PALS Tachycardia With a Pulse 5 — Questions and Answers
Question 1: A 9-year-old with SVT receives adenosine via a peripheral IV in the antecubital fossa. The rhythm does not convert. What is the most likely reason for failure?
- Adenosine was not followed by a rapid saline flush (Correct answer)
- The dose was too high for the patient's weight
- The IV was placed too proximally
- Adenosine is ineffective in children over 8 years
Correct answer: Adenosine was not followed by a rapid saline flush
Failure to immediately flush adenosine with normal saline allows the drug to be inactivated before reaching the central circulation due to its 10-second half-life.
Question 2: In pediatric tachycardia assessment, what does the PALS algorithm define as the primary distinction between 'stable' and 'unstable' tachycardia?
- Presence or absence of signs of cardiopulmonary compromise (Correct answer)
- Heart rate above or below 200 bpm
- Narrow versus wide QRS complex duration
- Patient's age and weight
Correct answer: Presence or absence of signs of cardiopulmonary compromise
PALS classifies tachycardia as unstable when there are signs of cardiopulmonary compromise such as poor perfusion, hypotension, or altered mental status.
Question 3: A 1-year-old infant is in SVT with a rate of 260 bpm and is feeding poorly with mottled skin. There is no IV or IO access. What is the most appropriate immediate step?
- Apply ice bag to the face briefly to stimulate the diving reflex (Correct answer)
- Attempt defibrillation while IV access is established
- Administer intranasal midazolam for sedation
- Wait for IV access before any intervention
Correct answer: Apply ice bag to the face briefly to stimulate the diving reflex
Ice application to the infant's face stimulates the diving reflex as a vagal maneuver and can be performed immediately without IV access.
Question 4: Which statement correctly describes ventricular tachycardia (VT) with a pulse in a pediatric patient compared to SVT with aberrancy?
- VT more commonly shows AV dissociation and fusion beats on ECG (Correct answer)
- SVT with aberrancy always has a wider QRS than VT
- VT is more common than SVT in infants under 1 year
- VT always terminates spontaneously without intervention
Correct answer: VT more commonly shows AV dissociation and fusion beats on ECG
AV dissociation (P-waves unrelated to QRS complexes) and fusion beats are classic ECG findings that favor VT over SVT with aberrancy.
Question 5: For a child with SVT who has IV access established, at what site should adenosine ideally be injected for fastest effect?
- A large proximal vein such as the antecubital or central line (Correct answer)
- A small distal hand vein
- Any peripheral IV with gravity drip running
- Directly into the endotracheal tube
Correct answer: A large proximal vein such as the antecubital or central line
Adenosine should be injected into a large proximal vein (or central line) to minimize transit time to the heart given its ultra-short half-life.
Question 6: Which of the following best describes the mechanism by which adenosine terminates SVT?
- It transiently blocks AV nodal conduction, interrupting the re-entrant circuit (Correct answer)
- It directly cardioverts the atria to sinus rhythm
- It suppresses ventricular ectopy by blocking sodium channels
- It increases vagal tone through catecholamine release
Correct answer: It transiently blocks AV nodal conduction, interrupting the re-entrant circuit
Adenosine transiently blocks the AV node, interrupting the re-entry circuit that sustains SVT and allowing the sinus node to re-establish control.
Question 7: A child with tachycardia has a QRS duration of 0.08 seconds. How should this QRS be classified and what does it suggest?
- Narrow QRS; suggests a supraventricular origin of the tachycardia (Correct answer)
- Wide QRS; suggests ventricular tachycardia
- Normal QRS; rules out any arrhythmia
- Borderline QRS; requires immediate defibrillation
Correct answer: Narrow QRS; suggests a supraventricular origin of the tachycardia
A QRS duration less than 0.09 seconds is considered narrow in children, indicating conduction through the normal His-Purkinje system and suggesting a supraventricular origin.
PALS Tachycardia With a Pulse 5
A 9-year-old with SVT receives adenosine via a peripheral IV in the antecubital fossa.
The rhythm does not convert.
What is the most likely reason for failure?