Wide-Complex Tachycardia: Stable, Then Not
Called for a 68-year-old woman with 'fluttering' and lightheadedness that started 40 minutes ago while she was watching television. History of hypertension and an anterior MI in 2019; she takes metoprolol and aspirin. She is pale and diaphoretic but fully alert, oriented, and conversant. The monitor shows a regular wide-complex tachycardia at 176/min with a QRS of 0.16 s; you cannot identify P waves. BP 108/70, SpO2 96% on room air, RR 22, lungs clear, no chest pain, no jugular venous distension, no peripheral edema. Two IVs are in place. You carry adenosine, amiodarone, diltiazem, and a monitor with synchronized cardioversion and pacing.
1. Choose among adenosine, amiodarone, and immediate synchronized cardioversion right now. Justify the choice and state your plan if the first-line drug fails.
Read the worked answer
Treat it as ventricular tachycardia and give amiodarone; do not give diltiazem; keep pads on and cardioversion ready.
Reasoning:
- Regular wide-complex tachycardia is VT until proven otherwise, and the prior anterior MI makes VT far more likely than SVT with aberrancy. Age plus structural heart disease plus a wide regular rhythm is a VT picture.
- She is currently stable: alert, conversant, BP 108/70, clear lungs, no ischemic pain, no signs of heart failure. Stability buys you the option of a drug and time to think.
- Adenosine's role is narrow. It is reasonable only for a stable, regular, monomorphic wide-complex tachycardia when you genuinely suspect SVT with aberrancy, or as a diagnostic maneuver. It is not a treatment for VT.
- Calcium channel blockers are the dangerous choice - diltiazem or verapamil in VT can cause profound hypotension and cardiovascular collapse.
- Immediate cardioversion is not required yet, but it becomes the answer the moment she stops being stable.
Plan: amiodarone 150 mg IV over about 10 minutes with continuous monitoring, 12-lead capture if possible, pads applied. If she deteriorates at any point, abandon the infusion and cardiovert.
2. Ten minutes later she is confused, BP 78/44, RR 26, and the rhythm is unchanged. State your action, your sequence, and the safety points.
Read the worked answer
She is now unstable. Immediate synchronized cardioversion.
Sequence:
- Confirm the rhythm is still organized and has a pulse - if it is now pulseless VT or VF, defibrillate and start CPR instead.
- Apply pads, confirm the monitor shows SYNC markers on each QRS, and select the correct energy (100 J biphasic, or the manufacturer's recommended starting dose).
- Preoxygenate and have suction ready; give sedation (midazolam or etomidate) only if it does not delay the shock. A confused, hypotensive patient can be cardioverted without sedation if you must.
- Shock, then reassess rhythm and pulse immediately; escalate to 200 J, then 300 J, then maximum if needed, and consider a second antiarrhythmic or magnesium per protocol.
Safety points: clear everyone off the stretcher before each shock; make sure sync mode has not dropped out (a common failure - the machine defaults back to unsynchronized after a shock); be ready to manage the post-conversion bradycardia or recurrent VT.
Ask yourself why she is in VT: ischemia (the prior MI), hypoxia, electrolyte abnormality, or drug effect. Fix what you can en route.
3. Suppose instead the monitor shows an irregularly irregular wide-complex tachycardia at about 190 with the same QRS duration. How does your management change?
Read the worked answer
This is a different animal: irregular wide-complex is atrial fibrillation with aberrancy or, critically, pre-excited AF (WPW).
What changes:
- AV nodal blocking drugs become potentially lethal. Adenosine, diltiazem, verapamil, and digoxin can block the node and push conduction down the accessory pathway, producing extremely rapid ventricular rates and degeneration into ventricular fibrillation. Amiodarone is also discouraged in this setting by many protocols.
- If she is unstable: synchronized cardioversion, same as before - shock first, ask questions later.
- If she is stable: this is a rhythm to leave alone on the truck unless your protocol directs otherwise; a procainamide infusion is the classic alternative, but expert consultation or rapid transport is often the better call.
- Look for the tell: delta waves in the sinus beats before or after the run, a very short PR, or a family history of palpitations in a young person. In a 68-year-old with an old MI, AF with aberrancy is statistically more likely - but the safe approach is the same: do not block the node.
Takeaway: rate-based decision making fails here. The regularity and QRS width, not the number on the monitor, drive drug selection.