A 68-year-old male with severe COPD presents to the emergency department with acute dyspnea and palpitations. His ECG shows an irregular tachycardia with a ventricular rate of 115 bpm. The rhythm strip reveals the pattern marked **B** in the diagram — multiple distinct P-wave morphologies with an isoelectric baseline between P waves and varying P-P, PR, and R-R intervals. Serum potassium is 3.2 mEq/L and magnesium is 1.6 mg/dL. Which of the following is the most appropriate INITIAL management step for this arrhythmia?

Why IV magnesium sulfate and potassium repletion is correct

The rhythm marked B is multifocal atrial tachycardia (MAT), defined by ≥3 distinct P-wave morphologies with isoelectric baseline and varying intervals. MAT reflects enhanced automaticity from multiple ectopic atrial foci and is most commonly associated with COPD exacerbations (60–85% of cases). The pathophysiology is driven by electrolyte disturbances, particularly hypokalemia and hypomagnesemia, which lower the threshold for ectopic automaticity. Management of MAT is primarily directed at treating the underlying condition. IV magnesium sulfate (1–2 g over 15–60 minutes) is often effective even with normal serum levels, and potassium repletion (target K+ >4 mEq/L) addresses a key precipitant. Concurrent aggressive COPD management (bronchodilators, corticosteroids, oxygen therapy to correct hypoxemia) addresses the root cause. This approach aligns with Harrison's and Braunwald's emphasis that MAT is a marker of disease severity, not a primary cardiac problem requiring antiarrhythmic therapy.

Why each distractor is wrong

Harrison's Principles of Internal Medicine, 21e; Braunwald's Heart Disease, 12e; Marriott's Practical Electrocardiography, 12e