac status.

Atrial Fibrillation

Atrial fibrillation is rare in children but can occur, especially in those with underlying heart disease or certain genetic conditions.

Mechanism:

  • Chaotic, rapid electrical activity in the atria
  • Multiple micro-reentrant circuits

Clinical Features:

  • Uncommon in children with structurally normal hearts
  • May be associated with cardiomyopathies, channelopathies, or post-surgical states
  • Symptoms can include palpitations, fatigue, and reduced exercise tolerance

ECG Characteristics:

  • Irregularly irregular rhythm
  • Absence of distinct P waves, replaced by fibrillatory waves
  • Variable ventricular rate, often rapid if untreated

Management:

  • Acute: Cardioversion if hemodynamically unstable
  • Rate control: Beta-blockers, calcium channel blockers
  • Rhythm control: Class III antiarrhythmics, cardioversion
  • Anticoagulation: Consider in prolonged episodes or with risk factors

Prognosis:

Depends on underlying cause. May be challenging to manage long-term. Importance of addressing any underlying cardiac conditions.



Objective QnA: Supraventricular Tachycardia in Children
  1. Question: What is the definition of supraventricular tachycardia (SVT) in children? Answer: Supraventricular tachycardia is defined as an abnormally rapid heart rhythm originating above the ventricles, typically with a rate > 220 beats per minute in infants or > 180 beats per minute in children.
  2. Question: Which is the most common mechanism of SVT in children? Answer: Atrioventricular reentrant tachycardia (AVRT) using an accessory pathway is the most common mechanism of SVT in children.
  3. Question: What is the typical ECG appearance of atrioventricular nodal reentrant tachycardia (AVNRT)? Answer: AVNRT typically presents with a narrow QRS complex tachycardia with absent or retrograde P waves, often visible as pseudo-R' waves in lead V1 or pseudo-S waves in inferior leads.
  4. Question: Which congenital heart defect is associated with an increased risk of SVT in children? Answer: Ebstein's anomaly of the tricuspid valve is associated with an increased risk of SVT, particularly Wolff-Parkinson-White syndrome.
  5. Question: What are the common presenting symptoms of SVT in infants? Answer: Infants with SVT may present with irritability, poor feeding, tachypnea, or signs of heart failure. Older children may complain of palpitations, chest pain, or dizziness.
  6. Question: Which vagal maneuver is most effective in terminating SVT in infants? Answer: The diving reflex, elicited by applying an ice pack to the face, is often the most effective vagal maneuver in infants.
  7. Question: What is the first-line pharmacological treatment for acute SVT in children? Answer: Adenosine is the first-line pharmacological treatment for acute SVT in children due to its rapid onset and short half-life.
  8. Question: Which medication is commonly used for chronic suppression of SVT in children? Answer: Beta-blockers, such as propranolol or atenolol, are commonly used for chronic suppression of SVT in children.
  9. Question: What is the role of catheter ablation in managing SVT in children? Answer: Catheter ablation is considered for children with frequent or severe SVT episodes, those with medication-refractory SVT, or when there is a patient/family preference for definitive treatment.
  10. Question: Which type of SVT is associated with the Wolff-Parkinson-White syndrome? Answer: Orthodromic atrioventricular reentrant tachycardia (AVRT) is the most common type of SVT associated with Wolff-Parkinson-White syndrome.
  11. Question: What is the significance of the delta wave on ECG in children with SVT? Answer: The delta wave indicates ventricular pre-excitation and suggests the presence of an accessory pathway, as seen in Wolff-Parkinson-White syndrome.
  12. Question: Which imaging modality is useful in diagnosing structural heart disease associated with SVT in children? Answer: Echocardiography is useful in diagnosing structural heart disease that may be associated with SVT in children.
  13. Question: What is the typical heart rate range for atrial flutter in infants? Answer: Atrial flutter in infants typically presents with atrial rates of 300-500 beats per minute, often with 2:1 conduction resulting in ventricular rates of 150-250 beats per minute.
  14. Question: Which antiarrhythmic medication should be avoided in patients with Wolff-Parkinson-White syndrome and atrial fibrillation? Answer: Digoxin should be avoided in patients with Wolff-Parkinson-White syndrome and atrial fibrillation, as it can enhance conduction through the accessory pathway and potentially precipitate ventricular fibrillation.
  15. Question: What is the role of Holter monitoring in evaluating children with suspected SVT? Answer: Holter monitoring can help document the frequency and duration of SVT episodes, assess the efficacy of treatment, and identify asymptomatic events in children with suspected SVT.
  16. Question: Which electrophysiological study finding confirms the diagnosis of AVNRT? Answer: The presence of dual AV nodal physiology and inducible tachycardia with concurrent atrial and ventricular activation confirms the diagnosis of AVNRT during electrophysiological study.
  17. Question: What is the typical ECG appearance of atrial ectopic tachycardia in children? Answer: Atrial ectopic tachycardia typically presents with an abnormal P wave morphology, variable P-P intervals, and gradual onset and termination ("warm-up" and "cool-down").
  18. Question: Which complication is associated with long-standing, uncontrolled SVT in children? Answer: Tachycardia-induced cardiomyopathy can develop in children with long-standing, uncontrolled SVT, leading to dilated cardiomyopathy and heart failure.
  19. Question: What is the role of flecainide in managing SVT in children? Answer: Flecainide is a Class IC antiarrhythmic agent that can be used for chronic suppression of SVT in children, particularly those with AVRT or atrial ectopic tachycardia.
  20. Question: Which non-invasive test can help differentiate between narrow complex tachycardias in children? Answer: Adenosine administration during continuous ECG recording can help differentiate between various narrow complex tachycardias by revealing the underlying atrial activity.
  21. Question: What is the significance of intermittent pre-excitation on ECG in children? Answer: Intermittent pre-excitation suggests that the accessory pathway has a relatively long refractory period, which may indicate a lower risk of rapid conduction during atrial fibrillation.
  22. Question: Which surgical procedure for congenital heart disease is associated with an increased risk of postoperative atrial tachycardias? Answer: The Fontan procedure for single ventricle physiology is associated with an increased risk of postoperative atrial tachycardias.
  23. Question: What is the role of transesophageal pacing in managing SVT in children? Answer: Transesophageal pacing can be used for both diagnostic purposes (to induce SVT) and therapeutic purposes (to terminate SVT) in children, particularly when other methods have failed.
  24. Question: Which type of SVT is most likely to spontaneously resolve in infants? Answer: SVT due to a concealed accessory pathway (orthodromic AVRT) is most likely to spontaneously resolve in infants, often by one year of age.
  25. Question: What is the significance of fetal tachycardia detected during pregnancy? Answer: Fetal tachycardia, often due to SVT, can lead to hydrops fetalis and fetal demise if untreated, necessitating close monitoring and potential in-utero treatment.
  26. Question: Which medication is preferred for acute termination of SVT in children with poor ventricular function? Answer: Amiodarone is often preferred for acute termination of SVT in children with poor ventricular function, as it has less negative inotropic effect compared to other antiarrhythmic drugs.
  27. Question: What is the role of cardioversion in managing SVT in children? Answer: Synchronized electrical cardioversion is reserved for hemodynamically unstable SVT or when pharmacological methods have failed to terminate the arrhythmia.
  28. Question: Which complication is associated with radiofrequency catheter ablation near the AV node? Answer: Inadvertent AV block is a potential complication of radiofrequency catheter ablation near the AV node, particularly when treating AVNRT or septal accessory pathways.
  29. Question: What is the typical ECG appearance of permanent junctional reciprocating tachycardia (PJRT) in children? Answer: PJRT typically presents as a narrow complex tachycardia with retrograde P waves visible in the ST segment, often with a long RP interval (RP > PR).


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