A 50-year-old man is brought to the emergency department due to chest pain and lightheadedness for the past hour. He was clearing away snow when he suddenly felt substernal chest pressure accompanied by cold sweats. The pain has been constant, radiates to the left jaw, and is not relieved by rest or the nitroglycerin spray he received in the ambulance. The patient has a history of well-controlled hypertension. He smokes occasionally, especially on weekends, but does not use alcohol. His father had a myocardial infarction at age 60. On examination, the patient appears to be in mild distress. The extremities are cold. Temperature is 36.1 C (97 F), blood pressure is 84/52 mm Hg, pulse is 34/min, and respirations are 16/min. Oxygen saturation is 94% on 4 L/min nasal cannula oxygen. Lung auscultation reveals crackles at both lung bases. There are no heart murmurs. The abdomen is soft and nontender. ECG shows sinus bradycardia with a 3-mm ST-segment elevation in leads II, III, and AVF. Which of the following is most appropriate as part of initial management for this patient?

Question

A 50-year-old man is brought to the emergency department due to chest pain and lightheadedness for the past hour.  He was clearing away snow when he suddenly felt substernal chest pressure accompanied by cold sweats.  The pain has been constant, radiates to the left jaw, and is not relieved by rest or the nitroglycerin spray he received in the ambulance.  The patient has a history of well-controlled hypertension.  He smokes occasionally, especially on weekends, but does not use alcohol.  His father had a myocardial infarction at age 60.  On examination, the patient appears to be in mild distress.  The extremities are cold.  Temperature is 36.1 C (97 F), blood pressure is 84/52 mm Hg, pulse is 34/min, and respirations are 16/min.  Oxygen saturation is 94% on 4 L/min nasal cannula oxygen.  Lung auscultation reveals crackles at both lung bases.  There are no heart murmurs.  The abdomen is soft and nontender.  ECG shows sinus bradycardia with a 3-mm ST-segment elevation in leads II, III, and AVF.  Which of the following is most appropriate as part of initial management for this patient?

Quizplus · Accepted Answer

Explanation: This patient has developed sinus bradycardia as a complication of acute inferior wall myocardial infarction (MI). Inferior wall MI typically results from blockage of the right coronary artery and may involve only the right ventricle or both the left and right ventricles. The sinoatrial node is supplied by the right coronary artery in 60% of patients; sinus bradycardia commonly occurs due to ischemia of the sinoatrial node and right ventricular wall triggering an increase in vagal tone. Sinus bradycardia after an inferior wall MI is usually transient and self-limited; however, severe bradycardia can occur and lead to cardiogenic shock (eg, hypotension, cold extremities, pulmonary edema). Anticholinergic therapy with intravenous atropine is the initial treatment of choice for patients with hemodynamically significant bradycardia due to inferior wall MI, and typically results in increased cardiac output and improvement in symptoms. (Choice B) Dobutamine is a beta-1 agonist that treats cardiogenic shock primarily through an increase in left ventricular contractility. This patient's cardiogenic shock is mostly due to inadequate heart rate rather than inadequate contractility, and is better addressed with atropine. (Choice C) Epinephrine is sometimes used for symptomatic bradycardia that does not respond to atropine; however, due to beta-1 and alpha-1 stimulation leading to a large increase in myocardial oxygen demand, epinephrine is typically contraindicated in patients with MI. Temporary cardiac pacing is the treatment of choice in patients with MI and sinus bradycardia that does not respond to atropine. (Choice D) Although patients with right ventricular MI are typically preload-dependent with clear lungs and should often be initially managed as if they are hypovolemic, this patient's severe bradycardia has led to inadequate left ventricular cardiac output causing pulmonary edema (evidenced by bibasilar crackles) and cardiogenic shock. The administration of normal saline without increasing heart rate will cause worsening pulmonary edema. (Choice E) Nitroglycerin infusion causes decreased preload due to dilation of venous capacitance vessels, and can be used to relieve pulmonary edema in some scenarios (eg, hypertensive emergency). However, it is contraindicated in patients with hypotension and/or preload-dependent right ventricular MI. Educational objective: Acute inferior wall myocardial infarction often causes sinus bradycardia due to an increase in vagal tone triggered by sinoatrial node and right ventricular wall ischemia. Intravenous atropine is the initial treatment of choice in patients with hemodynamically significant bradycardia (eg, pulmonary edema, hypotension) due to inferior wall myocardial infarction. References: Sinus bradycardia as a predictor of right coronary artery occlusion in patients with inferior myocardial infarction. (http://www.ncbi.nlm.nih.gov/pubmed/10077404)

A 50-Year-Old Man Is Brought to the Emergency Department Due