Supraventricular Tachycardia Diagnosis
A 5-year-old boy has sudden onset palpitations and chest discomfort for 45 minutes. He is alert and talking, with a heart rate of 250 beats/min that does not vary with respiration or crying, blood pressure 96/62 mm Hg, capillary refill 2 seconds, and oxygen saturation 99% in room air. The chest is clear with no murmur or gallop. Which of the following is the most appropriate immediate investigation?
- A.Chest radiograph
- B.Twelve lead electrocardiogramCorrect
- C.Transthoracic echocardiogram
- D.Cardiac magnetic resonance imaging
Explanation
A narrow window exists to document the arrhythmia while it is present, so a 12 lead electrocardiogram must be obtained immediately and before any treatment is given, since it defines the rhythm, QRS width, and the presence of preexcitation and guides both acute and long term management. Supraventricular tachycardia in children is defined as a rate above about 220 beats/min in infants and above about 180 beats/min in older children, is strikingly invariant with activity or crying, and typically has a narrow QRS with absent or retrograde P waves. Sinus tachycardia, the main alternative, varies beat to beat with stimulation, rarely exceeds 220 beats/min in a young child, and has identifiable P waves with a normal axis. A chest radiograph adds nothing to rhythm diagnosis in the acute setting, although it may later show cardiomegaly in incessant tachycardia. Echocardiography is useful after conversion to look for structural disease such as Ebstein anomaly or a cardiomyopathy, but obtaining it should not delay rhythm documentation or treatment. Cardiac magnetic resonance imaging has no role in acute arrhythmia management. Because this child is alert with normal perfusion and blood pressure, he is hemodynamically stable and can proceed to vagal maneuvers and then adenosine if needed, with continuous rhythm recording during those attempts. A rhythm strip captured during adenosine administration is diagnostically valuable, since it may unmask atrial flutter or reveal a delta wave once sinus rhythm returns.
Why each option
- A.
- A chest radiograph does not identify the rhythm and delays definitive assessment.
- B.
- Correct. A 12 lead electrocardiogram documents the arrhythmia while present and directs both immediate and long term management.
- C.
- Echocardiography is useful after conversion to look for structural heart disease but is not the immediate investigation.
- D.
- Cardiac magnetic resonance imaging has no role in acute arrhythmia diagnosis.
Reference: AHA Pediatric Advanced Life Support Guidelines, 2020; Nelson Textbook of Pediatrics, 22nd ed., 2024
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