A 72-year-old man comes to the emergency department due to progressive shortness of breath and cough productive of yellowish sputum. The patient says, "I have been feeling breathless for the past several months while mowing the lawn or walking around the house, but it has been worse over the last 3 days." He has had no chest pain or leg swelling but notes that his heart "has been racing." The patient has a history of hypertension, peptic ulcer disease, and osteoarthritis. He was hospitalized for pneumonia a year ago and required intravenous antibiotics. Six months ago, the patient underwent a cardiac stress test for chest discomfort, which was unremarkable. The patient has smoked a pack of cigarettes daily for 45 years. Blood pressure is 160/90 mm Hg, pulse is 148/min, and respirations are 26/min. He is speaking in partial sentences and using accessory muscles of respiration but is alert and cooperative. There is no jugular venous distension or heart murmurs, rub, or gallops, but the heart sounds are irregular. Lung auscultation reveals bilateral rhonchi and expiratory wheezes. Arterial blood gases while breathing 2 L of oxygen via nasal cannula reveal PO₂ of 66 mm Hg, PCO₂ of 52 mm Hg, and pH 7.33. ECG shows narrow QRS complexes with distinct P waves of different morphologies and variable PR segments and R-R intervals. Chest x-ray reveals no pulmonary infiltrates or consolidation. Inhaled bronchodilators and systemic glucocorticoids are administered. The patient's dyspnea has improved after initial treatment in the emergency department, but he continues to have palpitations. Pulse is 125/min and irregular. Blood pressure is 140/88 mm Hg and respirations are 16/min. Oxygen saturation is 92% on 2 L oxygen via nasal cannula. ECG findings are unchanged from the time of admission. Laboratory results are as follows: Which of the following is the most appropriate next step in management of this patient?

Question

Quizplus · Accepted Answer

Explanation: This patient has persistent multifocal atrial tachycardia (MAT) following initial treatment and improvement of his exacerbation of chronic obstructive pulmonary disease. Electrolyte disturbances (eg, hypokalemia, hypomagnesemia) are a common cause of MAT; therefore, laboratory results show another underlying disturbance that should be addressed. The next step in managing this patient's MAT should be adequate potassium replacement; further history should be collected as well to elucidate the cause of his hypokalemia (eg, diarrhea, diuretic use). Preferably, serum potassium should be replaced to a level of 4.0 mEq/L, and serum magnesium should be maintained at (or replaced to) a level of 2.0 mEq/L. Repletion of depleted electrolytes will often lead to conversion to sinus rhythm in patients with MAT. (Choice A) This patient's hyponatremia is likely due to poor oral intake and intravascular volume depletion in the setting of a recent upper respiratory illness. Gentle rehydration will likely correct the hyponatremia. Hypertonic saline is reserved for severe, symptomatic hyponatremia (eg, seizures, profound confusion). (Choices B and C) Intravenous beta blockers (eg, esmolol) and nondihydropyridine calcium channel blockers (eg, verapamil) slow conduction of the atrioventricular node and can be used to control the rapid ventricular rate of MAT. However, these drugs should not be initiated until the potentially correctable causes of MAT have been adequately addressed. (Choice E) Anticoagulation (eg, unfractionated heparin) is indicated in patients with atrial flutter or atrial fibrillation to lower the risk of systemic thromboembolism. However, patients with MAT do not have an increased risk of left atrial thrombus formation, and anticoagulation is not indicated. Educational objective: The initial management of multifocal atrial tachycardia (MAT) is directed toward correction of underlying disturbances (eg, exacerbation of pulmonary disease, hypokalemia). Calcium channel blockers or beta blockers can be used for rate control in patients for whom MAT persists despite correction of potential underlying causes. References: 2015 ACC/AHA/HRS guideline for the management of adult patients with supraventricular tachycardia: a report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines and the Heart Rhythm Society. (http://www.ncbi.nlm.nih.gov/pubmed/26399663) Magnesium and potassium therapy in multifocal atrial tachycardia. (http://www.ncbi.nlm.nih.gov/pubmed/4050650)

A 72-Year-Old Man Comes to the Emergency Department Due to Progressive