A 65-year-old man is brought to the emergency department due to central chest pain for the past 2 hours. The patient describes the pain as "very severe" and "going back all the way to my spine." He has never had similar pain. Medical history is significant for hypertension; the patient has been nonadherent with prescribed medical therapy and follow-up visits. He has a 20-pack-year smoking history. Blood pressure is 195/101 mm Hg, and pulse is 93/min and regular. Chest examination reveals clear lungs. ECG shows sinus rhythm and voltage criteria for left ventricular hypertrophy. Portable chest x-ray reveals a widened mediastinum. The patient is immediately treated with intravenous esmolol. Which of the following is the most likely purpose of this patient's current therapy?

Question

A 65-year-old man is brought to the emergency department due to central chest pain for the past 2 hours.  The patient describes the pain as "very severe" and "going back all the way to my spine."  He has never had similar pain.  Medical history is significant for hypertension; the patient has been nonadherent with prescribed medical therapy and follow-up visits.  He has a 20-pack-year smoking history.  Blood pressure is 195/101 mm Hg, and pulse is 93/min and regular.  Chest examination reveals clear lungs.  ECG shows sinus rhythm and voltage criteria for left ventricular hypertrophy.  Portable chest x-ray reveals a widened mediastinum.  The patient is immediately treated with intravenous esmolol.  Which of the following is the most likely purpose of this patient's current therapy?

Quizplus · Accepted Answer

This patient's severe chest pain radiating to the back and a widened mediastinum on chest x-ray are consistent with acute aortic dissection. Uncontrolled hypertension, suggested by the patient's nonadherence with medical therapy and ECG evidence of left ventricular (LV) hypertrophy, is the strongest risk factor for aortic dissection. With each LV contraction, the ejected stroke volume rapidly increases aortic pressure and generates shear stress on the aortic wall. Medical therapy for aortic dissection is aimed at reducing aortic wall shear stress to limit extension of the dissection. This is accomplished via anti-impulse therapy to decrease the rate of change in aortic blood pressure per time (ie, reduce dP/dt). Esmolol is a selective beta-1 receptor blocker that is given by intravenous infusion. It is first-line therapy for acute aortic dissection as it has a short half-life (allowing for easy dose titration) and reduces shear stress in 2 ways: Negative inotropy decreases LV contraction velocity. This decreases the rate of blood ejection and reduces stroke volume (Choice E) to decrease the rise in blood pressure with each contraction (ie, decreased rate and magnitude of blood pressure change). Negative chronotropy decreases heart rate, subjecting the aortic wall to fewer LV contractions per minute (ie, decreased number of blood pressure changes). Once shear stress has been minimized with adequate reduction in LV contractility and heart rate, decreasing peripheral vascular resistance (PVR) to further reduce blood pressure is also beneficial. Because esmolol has little effect on PVR (Choice C), vasodilators (eg, nitroprusside, nicardipine) may be added for this purpose. Vasodilators should never be given prior to a negative chronotropic agent because vasodilation causes reflex tachycardia that increases aortic wall shear stress. (Choice B) Reduced LV contractility and heart rate decrease myocardial oxygen demand. Although this is the major goal of medical therapy for treating myocardial ischemia, reducing aortic wall shear stress is much more important for treating aortic dissection. (Choice D) Reduced LV contractility and heart rate may slightly increase LV filling pressure (due to less blood being ejected with each contraction and increased LV filling time), but this effect is of minimal consequence in treating aortic dissection. Educational objective: The primary goal of medical therapy for acute aortic dissection is to reduce aortic wall shear stress by minimizing the change in aortic blood pressure per time (dP/dt). Esmolol, a selective beta-1 receptor blocker, decreases left ventricular contraction velocity and heart rate to reduce dP/dt. __________ References: Managing dissections of the thoracic aorta. (http://www.ncbi.nlm.nih.gov/pubmed/18481490)

A 65-Year-Old Man Is Brought to the Emergency Department Due