USMLE题库Cardiology(一)21-30.pptx

Cardiology 1 题库 Q 21 A 56-year-old man comes to the cardiology clinic because of fatigue, palpitations, and exertional dyspnea over the last several weeks. On physical examination, his heart rate is irregular and measures 122 beats per minute, while his blood pressure is 110/70 mm Hg. The patient undergoes further work-up, including ECG, radiographic studies, and laboratory studies. His ECG shows atrial fibrillation and trans-esophageal echocardiography reveals a thrombus in a dilated left atrium. In the event of an interruption of blood flow secondary to arterial occlusion, which of the following organs would be least vulnerable to infarction? A.Spleen B.Brain C.Kidney D.Liver E.Heart A 21 Correct answer:D Infarcts in an otherwise normal liver are rare because it has a dual blood supply: the portal vein and hepatic artery. Should the hepatic artery become occluded, the portal venous supply and retrograde arterial flow through accessory vessels (e.g., from the inferior phrenic, adrenal, intercostal arteries, etc.) is typically sufficient to sustain the liver parenchyma. The notable exception is when a transplanted liver undergoes hepatic artery thrombosis. In this case, the liver can develop biliary tree infarction and organ failure because the collateral blood supply is severed during transplantation. (Choice A) The spleen is relatively vulnerable to infarction because the perfusion via the splenic artery is end-arterial. Wedge-shaped, capsule-based splenic infarcts occur and are a known complication of sickle cell anemia, infective endocarditis, and cardiac mural thrombosis. (Choice B) Irreversible damage appears to occur in the most vulnerable of neurons after approximately 5 minutes of complete ischemia. (Choice C) The kidney, similar to the spleen, has an end-arterial blood supply, and is generally able to tolerate warm ischemia for at least 30 minutes. Longer periods of complete ischemia result in immediate functional loss; late recovery of renal function is i