Recurrent syncope is being evaluated in a 66-year-old man. Over the last 6 months, he has experienced three episodes of dizziness and palpitations, followed by a brief loss of consciousness. He is not experiencing any chest pain or dyspnea. The patient has a history of high blood pressure and hyperlipidemia. There is no history of sudden death in the family. The initial evaluation reveals that the ECG and echocardiogram are normal. An electrophysiologic study of the heart is performed. During the study, an intravenous infusion of a medication is given, resulting in the responses shown below. Which of the following medications was most likely administered to this patient?

Question

Recurrent syncope is being evaluated in a 66-year-old man. Over the last 6 months, he has experienced three episodes of dizziness and palpitations, followed by a brief loss of consciousness. He is not experiencing any chest pain or dyspnea. The patient has a history of high blood pressure and hyperlipidemia. There is no history of sudden death in the family. The initial evaluation reveals that the ECG and echocardiogram are normal. An electrophysiologic study of the heart is performed. During the study, an intravenous infusion of a medication is given, resulting in the responses shown below.  Which of the following medications was most likely administered to this patient?

Quizplus · Accepted Answer

Eductional Objective: The effects depicted in the graphs above are most similar to those seen with isoproterenol, a nonselective Beta adrenergic agonist. By acting on myocardial beta -1 adrenergic receptors, isoproterenol increases cardiac contractility (positive inotropic effect). It also binds to beta -2 adrenergic receptors, causing vasodilation by relaxing vascular smooth muscle, resulting in lower vascular resistance and mean arterial blood pressure. Isoproterenol has no effect on the alpha-1 adrenergic receptor.

Recurrent Syncope Is Being Evaluated in a 66-Year-Old Man