A 71-year-old man is admitted to the progressive care unit due to a three-day history of p… — USMLE Step 2 CK

A $71$ -year-old man is admitted to the progressive care unit due to a three-day history of progressively worsening breathlessness, a cough productive of yellowish sputum, and a sensation of a "racing heart." He has a history of essential hypertension and has smoked a pack of cigarettes daily for the past $45$ years. His current medications include amlodipine and a daily multivitamin. On arrival, his temperature is $37.3^\circ\text{C}$ ( $99.1^\circ\text{F}$ ), blood pressure is $132/84\text{ mmHg}$ , heart rate is $128\text{/min}$ and irregularly irregular, and respiratory rate is $26\text{/min}$ . Pulse oximetry shows an oxygen saturation of $89\%$ on ambient air. Physical examination reveals an increased anteroposterior chest diameter and diffuse, high-pitched expiratory wheezing across all lung fields. There is no jugular venous distension, and his lower extremities show no edema. Thyroid function tests drawn on admission reveal a thyroid-stimulating hormone (TSH) of $0.2\ \mu\text{U/mL}$ (normal: $0.4-4.0\ \mu\text{U/mL}$ ) and a free T4 of $0.8\text{ ng/dL}$ (normal: $0.9-1.7\text{ ng/dL}$ ). A 12-lead electrocardiogram demonstrates an irregularly irregular rhythm with narrow QRS complexes and three distinct P-wave morphologies preceding the QRS complexes in lead II. Which of the following is the most appropriate next step in the management of this patient's cardiac finding?

Optimize the underlying pulmonary condition with inhaled bronchodilators and systemic corticosteroidsAnswer
B
Administer intravenous furosemide and initiate noninvasive positive-pressure ventilation
C
Administer broad-spectrum intravenous antibiotics to cover methicillin-resistant Staphylococcus aureus and Pseudomonas aeruginosa
D
Perform an arterial blood gas analysis to apply Winter's formula for guiding bicarbonate administration
E
Administer intravenous levothyroxine to address the primary thyroid dysfunction

Answer

Optimize the underlying pulmonary condition with inhaled bronchodilators and systemic corticosteroids.

The correct answer addresses the root cause of the arrhythmia. This patient's ECG shows multifocal atrial tachycardia (MAT), characterized by an irregularly irregular rhythm with narrow QRS complexes and at least three distinct P-wave morphologies. MAT is most frequently associated with severe pulmonary disease, particularly chronic obstructive pulmonary disease (COPD) exacerbations, due to factors like hypoxemia, right heart stretch, and increased sympathetic tone. The most effective treatment for MAT is not cardioversion or antiarrhythmic medication, but rather aggressive optimization of the underlying pulmonary process with bronchodilators, systemic corticosteroids, and supplemental oxygen therapy.

Step-by-Step Solution

Analyze the clinical presentation and physical exam findings.

The patient has a long smoking history, worsening dyspnea, productive cough, hypoxemia, and diffuse wheezing without signs of volume overload.

These findings strongly indicate an acute exacerbation of chronic obstructive pulmonary disease (COPD).

Interpret the electrocardiogram (ECG) and laboratory findings.

The ECG shows an irregularly irregular narrow-complex tachycardia with three distinct P-wave morphologies, confirming multifocal atrial tachycardia (MAT). The thyroid labs show low TSH and low T4.

Identifying MAT is crucial, as it dictates management. The thyroid labs indicate euthyroid sick syndrome, a non-thyroidal illness common in acute stress, requiring no targeted thyroid therapy.

Determine the most appropriate management for the cardiac arrhythmia.

The treatment for MAT is optimization of the underlying pulmonary disease.

MAT is typically a secondary response to hypoxemia, hypercapnia, or right atrial stretch from lung disease; direct antiarrhythmic therapy is largely ineffective.

Key Concept

Multifocal atrial tachycardia (MAT) is characterized by an irregularly irregular rhythm with at least three distinct P-wave morphologies and is most commonly driven by severe pulmonary disease, such as a COPD exacerbation. Management must focus on aggressively treating the primary respiratory condition rather than administering direct antiarrhythmic therapies.

Estimated Time:1m 30s

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