A 58-year-old man with a history of anterior wall myocardial infarction 2 years ago presents to the emergency department with palpitations and lightheadedness. His blood pressure is 110/70 mmHg and he is alert. ECG shows a regular tachycardia at 180 bpm. The structure marked **A** in the diagram—a wide QRS complex (≥120 ms) with regular rhythm—is observed. On closer inspection, independent P waves are visible at a slower rate than the QRS complexes, and occasional narrow QRS complexes are seen interspersed among the wide beats. Given these findings, which of the following is the most appropriate immediate management?

Explanation

## Why Intravenous amiodarone 150 mg bolus over 10 minutes is right The presence of the wide QRS complex marked **A** (≥120 ms, regular rhythm), combined with independent P waves (AV dissociation) and occasional narrow QRS complexes (capture/fusion beats), is pathognomonic for monomorphic ventricular tachycardia (MMVT). The patient's history of prior MI with a scar-related reentrant substrate, hemodynamic stability (BP 110/70, alert), and regular monomorphic rhythm confirm MMVT. Per the 2017 AHA/ACC/HRS Guideline and Harrison's Chapter 249, hemodynamically stable MMVT is managed with pharmacologic conversion; amiodarone 150 mg IV bolus over 10 minutes is the first-line agent per ACLS protocols, with procainamide as an alternative. The presence of pathognomonic features (AV dissociation, capture/fusion beats) definitively establishes VT, making this diagnosis certain. ## Why each distractor is wrong - **Intravenous verapamil 5 mg bolus**: Verapamil and diltiazem are contraindicated in wide-complex tachycardia of uncertain origin, and especially in confirmed VT. These calcium channel blockers can cause catastrophic hemodynamic decompensation and accelerate the arrhythmia if VT is present. Although the patient is currently stable, verapamil is not appropriate for MMVT. - **Observation with continuous monitoring, as this is benign**: While some idiopathic VTs (e.g., RVOT or fascicular VT) originating from structurally normal hearts may be tolerated, this patient has a prior MI with scar-related substrate and is experiencing symptomatic tachycardia (palpitations, lightheadedness). Sustained MMVT in the post-MI setting is life-threatening and requires active intervention, not observation alone. - **Synchronized DC cardioversion at 100–200 J**: Cardioversion is reserved for hemodynamically unstable VT (hypotension, altered mental status, ischemia, or heart failure). This patient is hemodynamically stable (BP 110/70, alert), making pharmacologic conversion the preferred first-line approach. Cardioversion would be appropriate if hemodynamic deterioration occurs. **High-Yield:** AV dissociation and capture/fusion beats are pathognomonic for VT; their presence in a wide-complex tachycardia confirms the diagnosis and mandates VT-specific therapy. In stable MMVT, amiodarone is first-line; verapamil is contraindicated and can be catastrophic. [cite: Harrison Principles of Internal Medicine 21e Ch 249; 2017 AHA/ACC/HRS Guideline for Management of Ventricular Arrhythmias]