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 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 Recognition ±Drugs (patient/family choice) Digoxin generally contraindicated Risk stratification 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 Danger of ventricular fibrillation Persistent prolonged SVT 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 Synchronized (avoids making worse) 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 Can be curative 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)