A 72-year-old male is rushed to the emergency unit because of rapid heartbeat and feeling unwell for the past hour. He denies chest discomfort and has not fainted. He has no known cardiac history, but mentions having severe diarrhoea for several days, which he attributes to “something he ate.”
His ECG shows a regular wide-complex tachycardia at 240 beats/min, with a QRS duration of 150 ms. He is alert, maintains good blood pressure, and apart from the tachycardia, the physical exam is unremarkable.
A blood test reveals:
Potassium: 2.5 mmol/L (low)
Which medication should NOT be given in this situation?
A. Amiodarone
B. Potassium-containing IV fluids
C. Lignocaine
D. Procainamide
E. Verapamil ✔️
Detailed Explanation
This man’s ECG shows a regular wide-complex tachycardia. When the heart beats extremely fast with wide QRS complexes (≥120 ms), the most likely diagnosis is ventricular tachycardia (VT)—especially in an older adult with electrolyte imbalance.
Why is VT likely here?
- Rate extremely fast (240/min)
- Wide QRS (150 ms)
- Occurs in setting of severe hypokalaemia
- Older patient
Although supraventricular tachycardia (SVT) with aberrancy can mimic VT, in emergency medicine, all wide-complex tachycardias are treated as VT until proven otherwise. Treating VT as SVT can be fatal.
Why avoid Verapamil?
Verapamil is a calcium-channel blocker, used for SVT, NOT VT.
If verapamil is given in VT:
- profound hypotension may occur
- may deteriorate into ventricular fibrillation
- may cause cardiac arrest
Therefore, verapamil is absolutely contraindicated in VT.
Which drugs are appropriate?
- Amiodarone → first-line for stable VT
- Lignocaine (lidocaine) → alternative antiarrhythmic
- Procainamide → another option for stable VT
- IV fluids with potassium → needed to correct severe hypokalaemia, a trigger for VT
Why the potassium matters?
Hypokalaemia increases:
- risk of ventricular arrhythmias
- QT prolongation
- ectopic electrical activity
Correcting potassium helps stabilise the cardiac membrane.
Cheat Sheet (Exam-Ready)
Wide-complex tachycardia → assume VT unless proven otherwise
- Most common cause: ventricular tachycardia
- Treat as VT in emergencies
- Hypokalaemia is a known trigger
VT characteristics
- Regular rhythm
- Wide QRS ≥120 ms
- Rate typically 150–250 bpm
Management of stable VT
- Amiodarone
- Procainamide
- Lidocaine
- Correct potassium/magnesium
Drugs contraindicated
❌ Verapamil (never use in VT)
Causes collapse → VF → cardiac arrest
Unstable VT
→ Immediate synchronised DC cardioversion
Underlying causes to check
- Electrolyte abnormalities (K+, Mg2+)
- Ischaemia/MI
- Drug toxicity
- Structural heart disease
Flashcards (20 cards)
1.
Q: What is the default assumption for any wide-complex tachycardia?
A: Ventricular tachycardia.
2.
Q: What ECG feature strongly suggests VT?
A: QRS ≥120 ms and very fast rate.
3.
Q: What electrolyte abnormality commonly triggers VT?
A: Hypokalaemia.
4.
Q: Potassium level that increases arrhythmia risk significantly?
A: <3.0 mmol/L.
5.
Q: First-line antiarrhythmic for stable VT?
A: Amiodarone.
6.
Q: Alternative drugs used in stable VT?
A: Lidocaine and procainamide.
7.
Q: What drug must be avoided in VT?
A: Verapamil.
8.
Q: Why avoid verapamil in VT?
A: Causes severe hypotension/VF.
9.
Q: When is verapamil appropriate?
A: For supraventricular tachycardias.
10.
Q: What is the treatment for unstable VT?
A: Synchronized cardioversion.
11.
Q: Key symptom of unstable VT?
A: Hypotension, chest pain, syncope.
12.
Q: In VT, is it safe to delay treatment to clarify diagnosis?
A: No—treat immediately.
13.
Q: Common mimic of VT?
A: SVT with aberrancy.
14.
Q: Best approach when unsure SVT vs VT?
A: Treat as VT.
15.
Q: What ion replacement stabilises the myocardium?
A: Potassium.
16.
Q: What arrhythmia does diarrhoea predispose to?
A: VT (due to hypokalaemia).
17.
Q: Preferred line for amiodarone infusion?
A: Central venous line.
18.
Q: Lidocaine caution?
A: Avoid in severe LV failure.
19.
Q: Long-term prevention for recurrent VT?
A: ICD implantation.
20.
Q: Diagnostic criteria helping differentiate VT from SVT?
A: Brugada criteria.
MCQs (with answers & explanations)
MCQ 1
A 70-year-old man presents with a regular, wide-complex tachycardia. Potassium is 2.7 mmol/L. Which drug should NOT be used?
A. Amiodarone
B. Lidocaine
C. Verapamil ✔️
D. Procainamide
E. IV potassium
Explanation: Verapamil is contraindicated in VT.
MCQ 2
What is the most likely diagnosis in a 240/min wide-complex tachycardia in an elderly patient with hypokalaemia?
A. Atrial flutter
B. Sinus tachycardia
C. VT ✔️
D. SVT with aberrancy
E. AF with RVR
MCQ 3
Which electrolyte abnormality increases risk of ventricular arrhythmias?
A. Hypercalcaemia
B. Hypokalaemia ✔️
C. Hyponatraemia
D. Hypermagnesaemia
E. Hyperchloraemia
MCQ 4
A patient with stable VT is haemodynamically normal. Appropriate first-line therapy?
A. Verapamil
B. DC shock
C. Amiodarone ✔️
D. Adenosine
E. Atropine
MCQ 5
What is the definitive treatment for recurrent, life-threatening VT?
A. Verapamil
B. Beta-blockers only
C. ICD implantation ✔️
D. Digoxin
E. Adenosine
Summary
Wide-complex tachycardia should almost always be considered ventricular tachycardia (VT) until proven otherwise, especially in older patients or those with electrolyte abnormalities. VT typically presents as a rapid, regular rhythm with a wide QRS complex. Hypokalaemia is a major risk factor for ventricular arrhythmias because it destabilises cardiac electrical conduction. In stable VT, antiarrhythmic drugs such as amiodarone, procainamide, or lidocaine are appropriate. Severe hypokalaemia must be corrected urgently, as it is a reversible cause of VT. Verapamil must never be used in VT, as it can induce severe hypotension, ventricular fibrillation, or cardiac arrest. Verapamil is reserved for supraventricular tachycardias, not ventricular arrhythmias. When the diagnosis is uncertain between SVT and VT, it is safer to treat as VT. If the patient shows signs of instability—hypotension, chest pain, syncope—immediate synchronised cardioversion is required. Long-term management may include electrophysiology studies or ICD implantation for prevention of recurrent VT. Evaluation should always include assessment for triggers such as electrolyte imbalance, myocardial ischaemia, or drug toxicity. The overall principle: wide = bad; treat as VT and never give verapamil.