And Microscopic Examination

Many suggestions have been made for sections to be taken for microscopic examination (3,42); most current policies are determined by the clinical history, the gross findings, special interests of the prosector (7), and cost restraints.

GENERAL RECOMMENDATIONS For operated hearts and cases with a cardiac cause of death, a photograph of the heart should be taken before its dissection is begun. Preferably, the heart should be fixed in formalin for at least 5 min (to dull the surface) and then oriented as it is normally positioned in the chest. If it is dissected by the short-axis method, at least one photograph of the largest slice should be obtained, with the specimen viewed from the apex toward the base and with a short ruler (see Fig. 3-2).

For autopsy cases with a noncardiac cause of death and a grossly normal heart, no histologic slides may be needed or only a single section from the left ventricle, preferably including one of the papillary muscles. All microscopic samples should be transmural, about 1.5 cm wide and 0.3 cm thick. Rectangular sec tions are preferred because they contain more subendocardial tissue, where ischemic injury most commonly occurs. Specimens should be labeled in detail according to their location (Fig. 3-10).

Coronary arteries and valves should be stained with Verhoff-van Gieson. For conduction tissues, a trichrome stain is optional. Routine stains suffice for most other cardiac sections. In the first week after open heart surgery, low-output failure without an obvious morphologic cause, either grossly or microscopically, is common (43).

ISCHEMIC HEART DISEASE Coronary artery disease, ischemic myocardial changes, and, in some cases, the effects of surgical and nonsurgical interventions must be evaluated (2,15, 44,45). Postmortem coronary angiography is optional; perfusion fixation is only necessary in research studies. The arteries are cut in cross sections at 3-5 mm intervals. Heavily calcified vessels should be removed and decalcified prior to sectioning. Microscopy may be performed to document chronic grade-4 obstructions and acute lesions such as plaque rupture and thrombosis (Table 3-1).

Segments with nonsurgical interventions such as percutaneous transluminal coronary angioplasty (PTCA), stent placement, or atherectomy may also be evaluated microscopically. For bypass grafts, sections should include the most obstructed areas of the graft body, coronary anastomosis, and distal coronary artery (Fig. 3-11). In most cases, all sections from one graft can be placed into one cassette (see Appendix 3-1). At the anastomosis, the coronary artery should be cut in cross-section, regardless of the angle of the graft.

Hearts should be dissected by the short-axis method (see Fig. 3-2B) (7,11,42,46,47). Only for teaching purposes are a a a a

Basal Midventricular Apical Midventricular

Fig. 3-10. Schematic diagram of the left (LV) and right (RV) ventricular regions. (A) Abbreviations for ventricular regions. (B) Three standard sections for microscopic evaluation. (A, anterior; AL, anterolateral; AS, anteroseptal; I, inferior; IL, inferolateral; IS, inferoseptal; L, lateral; P, posterior; PL, posterolateral; PS, posteroseptal; S, septal.)

Basal Midventricular Apical Midventricular

Fig. 3-10. Schematic diagram of the left (LV) and right (RV) ventricular regions. (A) Abbreviations for ventricular regions. (B) Three standard sections for microscopic evaluation. (A, anterior; AL, anterolateral; AS, anteroseptal; I, inferior; IL, inferolateral; IS, inferoseptal; L, lateral; P, posterior; PL, posterolateral; PS, posteroseptal; S, septal.)

Clinical state

Table 3-1

Correlation Between Clinical Manifestation of Coronary Artery Disease and Pathologic Features of Atherosclerotic Plaquesa

Microscopic features of coronary atherosclerosis

Asymptomatic Angina pectoris Chronic stable (exertional) Variant (Prinzmetal's) Microvascular (syndrome X)

Unstable (preinfarction)

Myocardial infarction (MI) Acute myocardial ischemiab

Acute subendocardial MI Acute transmural MI

Chronic myocardial ischemiac Old healed MI (scars > 1 cm)

Chronic heart failure

Sudden death

Stable plaques, grades 1-3; occasionally, grade 4 stable plaques (generally one-vessel disease).

Stable grade 4 plaques (usually two-vessel or three-vessel disease).

Stable plaques, of any grade; evidence of plaque progression; occasionally an unstable atheroma.

No significant disease of epicardial coronary arteries; medial and intimal thickening of intramural arteries; swollen capillary endothelial cells.

Unstable plaque, of any grade, with rupture and acute nonocclusive platelet-rich thrombus; also stable grade 4 plaques (usually three-vessel disease).

Unstable plaque, of any grade, with rupture and acute thrombus, either nonocclusive or occlusive; often associated with other stable grade 4 plaques.

Same as for unstable angina.

Unstable plaque, of any grade, with rupture and acute occlusive fibrin-rich thrombus; also stable grade 4 plaques (usually two-vessel or three-vessel disease).

Stable grade 4 plaques (usually two-vessel or three-vessel disease).

Stable grade 4 plaques (usually two-vessel or three-vessel disease); old organized thrombus, especially with transmural infarcts.

Stable grade 4 plaques (usually two-vessel or three-vessel disease); old organized thrombus; evidence of plaque progression.

Unstable plaques, of any grade, with rupture and acute thrombus, either nonocclusive or occlusive; associated with other stable grade 4 plaques (two-vessel or three-vessel disease in 80%, one-vessel disease in 15%, and four-vessel disease in 5%).

aRepresents autopsied cases only (a source of bias). See the section on "Evaluation of Coronary Arteries" for a description of the grades of obstruction. Unstable plaques are characterized by a thin fibrous cap, a large lipid-rich core, subendothelial clusters of monocytes or foam cells, atherophagocytosis, or adventitial or intimal lymphocytes.

b Characterized microscopically by contraction band necrosis or by nuclear pyknosis and intense sarcoplasmic staining with eosin, occurring in the absence of an infiltrate of neutrophils or, with reperfusion, macrophages. These features generally represent preinfarction changes in which the patient died before leukocytic infiltration occurred.

c Characterized microscopically by patchy subendocardial collections of vacuolated myocytes or by small (<1 cm) subendocardial patches of fibrosis or granulation tissue. Adapted from Edwards (15).

other methods recommended (see Fig. 3-4C). Grossly, both old and acute infarcts should be described in terms of extent (transmural or subendocardial), location (anteroseptal, inferior, or lateral), and level (apical, midventricular, or basal).

For the macroscopic demonstration of acute myocardial ischemia, various dyes have been used, the most popular of which have been nitro-blue tetrazolium (NBT) and triphenyl tetrazolium chloride (TTC) (46-49). Nevertheless, the best and least expensive method, within 4 h after injury, is a slide well-stained with hematoxylin-eosin. The microscopic features of acute and chronic myocardial ischemia (50-53) and of acute myocardial infarction of various ages (Table 3-2) (54-56), have

Your Heart and Nutrition

Your Heart and Nutrition

Prevention is better than a cure. Learn how to cherish your heart by taking the necessary means to keep it pumping healthily and steadily through your life.

Get My Free Ebook


Post a comment