1. Supraventricular Tachycardia in Infancy and Childhood
Terrence Chun, MD
Pediatric Electrophysiology and Pacing

2. Cardiac electrical anatomy

3. SVT - Overview
Rapid rhythm that involves or is driven by structures in the upper heart
Incidence up to 1:250 children
Generally well-tolerated, even fast rates
Risk of life-threatening arrhythmias is uncommon

4. Narrow vs. Wide QRS
Not all narrow QRS complex tachycardia is supraventricular tachycardia
Not all wide QRS complex tachycardia is ventricular tachycardia

5. SVT Mechanisms - Overview
Reentrant rhythms
Automatic rhythms

6. SVT mechanisms – Automatic Rhythms
Originate from a particular focus
“Warm-up” and “cool-down” behavior
Respond to drugs and maneuvers that affect myocardial automaticity
May be suppressed by faster rates
Usually do not respond to cardioversion (typically pause, then restart)

7. SVT mechanisms – Automatic Rhythms
Left atrial focus
2:1 AVN conduction

8. SVT mechanisms – Reentrant rhythms
Requires a “circuit” of tissue to create repetitive activation
Must have appropriate conditions to perpetuate reentrant rhythm
Usually abrupt onset and termination
Regular, with little variation in rate
Often will respond to cardioversion

9. SVT mechanisms – Reentrant rhythms

10. Diagnostic methods 12-lead electrocardiogram ! ! !
Post-op atrial/ventricular pacing wires
Esophageal pacing leads
Adenosine can be diagnostic
Invasive electrophysiology study

11. Diagnostic methods Always
Always record a rhythm strip during any intervention (adenosine, cardioversion, Valsalva, etc.)

12. Diagnostic methods
Record a rhythm strip

13. ECG clues to diagnosis Wide vs. narrow complex Regular vs. irregular
Abrupt vs. gradual
P wave relationship to QRS

14. Parade of Rhythms
Automatic Arrhythmias

15. Automatic rhythms – Sinus Tachycardia
Sinus node – fish-shaped structure with “head” at SVC-RA junction and “tail” extending along RA wall
S-tach usually due to increased sympathetic discharge, fever, anemia, hypovolemia, hyperthyroidism, etc.
Inappropriate sinus tachycardia - rare

16. Automatic rhythms – Sinus TachycardiaDx
Rate greater than normal range, but usually less than 200
P wave axis normal (0 ~ +90°)
PR interval normal Tx
Treat the cause

17. Automatic rhythms – Automatic Atrial Tachycardia
Originates from a focus in either the right or left atrium, or atrial septum
Commonly from atrial appendages, crista terminalis, pulmonary veins
Can also be due to central lines, etc.
Also called “ectopic atrial tachycardia”
although any automatic rhythm other than sinus rhythm is technically “ectopic”

18. Automatic rhythms – Automatic Atrial TachycardiaDx
Speeds-up and slows-down, rates vary
P wave axis abnormal
PR interval may be abnormal (it is a function of distance from focus to AVN)
May see 2° AV block (e.g. Wenckebach or 2:1 at higher atrial rates)
Adenosine  P waves “march through” despite AV block

19. Automatic rhythms – Automatic Atrial Tachycardia

20. Automatic rhythms – Automatic Atrial TachycardiaTx
Remove source (check CXR and pull back PICC)
Beta-blockers
Esmolol infusion in ICU setting
propranolol, atenolol
Amiodarone, others
Catheter ablation

21. Automatic rhythms – Junctional Tachycardia
Originates from around the AV junction
Also called “JET” (Junctional Ectopic Tachycardia), because it sounds cool
Rate
Most commonly seen post-operatively, usually self-limited
Congenital forms, more persistent

22. Automatic rhythms – Junctional TachycardiaDx
AV dissynchrony
Sinus P wave at different rate than narrow QRS
Atrial wire ECG (in post-op with pacing wires)
“Cannon a-waves” on CVP monitor
Retrograde P waves (abnormal Pw axis)
May be on top, before, or after QRS

23. Automatic rhythms – Junctional Tachycardia
Cannon a-waves

24. Automatic rhythms – Junctional TachycardiaTx
Reduce catecholamines
Decrease inotropic drips
Pain control and sedation
Cooling/hypothermia
Drugs (amiodarone)
ECMO
Catheter ablation(?)

25. Parade of Rhythms
Reentrant Arrhythmias

26. Reentrant rhythms – Pathway Mediated Tachycardia
Bypass tract of conductive tissue connects atrium to ventricle
Most common mechanism of SVT in children
Rate
May be “manifest” (e.g. WPW) or concealed (no preexcitation)
Pathway can be anywhere on mitral or tricuspid annuli, usually left-sided

27. Reentrant rhythms – Pathway Mediated Tachycardia
Orthodromic reciprocating tachycardia
“Runs correctly” with normal conduction
Down AV node (narrow QRS)
Up accessory pathway (retrograde)
Retrograde P waves may be visible after QRS
Antidromic reciprocating tachycardia
“Runs against” normal conduction
Down accessory pathway (wide QRS)
Up AV node (retrograde)
Less common

28. Reentrant rhythms – Pathway Mediated TachycardiaDx
Electrocardiogram
Rhythm strips of start and stop of SVT

29. Reentrant rhythms – Pathway Mediated TachycardiaTx
Valsalva maneuvers, Ice to face
Adenosine (technique matters!)
Antiarrhythmic drugs
Beta blockers (watch blood glucose in infants!)
Digoxin (limited value; digitalization only in difficult situations)
Others (Verapamil, Flecainide, Sotolol, etc.)
Catheter ablation

30. Reentrant rhythms – Wolff-Parkinson-White Syndrome
Electrocardiogram findings
Short PR interval
Wide QRS complex
Delta wave

31. Reentrant rhythms – Wolff-Parkinson-White Syndrome

32. Reentrant rhythms – Wolff-Parkinson-White Syndrome
Clinical symptoms
Palpitations
SVT
Note narrow QRS and lack of delta wave!

33. Reentrant rhythms – Wolff-Parkinson-White Syndrome
Sudden death(!)
Atrial fibrillation
Rapid conduction over bypass tract
Ventricular fibrillation
Risk % per year

34. Reentrant rhythms – Wolff-Parkinson-White SyndromeTx
Tachycardia control
Recognition
±Drugs (patient/family choice)
Digoxin generally contraindicated
Risk stratification
Holter
Exercise testing
Invasive electrophysiology testing
Catheter ablation

35. Reentrant rhythms – AV Node Reentry Tachycardia
More common in teens and adults
Tachycardia circuit contained within atrioventricular node
Activates atria at the “top” of the circuit, ventricles at “bottom” of circuit, nearly simultaneously
Rate
Usually cannot see retrograde P waves

36. Reentrant rhythms – AV Node Reentry Tachycardia

37. Reentrant rhythms – AV Node Reentry TachycardiaTx
Adenosine
Cardioversion
±Pharmacotherapy
Beta blockers
Digoxin
Others
Catheter ablation

38. Reentrant rhythms – Atrial Flutter
“Flutter” circuit around anatomic structures in atrium
Eustachian valve
Crista terminalis
Fossa ovalis
Surgical incisions

39. Reentrant rhythms – Atrial Flutter
Atrial rate ~300 (higher in neonates)
Ventricular rate depends on AV node conduction
1:1  300/min
2:1  150/min
3:1  100/min
May be 3:1 then 2:1 then…

40. Reentrant rhythms – Atrial Flutter
Sawtooth “flutter” waves (may or may not be helpful)

41. Reentrant rhythms – Atrial FlutterDx
Electrocardiogram
Adenosine blocks AV node; flutter waves continue Tx
Rate control – digoxin, beta blockers, etc.
Overdrive pacing
DC cardioversion
Catheter ablation

42. Threatening Rhythms Atrial fibrillation in high-risk WPW
Danger of ventricular fibrillation
Persistent prolonged SVT
Tachycardia induced cardiomyopathy (reversible)
SVT in compromised cardiac status
Syncope or cardiovascular collapse

43. Treatment Pearls

44. Adenosine 0.1-0.4 mg/kg/dose Very short half-life (seconds)
Central administration can be helpful, but not necessary
Rapid saline bolus (5-10 ml) essential
Stopcock on venous access is helpful

45. DC Cardioversion Dose Synchronized (avoids making worse)
Cardioversion J/kg
Defibrillation 1-2 J/kg
Synchronized (avoids making worse)
Paddles – front+apex
Patches
Front+apex
Front+back

46. Catheter Ablation Multiple catheters Size limitations Can be curative
Ideally > 15 kg, but can be done in infants if necessary
Can be curative
~95% success rate in children

47. Record a Rhythm Strip! Especially during interventions
Most SVT in infants and children is hemodynamically well-tolerated
Proper diagnosis can guide appropriate therapy
RA/LA/RL/LL limb leads give 6 electrograms (I, II, III, aVL, aVR, aVF)