Supraventricular Tachycardia
in Infancy and Childhood
Terrence Chun, MD
Pediatric Electrophysiology and Pacing
Cardiac electrical anatomy
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

Narrow vs. Wide QRS
Not all narrow QRS complex tachycardia
is supraventricular tachycardia
 Not all wide QRS complex tachycardia is
ventricular tachycardia

SVT Mechanisms - Overview
Reentrant rhythms
 Automatic rhythms

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)

SVT mechanisms –
Automatic Rhythms
Left atrial focus
 2:1 AVN conduction

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

SVT mechanisms –
Reentrant rhythms
Diagnostic methods
12-lead electrocardiogram ! ! !
 Post-op atrial/ventricular pacing wires
 Esophageal pacing leads
 Adenosine can be diagnostic
 Invasive electrophysiology study

Diagnostic methods
Always
 Always
 Always record a rhythm strip during
any intervention (adenosine,
cardioversion, Valsalva, etc.)

Diagnostic methods

Record a rhythm strip
ECG clues to diagnosis
Wide vs. narrow complex
 Regular vs. irregular
 Abrupt vs. gradual
 P wave relationship to QRS

Parade of Rhythms
Automatic Arrhythmias
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

Automatic rhythms –
Sinus Tachycardia

Dx
Rate greater than normal range, but
usually less than 200
 P wave axis normal (0 ~ +90°)
 PR interval normal


Tx

Treat the cause
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”
Automatic rhythms –
Automatic Atrial Tachycardia

Dx
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

Automatic rhythms –
Automatic Atrial Tachycardia
Automatic rhythms –
Automatic Atrial Tachycardia

Tx
Remove source (check CXR and pull back
PICC)
 Beta-blockers

Esmolol infusion in ICU setting
 propranolol, atenolol

Amiodarone, others
 Catheter ablation

Automatic rhythms –
Junctional Tachycardia
Originates from around the AV junction
 Also called “JET” (Junctional Ectopic
Tachycardia), because it sounds cool
 Rate 170-200+
 Most commonly seen post-operatively,
usually self-limited
 Congenital forms, more persistent

Automatic rhythms –
Junctional Tachycardia

Dx

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
Automatic rhythms –
Junctional Tachycardia

Cannon a-waves
Automatic rhythms –
Junctional Tachycardia

Tx

Reduce catecholamines
Decrease inotropic drips
 Pain control and sedation

Cooling/hypothermia
 Drugs (amiodarone)
 ECMO
 Catheter ablation(?)

Parade of Rhythms
Reentrant Arrhythmias
Reentrant rhythms –
Pathway Mediated Tachycardia





Bypass tract of conductive tissue connects
atrium to ventricle
Most common mechanism of SVT in children
Rate 180-240
May be “manifest” (e.g. WPW) or concealed
(no preexcitation)
Pathway can be anywhere on mitral or
tricuspid annuli, usually left-sided
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
Reentrant rhythms –
Pathway Mediated Tachycardia

Dx
Electrocardiogram
 Rhythm strips of start and stop of SVT

Reentrant rhythms –
Pathway Mediated Tachycardia

Tx
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
Reentrant rhythms –
Wolff-Parkinson-White Syndrome

Electrocardiogram findings
Short PR interval
 Wide QRS complex
 Delta wave

Reentrant rhythms –
Wolff-Parkinson-White Syndrome
Reentrant rhythms –
Wolff-Parkinson-White Syndrome

Clinical symptoms
Palpitations
 SVT


Note narrow QRS and lack of delta wave!
Reentrant rhythms –
Wolff-Parkinson-White Syndrome

Sudden death(!)
Atrial fibrillation
 Rapid conduction over bypass tract
 Ventricular fibrillation
 Risk 0.1-0.6% per year

Reentrant rhythms –
Wolff-Parkinson-White Syndrome

Tx

Tachycardia control




Risk stratification




Recognition
±Drugs (patient/family choice)
Digoxin generally contraindicated
Holter
Exercise testing
Invasive electrophysiology testing
Catheter ablation
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 200-250
 Usually cannot see retrograde P waves

Reentrant rhythms –
AV Node Reentry Tachycardia
Reentrant rhythms –
AV Node Reentry Tachycardia

Tx
Adenosine
 Cardioversion
 ±Pharmacotherapy

Beta blockers
 Digoxin
 Others


Catheter ablation
Reentrant rhythms –
Atrial Flutter

“Flutter” circuit
around anatomic
structures in atrium
Eustachian valve
 Crista terminalis
 Fossa ovalis
 Surgical incisions

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…

Reentrant rhythms –
Atrial Flutter

Sawtooth “flutter” waves (may or may
not be helpful)
Reentrant rhythms –
Atrial Flutter

Dx
Electrocardiogram
 Adenosine blocks AV node; flutter waves
continue


Tx
Rate control – digoxin, beta blockers, etc.
 Overdrive pacing
 DC cardioversion
 Catheter ablation

Threatening Rhythms

Atrial fibrillation in high-risk WPW


Persistent prolonged SVT


Danger of ventricular fibrillation
Tachycardia induced cardiomyopathy
(reversible)
SVT in compromised cardiac status

Syncope or cardiovascular collapse
Treatment Pearls
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

DC Cardioversion

Dose
Cardioversion 0.25-1 J/kg
 Defibrillation 1-2 J/kg

Synchronized (avoids making worse)
 Paddles – front+apex
 Patches

Front+apex
 Front+back

Catheter Ablation
Multiple catheters
 Size limitations



Ideally > 15 kg, but can be done in infants
if necessary
Can be curative

~95% success rate in children
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)
