A 55-year-old man comes to the emergency department due to an hour of intense substernal chest burning accompanied by sweating. He has a history of obesity and diet-controlled type 2 diabetes mellitus. On initial evaluation, blood pressure is 110/70 mm Hg and pulse is 60/min and regular. Oxygen saturation is 98% on room air. The patient is comfortable lying flat and no heart murmurs are heard. Lungs are clear on auscultation. Immediate ECG shows normal sinus rhythm with a 2-mm ST-segment elevation in leads II, III, and aVF. Aspirin and morphine are administered. As the patient is about to be transported to the catheterization lab for urgent percutaneous coronary intervention, he develops dizziness and the telemetry monitor shows sinus bradycardia at 40/min. The patient appears pale and diaphoretic and peripheral pulses are faint. Blood pressure is 70/40 mm Hg. Which of the following is the best immediate step for managing this patient's condition?

Question

A 55-year-old man comes to the emergency department due to an hour of intense substernal chest burning accompanied by sweating.  He has a history of obesity and diet-controlled type 2 diabetes mellitus.  On initial evaluation, blood pressure is 110/70 mm Hg and pulse is 60/min and regular.  Oxygen saturation is 98% on room air.  The patient is comfortable lying flat and no heart murmurs are heard.  Lungs are clear on auscultation.  Immediate ECG shows normal sinus rhythm with a 2-mm ST-segment elevation in leads II, III, and aVF.  Aspirin and morphine are administered.  As the patient is about to be transported to the catheterization lab for urgent percutaneous coronary intervention, he develops dizziness and the telemetry monitor shows sinus bradycardia at 40/min.  The patient appears pale and diaphoretic and peripheral pulses are faint.  Blood pressure is 70/40 mm Hg.  Which of the following is the best immediate step for managing this patient's condition?

Quizplus · Accepted Answer

This patient with ST elevation in leads II, III, and aVF has an acute inferior wall myocardial infarction (MI), which most commonly occurs due to occlusion of the right coronary artery (RCA). The RCA usually supplies blood to the sinoatrial node, the atrioventricular node, and most of the bundle of His; therefore, conduction impairment (eg, sinus bradycardia, atrioventricular block) is common in patients with inferior wall MI. Sinus bradycardia is the most common arrhythmia in those with inferior wall MI (nearly 50% of patients); it occurs due to both nodal ischemia and enhanced vagal tone triggered by infarction of myocardial tissue. The bradycardia is usually transient and resolves with restoration of coronary blood flow; however, patients with hypotension or symptoms of bradycardia (eg, lightheadedness, syncope) should be managed with intravenous atropine. The anticholinergic effects of atropine counteract the enhanced vagal tone to increase heart rate and improve symptoms. (Choice A) Adenosine hyperpolarizes the atrioventricular node to cause transient atrioventricular conduction delay. It is useful in the treatment of paroxysmal supraventricular tachycardia, but it is likely to worsen bradycardia. (Choice B) Alteplase is a fibrinolytic agent indicated for the acute management of patients with ST-elevation MI who cannot undergo percutaneous coronary intervention (PCI) in a timely manner. PCI is associated with reduced mortality and a lower rate of complications (eg, cerebral hemorrhage) compared with fibrinolytic therapy and is the preferred intervention whenever possible. (Choice C) Amiodarone is a class III antiarrhythmic agent that can be used for the management of ventricular arrhythmia (eg, ventricular tachycardia) in patients with acute MI. However, the drug causes negative chronotropy and is not used to treat bradyarrhythmias. (Choice E) Naloxone, an opioid-receptor antagonist, is used to reverse the effects of opioid overdose (eg, somnolence, respiratory and cardiac depression). Although morphine may cause bradycardia, this patient's bradycardia is more likely due to his inferior wall MI. (Choice F) Physostigmine, an acetylcholinesterase inhibitor that prolongs the effects of acetylcholine, is used in the treatment of myasthenia gravis. Its effects essentially oppose those of atropine; it would worsen the bradycardia in this patient. Educational objective: Conduction impairment is common with acute inferior wall myocardial infarction. Sinus bradycardia often occurs due to nodal ischemia and an increase in vagal tone triggered by infarction of myocardial tissue; the enhanced vagal tone can be counteracted by the anticholinergic effects of atropine. __________ References: Early and late atrioventricular block in acute inferior myocardial infarction. (http://www.ncbi.nlm.nih.gov/pubmed/6736451) 2013 ACCF/AHA guideline for the management of ST-elevation myocardial infarction: a report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines. (http://www.ncbi.nlm.nih.gov/pubmed/23256914)

A 55-Year-Old Man Comes to the Emergency Department Due to an Hour