A 58-year-old man with a history of anterior wall myocardial infarction 6 months ago presents to the emergency department with palpitations and lightheadedness. His blood pressure is 88/56 mmHg, heart rate 140 bpm. ECG shows a wide complex tachycardia (QRS duration 160 ms) with AV dissociation and capture beats visible. Echocardiography reveals an ejection fraction of 35%. What is the most appropriate immediate management?

Explanation

## Diagnosis: Ventricular Tachycardia (VT) with Haemodynamic Instability ### Clinical Recognition **Key Point:** This patient has a wide complex tachycardia (QRS 160 ms) with AV dissociation and capture beats — findings **pathognomonic for VT**. The blood pressure of 88/56 mmHg confirms **haemodynamic instability** (SBP < 90 mmHg). History of anterior MI with EF 35% further supports VT as the diagnosis. ### Why Immediate Unsynchronized Defibrillation? **High-Yield:** Per ACLS guidelines (and Harrison's Principles of Internal Medicine, 21e, Ch. 226), the management of **haemodynamically unstable VT** is: > **Immediate electrical cardioversion/defibrillation — do NOT delay for antiarrhythmic drugs.** - When a patient with VT is **haemodynamically unstable** (hypotension, altered consciousness, signs of shock), the first-line treatment is **immediate electrical therapy**, not pharmacological therapy. - In pulseless VT or VT with severe haemodynamic compromise, **unsynchronized defibrillation at 200 J (biphasic)** is appropriate because synchronization may fail or delay treatment in a rapidly deteriorating patient. - Amiodarone is appropriate for **stable VT** or as an adjunct *after* cardioversion to prevent recurrence — it is NOT the first step when the patient is already in shock. **Clinical Pearl:** The distinction is critical: | Situation | First-line Treatment | |---|---| | Stable VT (SBP > 90) | IV Amiodarone or Procainamide | | Unstable VT (SBP < 90, conscious) | Synchronized cardioversion | | Pulseless VT / severe instability | Unsynchronized defibrillation | This patient's SBP of 88 mmHg with lightheadedness places him in the **unstable** category requiring **immediate electrical therapy**. Delaying with amiodarone risks further haemodynamic deterioration and cardiac arrest. ### Why Not Option C (Amiodarone first)? **Warning:** While amiodarone is a valuable antiarrhythmic, administering it *before* electrical cardioversion in an unstable patient: - Delays definitive treatment - Amiodarone has a slow onset of action (minutes to hours for full effect) - Its negative inotropic effects may worsen hypotension - ACLS guidelines explicitly state: **do not delay cardioversion to administer antiarrhythmics** in unstable VT ### Why Not Verapamil (Option D)? Verapamil is **absolutely contraindicated** in VT — it is a negative inotrope, will worsen hypotension, and does not reliably terminate VT. It is indicated for SVT only. ### Why Not Observation (Option A)? Observation is never appropriate in haemodynamically unstable VT. Immediate intervention is mandatory. **Mnemonic:** **SHOCK = Stabilize with electricity first** — in unstable VT, electricity (defibrillation/cardioversion) is always the priority over pharmacology. [cite: Harrison 21e Ch. 226; AHA/ACLS Guidelines 2020]