A 58-year-old man with a history of anterior wall myocardial infarction 3 months ago presents to the emergency department with palpitations and lightheadedness. His blood pressure is 85/50 mmHg, heart rate 180 bpm, and respiratory rate 22/min. Physical examination reveals an unresponsive patient. A 12-lead ECG shows a wide complex tachycardia with a rate of 180 bpm; the QRS duration is 160 ms. Cardiac biomarkers are negative. Chest X-ray shows mild cardiomegaly. What is the most appropriate immediate management?

Explanation

## Clinical Scenario Analysis This patient presents with **haemodynamically unstable ventricular tachycardia (VT)** in the context of prior MI with reduced ejection fraction (evidenced by cardiomegaly). The key findings are: - Systolic hypotension (85/50 mmHg) - Altered mental status (unresponsive) - Wide complex tachycardia at 180 bpm - Prior anterior MI (scar substrate for re-entry) ## Management Algorithm for Unstable VT ```mermaid flowchart TD A[Wide Complex Tachycardia]:::outcome --> B{Haemodynamically Stable?}:::decision B -->|No - Hypotension, Altered LOC| C[Synchronized DC Cardioversion]:::action B -->|Yes| D{VT or SVT with aberrancy?}:::decision D -->|Confirmed VT| E[IV Amiodarone or Procainamide]:::action D -->|SVT with aberrancy| F[IV Verapamil or Adenosine]:::action C --> G[Restore Haemodynamics]:::outcome ``` ## Key Point: **Haemodynamic instability (SBP <90 mmHg, altered consciousness, pulmonary oedema, or chest pain) is an absolute indication for immediate synchronized DC cardioversion regardless of the arrhythmia type.** Pharmacological therapy is contraindicated and delays definitive treatment. ## High-Yield: - **Unstable VT/VF → DC cardioversion (100–200 J biphasic or 200–360 J monophasic)** - **Stable VT → Amiodarone 150 mg IV bolus or Procainamide** - **Calcium channel blockers (verapamil) are contraindicated in VT** — they may worsen haemodynamics and increase mortality in ischaemic cardiomyopathy ## Clinical Pearl: In post-MI patients with reduced ejection fraction, VT is often due to re-entry around scar tissue. Immediate electrical therapy restores perfusion; drugs are slower and less reliable in unstable patients. After cardioversion, amiodarone is the preferred agent for secondary prevention. ## Why Synchronized Cardioversion? - Synchronization to the R wave avoids the vulnerable period (T wave) and reduces risk of VF - Immediate restoration of perfusion in haemodynamically compromised patients - Success rate >90% for VT when properly synchronized