05 Cat. Cardiovascular I

Figure 12-1 Myocardium (cardiac muscle). A The histology of myocardium is shown, emphasizing the centrally-placed nuclei of the cardiac myocytes (arrowhead), intercalated discs (representing specialized end-to-end junctions of adjoining cells; highlighted by a double arrow) and the sarcomeric structure visible as cross-striations within myocytes. A capillary endothelial cell is indicated by an arrow. (Photomicrograph courtesy of Mark Flomenbaum, M.D., Ph.D., Office of the Chief Medical Examiner, New York City, NY.) B Electron microscopy of myocardium, showing myofibrillar (my) and mitochondrial (mi) architecture and the sarcolemmal membrane (s). Z bands are indicated by arrows. Bar = 1 μm. (Reproduced by permission from Vivaldi MT, et al. Triphenyltetrazolium staining of irreversible injury following coronary artery occlusion in rats. Am J Pathol 121:522, 1985. Copyright J.B. Lippincott, 1985.) The normal heart weight  250 to 300 g females and 300 to 350 g males. Thickness of the free wall of the right ventricle is 0.3 to 0.5 cm and that of the left ventricle 1.3 to 1.5 cm. Greater heart weight or ventricular thickness indicates hypertrophy, and an enlarged chamber size implies dilation . An increase in cardiac weight or size is termed cardiomegaly .

Figure 12-2 Aortic valve histology, shown as a low-magnification photomicrograph of cuspal cross-section in the systolic (nondistended) state, emphasizing three major layers (ventricularis [v], spongiosa [s], and fibrosa [f]). Superficial endothelial cells (arrow) and diffusely distributed deep interstitial cells are noted. The strength of the valve is predominantlyderived from the fibrosa, with its dense collagen (yellow) . This section highlights the dense, laminated elastic tissue in the ventricularis (double arrow) . The outflow surface is at top. (Reproduced by permission from Schoen FJ: Aortic valve structure-function correlations: Role of elastic fibers no longer a stretch of the imagination. J Heart Valve Dis 6:1, 1997.)

TABLE 12-1 -- Changes in the Aging Heart Increased cross-sectional luminal area Tortuosity Epicardial Coronary Arteries Lambl excrescences Buckling of mitral leaflets toward the left atrium Fibrous thickening of leaflets Mitral valve annular calcific deposits Aortic valve calcific deposits Valves Sigmoid-shaped ventricular septum Decreased left ventricular cavity size Increased left atrial cavity size Chambers

Atherosclerotic plaque Elastic fragmentation and collagen accumulation Sinotubular junction calcific deposits Elongated (tortuous) thoracic aorta Dilated ascending aorta with rightward shift Aorta Amyloid deposits Basophilic degeneration Lipofuscin deposition Brown atrophy Increased subepicardial fat Increased mass Myocardium Atherosclerotic plaque Calcific deposits

• Failure of the pump . In the most common circumstance, the cardiac muscle contracts weakly or inadequately, and the chambers cannot empty properly. In some conditions, however, the muscle cannot relax sufficiently to permit ventricular filling. • An obstruction to flow , owing to a lesion preventing valve opening or otherwise causing increased ventricular chamber pressure (e.g., aortic valvular stenosis, systemic hypertension, or aortic coarctation). The increased pressure overworks the chamber that pumps against the obstruction. • Regurgitant flow causes some of the output from each contraction to flow backward, adding a volume workload to each of the chambers, which must pump the extra blood (e.g., left ventricle in aortic regurgitation; left atrium and left ventricle in mitral regurgitation). • Disorders of cardiac conduction . Heart block or arrhythmias owing to uncoordinated generation of impulses (e.g., atrial or ventricular fibrillation) lead to nonuniform and inefficient contractions of the muscular walls. • Disruption of the continuity of the circulatory system that permits blood to escape (e.g., gunshot wound through the thoracic aorta).

• The Frank-Starling mechanism , in which the increased preload of dilation (thereby increasing cross-bridges within the sarcomeres) helps to sustain cardiac performance by enhancing contractility • Myocardial structural changes, including augmented muscle mass (hypertrophy) with or without cardiac chamber dilation , in which the mass of contractile tissue is augmented • Activation of neurohumoral systems , especially (1) release of the neurotransmitter norepinephrine by adrenergic cardiac nerves (which increases heart rate and augments myocardial contractility and vascular resistance), (2) activation of the renin-angiotensin-aldosterone system, and (3) release of atrial natriuretic peptide.

Figure 12-3 Left ventricular hypertrophy. A, Pressure hypertrophy due to left ventricular outflow obstruction. The left ventricle is on the lower right in this apical four-chamber view of the heart. B, Altered cardiac configuration in left ventricular hypertrophy without and with dilation, viewed in transverse heart sections. Compared with a normal heart ( center ), the pressurehypertrophied hearts ( left and in A ) have increased mass and a thick left ventricular wall, but the hypertrophied and dilated heart (right) has increased mass but a normal wall thickness. (Reproduced by permission from Edwards WD: Cardiac anatomy and examination of cardiac specimens. In Emmanouilides GC, Riemenschneider TA, Allen HD, Gutgesell HP (eds): Moss and Adams Heart Disease in Infants, Children, and Adolescents: Including the Fetus and Young Adults, 5th ed. Philadelphia, Williams and Wilkins, 1995, p. 86.)

Figure 12-4 Schematic representation of the sequence of events in cardiac hypertrophy and its progression to heart failure, emphasizing cellular and extracellular changes.

The most frequent causes of the major functional valvular lesions are as follows: • Aortic stenosis : calcification of anatomically normal and congenitally bicuspid aortic valves • Aortic insufficiency : dilation of the ascending aorta, related to hypertension and aging. • Mitral stenosis: rheumatic heart disease • Mitral insufficiency: myxomatous degeneration (mitral valve prolapse)

Figure 12-22 Calcific valvular degeneration. A, Calcific aortic stenosis of a previously normal valve having three cusps (viewed from aortic aspect). Nodular masses of calcium are heapedup within the sinuses of Valsalva (arrow) . Note that the commissures are not fused, as in postrheumatic aortic valve stenosis (see Fig. 12-24 E ). B, Calcific aortic stenosis occurring on a congenitally bicuspid valve. One cusp has a partial fusion at its center, called a raphe (arrow). C and D, Mitral annular calcification, with calcific nodules at the base (attachment margin) of the anterior mitral leaflet (arrows) . C, Left atrial view. D, Cut section of myocardium.

Figure 12-23 Myxomatous degeneration of the mitral valve. A, Long axis of left ventricle demonstrating hooding with prolapse of the posterior mitral leaflet into the left atrium (arrow) . The left ventricle is on right in this apical four-chamber view. (Courtesy of William D. Edwards, M.D., Mayo Clinic, Rochester, MN.) B, Opened valve, showing pronounced hooding of the posterior mitral leaflet with thrombotic plaques at sites of leaflet-left atrium contact (arrows). C , Opened valve with pronounced hooding from patient who died suddenly (double arrows) . Note also mitral annular calcification (arrowhead) .

Figure 12-12 Schematic representation of sequential progression of coronary artery lesion morphology, beginning with stable chronic plaque responsible for typical angina and leading to the various acute coronary syndromes. (Modified and redrawn from Schoen FJ: Interventional and Surgical Cardiovascular Pathology: Clinical Correlations and Basic Principles. Philadelphia, W.B. Saunders Co., 1989, p. 63.)

Figure 12-11 Atherosclerotic plaque rupture. A, Plaque rupture without superimposed thrombus, in patient who died suddenly. B, Acute coronary thrombosis superimposed on an atherosclerotic plaque with focal disruption of the fibrous cap, triggering fatal myocardial infarction. C, Massive plaque rupture with superimposed thrombus, also triggering a fatal myocardial infarction (special stain highlighting fibrin in red). In both A and B, an arrow points to the site of plaque rupture. (B, reproduced from Schoen FJ: Interventional and Surgical Cardiovascular Pathology: Clinical Correlations and Basic Principles. Philadelphia, W.B. Saunders, 1989, p. 61.)

Figure 12-13 Postmortem angiogram showing the posterior aspect of the heart of a patient who died during the evolution of acute myocardial infarction, demonstrating total occlusion of the distal right coronary artery by an acute thrombus (arrow) and a large zone of myocardial hypoperfusion involving the posterior left and right ventricles, as indicated by arrowheads, and having almost absent filling of capillaries, that is, less white. The heart has been fixed by coronary arterial perfusion with glutaraldehyde and cleared with methyl salicylate, followed by intracoronary injection of silicone polymer. Photograph courtesy of Lewis L. Lainey. (Reproduced by permission from Schoen FJ: Interventional and Surgical Cardiovascular Pathology: Clinical Correlations and Basic Principles. Philadelphia, WB Saunders, 1989, p. 60.) TABLE 12-4 -- Approximate Time of Onset of Key Events in Ischemic Cardiac Myocytes ATP, adenosine triphosphate. >1 hr Microvascular injury 20–40 min Irreversible cell injury 40 min •• to 10% of normal 10 min •• to 50% of normal ATP reduced <2 min Loss of contractility Seconds Onset of ATP depletion Time Feature

Figure 12-14 Schematic representation of the progression of myocardial necrosis after coronary artery occlusion. Necrosis begins in a small zone of the myocardium beneath the endocardial surface in the center of the ischemic zone. This entire region of myocardium (shaded) depends on the occluded vessel for perfusion and is the area at risk. Note that a very narrow zone of myocardium immediately beneath the endocardium is spared from necrosis because it can be oxygenated by diffusion from the ventricle. The end result of the obstruction to blood flow is necrosis of the muscle that was dependent on perfusion from the coronary artery obstructed. Nearly the entire area at risk loses viability. The process is called myocardial infarction, and the region of necrotic muscle is a myocardial infarct .

Figure 12-15 Acute myocardial infarct, predominantly of the posterolateral left ventricle, demonstrated histochemically by a lack of staining by the triphenyltetrazolium chloride (TTC) stain in areas of necrosis (arrow) . The staining defect is due to the enzyme leakage that follows cell death. Note the myocardial hemorrhage at one edge of the infarct that was associated with cardiac rupture, and the anterior scar (arrowhead) , indicative of old infarct. (Specimen the oriented with the posterior wall at the top.)

Figure 12-16 Microscopic features of myocardial infarction and its repair. A, One-day-old infarct showing coagulative necrosis along with wavy fibers (elongated and narrow), compared with adjacent normal fibers (at right). Widened spaces between the dead fibers contain edema fluid and scattered neutrophils. B, Dense polymorphonuclear leukocytic infiltrate in area of acute myocardial infarction of 3 to 4 days' duration. C, Nearly complete removal of necrotic myocytes by phagocytosis (approximately 7 to 10 days). D, Granulation tissue characterized by loose collagen and abundant capillaries. E, Well-healed myocardial infarct with replacement of the necrotic fibers by dense collagenous scar. A few residual cardiac muscle cells are present.

Grupo 1  Arritmias Grupo 2  Factores congénitos

Figure 12-5 Cardiac defects related to neural crest abnormalities. A, Biologic pathways for cardiac neural crest-related defects. B, Disease phenotypes. DORV, double-outlet right ventricle; TGA, transposition of the great arteries. (Reproduced by permission from Chien KR: Genomic circuits and the integrative biology of cardiac diseases. Nature 407:227, 2000.)

Figure 12-6 Schematic diagram of congenital left-to-right shunts. A, Atrial septal defect (ASD). B, Ventricular septal defect (VSD). With VSD the shunt is left-to-right, and the pressures are the same in both ventricles. Pressure hypertrophy of the right ventricle and volume hypertrophy of the left ventricle are generally present. C, Patent ductus arteriosus (PDA). D, Atrioventricular septal defect (AVSD). E, Large VSD with irreversible pulmonary hypertension. The shunt is right-to-left (shunt reversal). Volume hypertrophy and pressure hypertrophy of the right ventricle are present. Arrow indicates the direction of blood flow. The right ventricular pressure is now sufficient to yield a right-to-left shunt (Ao, aorta; LA, left atrium; LV, left ventricle; PT, pulmonary trunk; RA, right atrium; RV, right ventricle.)

Figure 12-7 Gross photograph of a ventricular septal defect (membranous type); defect denoted by arrow. (Courtesy of William D. Edwards, M.D., Mayo Clinic, Rochester, MN.)

Figure 12-8 Schematic diagram of the most important right-to-left shunts (cyanotic congenital heart disease) . A, Tetralogy of Fallot. Diagrammatic representation of anatomic variants, indicating that the direction of shunting across the VSD depends on the severity of the subpulmonary stenosis. Arrows indicate the direction of the blood flow. B, Transposition of the great vessels with and without VSD. (Ao, aorta; LA, left atrium; LV, left ventricle; PT, pulmonary trunk; RA, right atrium; RV, right ventricle.) (Courtesy of William D. Edwards, M.D., Mayo Clinic, Rochester, MN.)

Figure 12-9 Transposition of the great arteries. (Courtesy of William D. Edwards, M.D., Mayo Clinic, Rochester, MN.) Figure 12-10 Diagram showing coarctation of the aorta with and without PDA. (Ao, aorta; LA, left atrium; LV, left ventricle; PT, pulmonary trunk; RA, right atrium; RV, right ventricle; PDA, persistent ductus arteriosus.) (Courtesy of William D. Edwards, M.D., Mayo Clinic, Rochester, MN.)

05 Cat. Cardiovascular I

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05 Cat. Cardiovascular I