A 58-year-old man with dyspnea and chronic exertional angina is evaluated for coronary revascularization. He has a history of hypertension, type 2 diabetes mellitus, and hypercholesterolemia. His blood pressure is 130/80 mm Hg and pulse is 72/min and regular. Cardiopulmonary examination is normal with the exception of a fourth heart sound. Echocardiogram reveals hypokinesia of the anterior wall of the left ventricle and a left ventricular ejection fraction (LVEF) of 35%. The patient undergoes coronary artery bypass grafting. Repeat echocardiogram 10 days after the surgery shows that hypokinesia is no longer evident and LVEF has increased to 50%. Which of the following best explains the changes in the cardiac contractility and wall motion seen in this patient?

Question

A 58-year-old man with dyspnea and chronic exertional angina is evaluated for coronary revascularization.  He has a history of hypertension, type 2 diabetes mellitus, and hypercholesterolemia.  His blood pressure is 130/80 mm Hg and pulse is 72/min and regular.  Cardiopulmonary examination is normal with the exception of a fourth heart sound.  Echocardiogram reveals hypokinesia of the anterior wall of the left ventricle and a left ventricular ejection fraction (LVEF) of 35%.  The patient undergoes coronary artery bypass grafting.  Repeat echocardiogram 10 days after the surgery shows that hypokinesia is no longer evident and LVEF has increased to 50%.  Which of the following best explains the changes in the cardiac contractility and wall motion seen in this patient?

Quizplus · Accepted Answer

Myocardial hibernation refers to a state of chronic myocardial ischemia in which both myocardial metabolism and function are reduced to match a concomitant reduction in coronary blood flow (due to moderate/severe flow-limiting stenosis). This new equilibrium prevents myocardial necrosis. Chronically hibernating myocardium demonstrates decreased expression and disorganization of contractile and cytoskeletal proteins, altered adrenergic control, and reduced calcium responsiveness. These changes lead to decreased contractility and left ventricular (LV) systolic dysfunction. However, coronary revascularization and subsequent restoration of blood flow to hibernating myocardium improves contractility and LV function. (Choice B) Ischemic preconditioning is a phenomenon in which brief repetitive episodes of myocardial ischemia, followed by reperfusion, protect the myocardium from subsequent prolonged episodes of ischemia. In clinical terms, repetitive episodes of angina prior to myocardial infarction can delay cell death after complete coronary occlusion and therefore provide greater time for myocardial salvage with coronary revascularization. (Choice C) Post-infarction myocardial scarring refers to the replacement of myocardium with collagen and fibrous tissue. This leads to complete loss of myocardial contractile function, and cardiac contractility would not be expected to improve with coronary revascularization. (Choice D) Reperfusion injury refers to further myocardial cell damage due to restoration of blood flow after a sudden ischemic event. The clinical manifestations of reperfusion injury include arrhythmias, microvascular dysfunction with myocardial stunning, and myocyte injury and death. (Choice E) Ventricular remodeling refers to a change in the structure (cardiac mass or dimensions) or function of the heart in response to cardiac injury or hemodynamic changes (pressure/volume overload). Remodeling can occur with long-term myocardial hibernation, but it would take weeks to months (not days) to recover following reperfusion therapy. Educational objective: Hibernating myocardium refers to the presence of left ventricular systolic dysfunction due to reduced coronary blood flow at rest that is partially or completely reversible by coronary revascularization. __________ References: The hibernating myocardium in ischaemia and congestive heart failure. (http://www.ncbi.nlm.nih.gov/pubmed/8370358)

A 58-Year-Old Man with Dyspnea and Chronic Exertional Angina Is