A 72-year-old man with severe COPD presents to the ICU with acute exacerbation, hypoxia (SpO2 88%), and hypercapnia (pCO2 58 mmHg). Bedside ECG shows an irregularly irregular narrow-complex tachycardia at 130 bpm with at least three distinct P-wave morphologies visible in lead II and varying PR intervals, with a clear isoelectric baseline between P waves. The rhythm shown is marked as **A** in the diagram. Which of the following is the MOST appropriate initial management step for this arrhythmia?

Question

Accepted Answer

A. Correction of hypoxia with supplemental oxygen and treatment of acid-base derangement, plus IV magnesium replacement. ## Why "Correction of hypoxia with supplemental oxygen and treatment of acid-base derangement, plus IV magnesium replacement" is right

The rhythm marked **A** is multifocal atrial tachycardia (MAT), an automatic arrhythmia arising from multiple (≥3) ectopic atrial foci competing with the sinus node. The ECG findings—irregularly irregular rhythm, ≥3 distinct P-wave morphologies, varying PR/PP/RR intervals, and isoelectric baseline between P waves—are pathognomonic for MAT. In COPD patients with hypoxia and hypercapnia, MAT is driven by hypoxia-induced abnormal automaticity, acidosis, and sympathetic activation. The cornerstone of MAT management is **treatment of the underlying disease**: correction of hypoxia (supplemental O₂ targeting SpO₂ 88–92%), correction of acid-base derangement, and replacement of depleted electrolytes (potassium >4 mEq/L, magnesium >2 mg/dL). IV magnesium sulfate (1–2 g) is often directly effective in suppressing MAT automaticity. This patient's hypoxia and hypercapnia are the primary drivers; addressing these will resolve the arrhythmia. (2019 ACC/AHA/HRS SVT Guidelines; Harrison 21e Ch 247; McCord MAT Chest 1998)

## Why each distractor is wrong

- **Immediate DC cardioversion to restore sinus rhythm**: MAT is an automatic arrhythmia, NOT a reentrant arrhythmia. DC cardioversion is ineffective and contraindicated in MAT; it does not terminate automatic rhythms. This approach would be appropriate for atrial fibrillation or atrial flutter (marked **B** or **C**), not MAT.

- **Initiation of IV amiodarone followed by elective cardioversion**: Class I and III antiarrhythmics are generally not helpful in MAT because the rhythm is driven by abnormal automaticity, not reentry. Amiodarone is rarely used and is not first-line. Cardioversion is again inappropriate for an automatic rhythm.

- **Urgent administration of IV digoxin to slow the atrial rate**: Digoxin is contraindicated in MAT and may worsen the arrhythmia, especially in the setting of electrolyte depletion and hypoxia. Digoxin toxicity is itself a known precipitant of MAT. Rate control with digoxin is not appropriate.

**High-Yield:** MAT in COPD = treat the lung disease and electrolytes, NOT the rhythm itself; cardioversion does not work for automatic arrhythmias.

[cite: 2019 ACC/AHA/HRS SVT Guidelines; Harrison 21e Ch 247; McCord MAT Chest 1998]

Answer

B. Urgent administration of IV digoxin to slow the atrial rate

Answer

C. Immediate DC cardioversion to restore sinus rhythm

Answer

D. Initiation of IV amiodarone followed by elective cardioversion

Explanation

Why "Correction of hypoxia with supplemental oxygen and treatment of acid-base derangement, plus IV magnesium replacement" is right

Why each distractor is wrong

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