An interesting case of Supraventricular Tachycardia in a late preterm neonate

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The mother is a 21-year-old G1P0, who presented to the OB triage after an incidental finding of fetal tachycardia(>200s) of unknown etiology at 36 weeks gestational age. Prenatal laboratories were negative for syphilis, Hepatitis B, HIV, and GBS. OB team proceeded with an emergency C section. The baby was apneic, requiring PPV for a minute, and then was transitioned to CPAP in the OR. The patient admitted to NICU for HR>200.

Physical Exam:

Vitals: Temp: 36.8, HR: 230, RR: 40, Saturation: 94% on nasal cannula 1L, BP:  56/38. Physical examination is normal except for mild subcostal retractions.


EKG done on admission were concerning for SVT (Figure 1). Chest X-ray showed signs of pulmonary congestion. 


The patient was given adenosine 0.1 mg/kg X 2 with no response, and the dose was increased to 0.15 mg/kg X 1 with no response. EKG was concerning for atrial flutter then; the patient was symptomatic with increased work of breathing and low systolic blood pressure. Synchronized cardioversion was done with conversion to normal sinus rhythm (Figure 2). Patient transferred to cardiac ICU. 

Echocardiogram showed decreased right and left ventricular systolic function. He was started on milrinone infusion. In the setting of decreased ventricular function, IV digoxin started in order to prevent any possible recurrence of arrhythmia and allowing his myocardium to recover. Milrinone infusion was stopped at 24 hours. Repeat echocardiogram showed the normal systolic function of both the ventricles. He was discharged home on a maintenance dose of oral digoxin for 3 months with cardiology follow up. 

Final Diagnosis:

Supraventricular tachycardia


The incidence of neonatal arrhythmias is 1-5%. It can be due to abnormal impulse generation or abnormal impulse propagation. Also, it can be benign (PAC, PVC, Junctional rhythm) or non-benign (VT, SVT, AV conduction abnormalities, LQTS). 


-    Neonatal tachyarrhythmia

-    Neonatal bradyarrhythmia

-    Premature contractions

Neonatal tachyarrhythmia:

•    The heart rate is usually more than 100. 

•    Mechanism of action (MOA): Re-entry or increased automaticity. 

•    Common classification: Supraventricular tachycardia(SVT), Atrial flutter, Ventricular tachycardia

•    SVT types:  Atrioventricular re-entrant tachycardia (AVRT), Atrioventricular nodal re-entrant tachycardia (AVNRT), permanent form of junctional reciprocating tachycardia (PJRT), ectopic atrial tachycardia(EAT), junctional ectopic tachycardia (JET)

Supraventricular tachycardia:


     -    P waves follow QRS

     -    Associated with WPW in term neonates, not in preterm infants

     -    Upstroke/Delta waves present

     -    Accessory pathways related to reentrant SVT

     -    Treatment: IV adenosine is commonly used. Other drugs used in neonates are procainamide or amiodarone

     -    Maintenance drugs must be used to prevent recurrence; Digoxin/Propranolol commonly used.  


     -    Uncommon in neonates

     -    Mechanism of action: Fast/slow pathway surrounding the AV node

     -    P waves not visible; super-imposed on QRS axis.

     -    Treatment same as AVRT


    -    Mechanism of action: Slow conducting retrograde accessory pathway

    -    Present with incessant tachycardia

    -    Lower ventricular rate(~200) -- > Longer RP interval

    -    Refractory to medical management. 

    -    Most of the cases require maintenance therapy/RF ablation.

    -    If untreated, can lead to tachycardia-induced cardiomyopathy


   -    Abnormal P wave axis

   -    Present with 1:1 AV conduction

   -    Resistant to Adenosine/DC conversion

   -    Treatment: Flecainide + Amiodarone or Flecainide + Sotalol    


    -    Ectopic focus at or near AV node

    -    Enhanced automaticity of the AV junction

    -    Common in post-op CHD neonates

    -    Treatment: Amiodarone, ablation, permanent pacing

Atrial flutter:

    -    Uncommon type of fetal and neonatal cardiac arrhythmia

    -    Etiology is unknown in most cases

    -    Mechanism of action: Macroreentry within the atrial wall; sawtooth flutter waves with an atrial rate of up to 500/min in leads 2,3 and aVF

    -    Atrial flutter usually presents with 2:1 AV conduction

    -    AV block doesn't terminate conduction; adenosine used to unmask hidden P waves

    -    Treated with DC version or trans-esophageal pacing

    -    Recurrence is uncommon. Long term therapy with digoxin/propranolol not needed

Ventricular tachycardia:

    -    Rare in the neonatal period

    -    Mechanism of action: Usually by triggered activity

    -    Can be idiopathic. Other causes include myocarditis, CHD, hypertrophic cardiomyopathy, electrolyte abnormalities

    -    Two types: Idiopathic fascicular VT- Treatment: Verapamil; Right ventricular outflow tract (RVOT) VT – Treatment: Beta-blocker

    -    Unstable VT: DC Cardioversion

Neonatal bradyarrhythmia:

•    Sinus bradycardia:

    -    Benign, resolves in 48 -72 hours

    -    In preterm babies, apnea associated with bradycardia

    -    Other causes: Acidosis, hypoxia, hypoglycemia, and raised ICP

•    Complete AV block:

    -    Heart blocks classified into 3 types: First degree, second degree, and third-degree heart block (more common in neonates)

    -    Third-degree or complete heart block (CHB) presents with bradycardia. There is complete dissociation of atrial and ventricular activity.

    -    EKG: No relationship between the P wave and QRS complex

    -    Maternal connective tissue disorders associated with 90% of the cases

    -    Permanent pacemaker implantation indicated in infants with CHB. In Normal infants with a ventricular rate< 55/min or Congenital heart disease with ventricular rate <70/min

Premature contractions:

•    Premature atrial contractions (PAC):

    -    Detected in 51% of the term newborns

    -    P wave superimposed on T wave; normal QRS duration

    -    Benign; no treatment needed

    -    If persistent, rule out electrolyte abnormalities, hypoxia, hyperthyroidism

•    Premature ventricular contractions (PVC):

    -    Uncommon

    -    Cause: Immaturity of the cardiac conduction tissue

    -    Premature QRS complex with different morphology and no preceding P wave

    -    Isolated PVCs resolves spontaneously

Cardiac Channelopathies:

•    Pathophysiology: Mutation in the genes encoding ion channels

•    Long QT syndrome (LQTS), short QT syndrome (SQTS) are common. 

•    LQTS: 

    -    Diagnosed with QT prolongation with sinus bradycardia or 2:1 AV block

    -    Might progress to polymorphic VT or Torsade's de pointes

    -    Treatment: Beta-blocker. ICD(Implantable cardiac defibrillator) recommended with a family history of SCD

•    SQTS:

    -    QT interval < 330ms

    -    Might progress to Ventricular fibrillation. Treatment: ICD plus antiarrhythmic

Prenatal diagnosis/Perinatal management:

•    Fetal arrhythmias can cause hydrops fetalis and death

•    Analysis in utero possible with M-mode and Doppler echocardiography

•    Fetal Tachycardia: Treated with transplacental Digoxin. Second line: Sotalol, flecainide, and amiodarone

•    Fetal Bradycardia: Treated with beta-agonists and steroids

Message to the clinician:

•    AVRT is the most common tachyarrhythmia in fetus and neonates which require maintenance therapy up to 6-12 months

•    Most common benign arrhythmia is PAC in newborns

•    CHB is the most common bradyarrhythmia that requires post-natal pacemaker implantation

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University of Pittsburgh Medical Center

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