Cardiology

Answer 5 Initiate IV labetalol infusion, titrating to a target heart rate of 60 to 80 bpm and a mean arterial pressure of 60 to 80 mm Hg, and obtain emergent cardiothoracic surgical evaluation. This patient has symptoms of an acute type A aortic dissection extending into the right coronary artery, aortic valve, and aortic arch.4 A type B dissection involves the descending thoracic aorta and spares the ascending aorta and aortic arch. Clues that should raise suspicion for acute aortic dissection include uncontrolled hypertension, sharp pain radiating to the back, presence of a high-pitched diastolic murmur suggestive of aortic regurgitation, unequal blood pressures between the arms indicating compromise of the left subclavian artery, and a widened mediastinum on chest radiograph. A type A dissection almost always requires urgent surgical intervention necessitating immediate consultation with a cardiothoracic surgeon.4 In the interim, the patient should be rapidly treated with IV ß-blockade to lower blood pressure, heart rate, and shear stress on the dissecting aorta. Labetalol is a mixed α- and ß-blocker effective for lowering the blood pressure and reducing the shear stress on the aortic wall.4 Although the patient has evidence of myocardial injury, the mechanism of MI in aortic dissection is usually a result of mechanical disruption of the coronary ostium rather than an acute thrombotic process, and administration of antiplatelet agents, anticoagulation, and/or thrombolytics could prove lethal. Administering nitroprusside without concomitant ß-blockade may increase the cardiac contractility and the shear stress on the aortic wall with the potential to worsen the dissection. REFERENCE 4. Chen K, Varon J, Wenker OC, et al. Acute thoracic aortic dissection: the basics. J Emerg Med 1997;15:859–67. Click here to return to the questions

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