The Case
A 2-month-old boy was seen by his pediatrician earlier in the day for fussiness and poor feeding. At that visit, he was noted to be tachycardic, but the elevated heart rate was attributed to crying and irritability. That evening, his parents brought him to the ED because he continued to breathe rapidly and refused feeds.
Vitals and Exam
| T: 36.8°C/98.2°F | HR: 225 | BP: 72/42 | RR: 60 | SpO₂: 97% on room air |
- Fussy but consolable infant
- Mild subcostal retractions, tachypnea
- Cap refill 3–4 seconds
- Pulses rapid and somewhat weak
- Lungs clear to auscultation, no wheeze or crackles
- No murmurs appreciated
What is the Diagnosis?
Question: What’s going on here? What’s at the top of your differential for a young infant with tachypnea, poor feeding, irritability, and tachycardia?
Click to Reveal the Diagnosis
Diagnosis: Supraventricular Tachycardia (SVT)
This is the most common arrhythmia in children. SVT presents as a narrow-complex tachycardia with little beat-to-beat variability and sudden onset. In infants, rates are usually >220 bpm.
Why It Matters
Infants may compensate for a period of time, but congestive heart failure or shock can develop if SVT isn’t recognized.
The presentation is often nonspecific – tachypnea, poor feeding, irritability – so an ECG and rhythm strip is critical.
First Steps
– Assess cardiorespiratory stability (go through your ABCs)
– Obtain ECG
ECG: Narrow complex tachycardia with little beat-to-beat variability
Management
Stable patients:
Vagal maneuvers (ice bag to face, rectal stimulation in infants, Valsalva in older kids).
IV adenosine (0.1 mg/kg rapid push, max 6 mg) – typically administered via 3-way stopcock and immediately flushed with saline.
Unstable patients:
Synchronized cardioversion (0.5–1 J/kg).
Long-term: May require beta-blockers or other antiarrhythmics; some with WPW may undergo ablation.
What to do if adenosine does not work?
Pearl: You should see a change in rhythm after adenosine, even if transient.
If you do not see any change: Is your IV in place? Is the IV too distal to central circulation (Adenosine half life is <10 seconds)?
If you see a transient change, but then back to SVT: May need to increase your dose (typically to 0.2mg/kg, then 0.3mg/kg), but consider consultation with your Cardiology colleagues for additional guidance.
If you cannot break the patient out of SVT with multiple doses of adenosine: May need other antiarrhythmic medications or synchronized cardioversion (if stable, likely can be done in the ICU with Cardiology guidance).
Resources and Further Education
Single syringe administration of Adenosine?
Should adolescents with palpitations have Holter monitoring done?
Dr. Joshua Belfer, MD, is a Pediatric Emergency Medicine physician at the Children’s Hospital of Philadelphia, and is the Founder and Editor-in-Chief of HipPEMcrates. He can be reached at HipPEMcrates@gmail.com.
