IPLab:Lab 3:Healed Myocardial Infarction

Clinical Summary

This 37-year-old white female with a 22 year history of insulin-dependent diabetes was admitted to the hospital 10 hours prior to death complaining of chest pain and shortness of breath. Three months before, she had begun to experience progressive weakness and for the previous 3 weeks she noticed increasing dyspnea on exertion and worsening of a chronic cough.

Autopsy Findings

Autopsy showed a 340-gram heart with extensive transmural reddish discoloration of the anterolateral portion of the myocardium of the left ventricle. There was severe atherosclerotic narrowing of all coronary arteries especially the left anterior descending. The lungs showed pulmonary edema and early bronchopneumonia.

Images

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  This is a gross photograph of a heart with areas of old healed myocardial infarction (scars) outlined by arrows.

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  This is a low-power photomicrograph of a healed myocardial infarction with a fibrous scar. Remaining normal tissue is on the left (1) and the fibrous connective tissue scar is on the right (2).

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  This is a higher-power photomicrograph of a healed myocardial infarction with a fibrous scar. Remaining normal tissue is at the top (1) and the fibrous connective tissue scar is at the bottom (2). Note the presence of occasional hypereosinophilic myocytes indicating recent acute ischemic injury to this region of old scar tissue (arrows).

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  This is another high-power photomicrograph of a healed myocardial infarction. Note the remaining normal myocytes (1), the fibrous connective tissue (2), and occasional hypereosinophilic myocytes indicating recent acute ischemic injury (arrow).

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  This is a low-power photomicrograph of two sections of myocardial tissue stained with a trichrome stain to demonstrate fibrous connective tissue (blue). The section on the left is from a heart with a recent myocardial infarction. Notice the absence of fibrous connective tissue. The section on the right is from a heart with an old healed infarct and it contains extensive fibrous connective tissue scars.

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  This is a photomicrograph of a trichrome-stained section from a heart with an acute myocardial infarction. Note that there is little fibrous connective tissue. It is too early for scar formation to have taken place in this acute lesion.

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  This is a photomicrograph of a trichrome-stained section of heart containing an old healed myocardial infarction. The scar is composed of mature fibrous connective tissue (arrows).

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  This is a higher-power photomicrograph of a trichrome-stained section of heart containing an old healed MI. The scar tissue (mature fibrous connective tissue) is stained blue.

Study Questions

• Why does this 37-year-old woman have such severe coronary atherosclerosis?

Diabetes mellitus is a major risk factor for developing premature atherosclerosis.

• Why are there areas of acute myocardial injury in the section of myocardium from the patient with the old healed myocardial infarction?

This finding is very common in areas adjacent to an old infarction. If you remember from previous cases, there were areas of vacuolar change adjacent to the acute infarct. The areas adjacent to an infarct may still be alive but they will be at risk for additional ischemic insult. In this current case, the patient had several serious medical problems which may have caused hypotension and poor perfusion to the heart. Thus, the areas of risk could have been damaged leading to acute myocardial necrosis.

• What is the time course of the normal inflammatory response after a myocardial infarction?

Few morphologic changes occur in the heart until approximately 6 to 12 hours after coronary occlusion. Subtle changes such as hypereosinophilia, coagulation necrosis and wavy fiber change can be seen during this early time period. If there is reperfusion of the myocardium there may be contraction band necrosis as well.

By two to three days there is an acute inflammatory cell infiltrate comprising primarily neutrophils.

At 5 to 10 days macrophages come in to phagocytose the necrotic myocardial tissue. As the dead tissue is being phagocytosed by macrophages, fibroblasts and blood vessels begin to grow into the area of infarction and form granulation tissue.

Fibroblasts lay down collagen and by two to three months the infarct is replaced by matured collagenous "scar" tissue.