A 64-year-old man comes to the emergency department due to chest discomfort and shortness of breath. Medical history includes hypertension, type 2 diabetes mellitus, and severe osteoarthritis of the left knee. The patient is an active smoker with a 20-pack-year smoking history. He undergoes dobutamine infusion with simultaneous cardiac imaging. The following is seen:Before infusion: normal left ventricular contractility, ejection fraction 60%During infusion: decreased apical contractility, ejection fraction 45%Five minutes after infusion: normal left ventricular contractility, ejection fraction 60%Which of the following best explains the observed findings?

Question

A 64-year-old man comes to the emergency department due to chest discomfort and shortness of breath.  Medical history includes hypertension, type 2 diabetes mellitus, and severe osteoarthritis of the left knee.  The patient is an active smoker with a 20-pack-year smoking history.  He undergoes dobutamine infusion with simultaneous cardiac imaging.  The following is seen:Before infusion: normal left ventricular contractility, ejection fraction 60%During infusion: decreased apical contractility, ejection fraction 45%Five minutes after infusion: normal left ventricular contractility, ejection fraction 60%Which of the following best explains the observed findings?

Quizplus · Accepted Answer

Stable angina results from fixed coronary artery stenosis in the setting of atherosclerotic coronary artery disease (CAD). Such a stenosis limits blood supply to the downstream myocardium, which, during periods of increased myocardial oxygen demand (eg, exercise), can cause a mismatch of oxygen supply and demand that manifests as anginal symptoms (eg, chest pain, shortness of breath). Pharmacologic stress testing can be useful in diagnosing atherosclerotic CAD. Dobutamine, a beta-1 agonist, increases heart rate and contractility to mimic the increase in myocardial oxygen demand that occurs with exercise. Myocardium that is unable to obtain sufficient blood flow to meet the increased oxygen demand typically demonstrates a transient decrease in contractility (ie, wall motion defect), often leading to reduced ejection fraction. This patient with a transient wall motion defect localized to the cardiac apex most likely has a fixed atherosclerotic lesion that limits blood flow to that area of myocardium. (Choice A) Coronary artery occlusion due to plaque rupture and thrombosis leads to acute myocardial infarction (MI). Because of total coronary artery occlusion and a completely blocked myocardial oxygen supply, a persistent (before, during, and after dobutamine infusion), rather than transient, wall motion defect would be expected. (Choice B) Vasospastic angina is due to coronary artery vasospasm and can mimic stable angina that results from atherosclerotic CAD; however, vasospastic angina typically occurs in relatively young patients (age <50). In addition, dobutamine has only a small agonistic effect on alpha-1 receptors and is unlikely to trigger coronary vasospasm. (Choice C) Focal myocardial fibrosis typically results from previous MI. Contractility is impaired in the fibrosed myocardium, leading to a persistent wall motion defect similar to that expected with acute MI. (Choice D) In the normal state, dobutamine boosts myocardial contractility, and the rise in myocardial oxygen demand is met by increased myocardial oxygen supply via increased blood flow. Therefore, the normal response to dobutamine infusion is a transient increase in ejection fraction. Educational objective: Stable angina results from fixed coronary artery stenosis that limits blood flow to downstream myocardium, preventing the myocardial oxygen supply from increasing during exertion. Dobutamine mimics the effects of exercise and increases myocardial oxygen demand; it can be used during stress testing to provoke areas of ischemic myocardium, which can be recognized on imaging by a localized and transient decrease in contractility (ie, wall motion defect).

A 64-Year-Old Man Comes to the Emergency Department Due to Chest