Porth's Essentials of Pathophysiology, 4e

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Disorders of Cardiac Function

C h a p t e r 1 9

Left circumflex artery

Right coronary artery

Left anterior descending artery

LV

LV

LV

FIGURE 19-4. Areas of the heart affected by occlusion of the (A)  right coronary artery, (B) left anterior descending coronary artery, and (C) left circumflex coronary artery. LV, left ventricle; RV, right ventricle.

RV

RV

RV

C

A

B

Right coronary artery obstruction

Left anterior descending coronary artery obstruction

Left circumflex coronary artery obstruction

longer interval can salvage some ischemic myocardial cells. Reestablishing blood flow may also prevent the microvascular injury that occurs over a longer period.

Even though much of the viable myocardium existing at the time reperfusion recovers, critical abnormalities in biochemical function may persist, and these changes can lead to chronic impairment of ventricular function. The recovering area of the heart is often referred to as a stunned myocardium. Because myocardial function is lost before cell death occurs, a stunned myocardium may not be capable of sustaining life, and persons with large areas of dysfunctional myocardiummay require support- ive care until the stunned regions regain their function. 6 The onset of STEMI involves abrupt and significant chest pain. The pain typically is severe, often described as being constricting, suffocating, and crushing. Substernal pain that radiates to the left arm, neck, or jaw is common, although it may be experienced in other areas of the chest and back. Unlike that of angina, the pain associated with MI is more prolonged and not relieved by rest or nitro- glycerin; this pain frequently requires morphine for relief. Some persons may not describe it as “pain,” but as “dis- comfort.” Women may experience atypical ischemic-type chest pain, whereas the elderly may complain of shortness of breath more frequently than chest pain. 17 Complaints of fatigue and weakness, especially of the arms and legs, are common. Pain and elevated sympathetic activity invoke tachycardia, anxiety, and restlessness, as well as emotional responses (e.g., a feeling of impending doom). Impairment of myocardial function may lead to hypoten- sion and shock. In addition, gastrointestinal complaints are common with acute MI. There may be a sensation of epigastric distress; nausea and vomiting may occur. These symptoms are thought to be related to the severity of the

FIGURE 19-5. Acute myocardial infarct. A cross-section of the ventricles of a man who died a few days after the onset of severe chest pain shows a transmural infarct in the posterior and septal regions of the left ventricle.The necrotic myocardium is soft, yellowish, and sharply demarcated. (From Rubin E, Farber JL. Rubin’s Pathology: Clinicopathologic Foundations of Medicine. 3rd ed. Philadelphia, PA: Lippincott Williams &Wilkins; 1999:558.)