A 67-year-old woman with known atrial fibrillation on warfarin presents with acute onset dyspnea and palpitations. Her heart rate is 156/min and blood pressure is 88/54 mmHg. A 12-lead ECG shows a rapid, irregularly irregular rhythm with no discernible P waves and a QRS duration of 0.08 seconds. The QT interval cannot be reliably measured due to the rapid rate. What is the most appropriate immediate next step in management?

Explanation

## Acute Management of Haemodynamically Unstable Atrial Fibrillation with Rapid Ventricular Response **Key Point:** A patient with rapid atrial fibrillation and haemodynamic instability (hypotension, dyspnea) requires immediate electrical cardioversion, not pharmacologic rate control. ### Clinical Recognition **High-Yield:** Haemodynamic instability in the setting of a tachyarrhythmia is an absolute indication for synchronized direct current (DC) cardioversion, regardless of the underlying rhythm diagnosis. | Finding | Significance | |---------|-------------| | HR 156/min | Rapid ventricular response | | BP 88/54 mmHg | Hypotension (cardiogenic shock) | | Dyspnea | Pulmonary congestion / reduced cardiac output | | Irregularly irregular rhythm | Atrial fibrillation | | Narrow QRS (0.08 s) | Supraventricular origin | ### Why DC Cardioversion Is Indicated This patient meets criteria for emergency cardioversion: 1. **Haemodynamic instability** — systolic BP <90 mmHg, acute dyspnea 2. **Rapid ventricular response** — HR >150/min 3. **Symptomatic** — palpitations, respiratory distress **Mnemonic: UNSTABLE** — **U**rge for cardioversion if **N**ot stable, **S**evere symptoms, **T**achycardia >150, **A**cute onset, **B**lood pressure low, **L**ung congestion, **E**mergency presentation. ### Procedure ```mermaid flowchart TD A[Rapid AF with haemodynamic instability]:::outcome --> B{Conscious?}:::decision B -->|Yes| C[Sedate with IV midazolam/propofol]:::action B -->|No| D[Proceed to cardioversion] C --> E[Synchronized DC cardioversion 100-200 J]:::action D --> E E --> F{Sinus rhythm restored?}:::decision F -->|Yes| G[Continuous monitoring, anticoagulation]:::action F -->|No| H[Repeat at higher energy 200-360 J]:::action ``` **Clinical Pearl:** "Synchronized" cardioversion is essential to avoid delivery of energy during the vulnerable period (T wave), which could precipitate ventricular fibrillation. Unsynchronized defibrillation is reserved for VF only. --- ### Why Other Options Are Inappropriate **Measuring QTc after rate control:** QT interval measurement is a diagnostic consideration in stable patients; it is irrelevant in acute haemodynamic instability and delays life-saving intervention. **Intravenous digoxin:** Digoxin has a slow onset (30–60 minutes) and is contraindicated in haemodynamically unstable patients. It is used for rate control in stable AF, not emergency situations. **Chest X-ray and troponin:** These investigations are appropriate for risk stratification but must not delay cardioversion in a haemodynamically unstable patient. They can be performed post-cardioversion. [cite:Harrison 21e Ch 226]