Wide Complex at 210 in a Collapsing Athlete
A 13-year-old (50 kg) collapses during a basketball game, then stands up pale and dizzy. The monitor shows a regular wide-complex tachycardia at 210/min with a QRS of 0.14 s, blood pressure 82/45 mmHg, SpO2 96%, and capillary refill of 3 seconds. He is awake but confused about where he is and denies any prior episodes, medications, or drug use. A 12-lead ECG is being set up, and one team member has drawn up adenosine while another calls for the defibrillator. The child remains conscious with a palpable radial pulse.
1. Is this child stable or unstable, and does he need electricity now? Justify your answer over the alternative of waiting for the 12-lead ECG.
Read the worked answer
Unstable - and yes, he needs electricity now.
Unstable means signs of inadequate perfusion, not a specific rhythm:
- Hypotension (82/45) for a 13-year-old
- Altered mental status (confused about place)
- Pallor and prolonged capillary refill (3 s)
- Wide-complex tachycardia at 210 with a palpable pulse
In an unstable patient with a tachyarrhythmia and a pulse, synchronized cardioversion is the treatment regardless of whether the rhythm is ventricular tachycardia or SVT with aberrancy - you do not need to make that distinction before treating. Waiting for a 12-lead or a diagnostic drug risks decompensation to pulseless arrest.
Adenosine is for stable narrow-complex SVT (and may be used diagnostically in stable, regular, monomorphic wide-complex tachycardia). It is not the first move in an unstable child. If he loses his pulse during preparation, switch immediately to unsynchronized defibrillation.
2. State your first energy dose and sedation approach, then what you do if the first shock fails and if he becomes pulseless.
Read the worked answer
First synchronized cardioversion: 0.5–1 J/kg = 25–50 J for this 50 kg child (start at 0.5–1 J/kg; many would choose 50 J).
Sedation: if he is conscious and time permits, give procedural sedation (e.g., ketamine 1–2 mg/kg IV) with airway equipment and suction ready. If he is deteriorating toward pulselessness, shock without waiting for sedation.
If the first shock fails:
- Escalate to 2 J/kg = 100 J
- Consider amiodarone 5 mg/kg IV (250 mg, max 300 mg) over 20–60 minutes, or lidocaine
- Correct electrolytes (potassium, magnesium), review for long QT or channelopathy, and screen for structural causes
If he becomes pulseless (VF/pulseless VT):
- Defibrillate 2 J/kg (100 J), then 4 J/kg (200 J), then ≥4 J/kg on subsequent shocks (max 10 J/kg or the adult dose)
- Start CPR immediately after each shock and give epinephrine 0.01 mg/kg IV/IO every 3–5 minutes
The reasoning: synchronized cardioversion should interrupt an organized ventricular rhythm; a failed first shock means under-dosing or a refractory substrate, both of which call for escalation rather than repetition at the same energy.
3. Suppose instead the rhythm were narrow-complex SVT at 210 with the same blood pressure. How would your first step change - and what if the blood pressure were normal?
Read the worked answer
With the same hypotension and altered mentation, nothing changes: synchronized cardioversion 0.5–1 J/kg. QRS width does not determine the need for electricity; perfusion does.
If he were hemodynamically stable (normal BP, alert, good perfusion), the sequence would be:
- Vagal maneuvers (modified Valsalva, ice to the face in a younger child)
- Adenosine 0.1 mg/kg rapid IV push (max 6 mg), followed by 0.2 mg/kg (max 12 mg) if needed - give it as close to the heart as possible with a rapid saline flush
- If adenosine fails or SVT recurs: expert consultation for a beta-blocker, amiodarone, or synchronized cardioversion
The decision tree being tested: stability determines electricity; rhythm determines the drug. An unstable patient never gets a diagnostic adenosine trial, and a stable patient rarely needs immediate cardioversion.