A 52-year-old woman with a history of palpitations is brought to the emergency department. Her 12-lead ECG shows a regular wide-complex tachycardia at 160 bpm with a rate of 2:1 atrioventricular (AV) block pattern. The QRS duration is 0.16 seconds. Blood pressure is 110/70 mmHg and she is alert. What is the most appropriate immediate next step in management?

Clinical Scenario Analysis

This patient presents with a regular wide-complex tachycardia (WCT) at 160 bpm with 2:1 AV block. The combination of:

...is highly suggestive of atrial flutter with fixed 2:1 AV conduction or atrial tachycardia with AV block, both of which are refractory to adenosine and calcium channel blockers because the arrhythmia originates above the AV node but the AV node is not the rate-limiting structure.

Differential Diagnosis of Wide-Complex Tachycardia

Key Point:

2:1 AV conduction block in a regular WCT indicates the arrhythmia is NOT AV-node-dependent. Adenosine and calcium channel blockers work by blocking AV nodal conduction; they will not terminate arrhythmias where the AV node is merely a passive bystander. In this hemodynamically stable patient, synchronized DC cardioversion is the definitive treatment.

High-Yield Facts

Clinical Pearl:

The 2:1 AV conduction ratio is a clue to atrial flutter. In atrial flutter, the atrial rate is typically 250–350 bpm; the AV node conducts every other impulse (2:1 block) by default, resulting in a ventricular rate of 125–175 bpm. This is a classic ECG pattern and should trigger immediate recognition that adenosine will not work.

Warning:

Adenosine is the first-line drug for all regular WCT — this is a common misconception. Adenosine is first-line only for AV-node-dependent arrhythmias (AVNRT, AVRT). For atrial flutter, atrial tachycardia, and VT, adenosine either has no effect or may transiently increase AV block without terminating the arrhythmia, wasting time.

Verapamil is safe in all WCT — verapamil is contraindicated in VT and can cause hemodynamic collapse. In this case, even if VT were suspected, verapamil would be dangerous.

Management Rationale

Since the patient is hemodynamically stable, sedation is appropriate before cardioversion. Synchronized DC cardioversion at 100–200 J is the gold standard for terminating atrial flutter and other AV-node-independent arrhythmias.

Harrison 21e Ch 296; Braunwald's Heart Disease 12e Ch 36

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