Ruth Pick

Collagen remodeling of the pressure-overloaded, hypertrophied nonhuman primate myocardium.

Cardiac muscle is tethered within a fibrillar collagen matrix that serves to maximize force generation. In the human pressure-overloaded, hypertrophied left ventricle, collagen concentration is known to be increased; however, the structural and biochemical remodeling of collagen and its relation to cell necrosis and myocardial mechanics is less clear. Accordingly, this study was undertaken in a nonhuman primate model of left ventricular hypertrophy caused by gradual onset experimental hypertension. The amount of collagen, its light microscopic features, and proportions of collagen types I, III, and V were determined together with diastolic and systolic mechanics of the intact ventricle during the evolutionary, early, and late phases of established left ventricular hypertrophy (4, 35, and 88 weeks, respectively). In comparison to controls, we found 1) increased collagen at 4 weeks, as well as a greater proportion of type III, in the absence of myocyte necrosis; 2) collagen septae were thick and dense at 35 weeks, while the proportion of types I and III had converted to control; 3) necrosis was evident at 88 weeks, and the structural remodeling and proportion of collagen types I and III reflected the extent of scar formation; and 4) unlike diastolic myocardial stiffness, which was unchanged at 4, 35, or 88 weeks, the systolic stress-strain relation of the myocardium was altered in either a beneficial or detrimental manner in accordance with structural remodeling of collagen and scar formation. Thus, early in left ventricular hypertrophy, reactive fibrosis and collagen remodeling occur in the absence of necrosis while, later on, reparative fibrosis is present. In this study, the remodeled collagen matrix appeared responsible for variations in force generation observed during various phases of left ventricular hypertrophy.

Morphology and significance of the Left ventricular collagen network in young patients with hypertrophic cardiomyopathy and sudden cardiac death

BACKGROUNDnHypertrophic cardiomyopathy (HCM) is a primary cardiac disease with a diverse clinical spectrum, in which many of the abnormal structural and pathophysiologic features are consequences of inappropriate left ventricular hypertrophy.nnnMETHODSnWe analyzed the amount, distribution and structure of the cardiac collagen network in transmural sections of the ventricular septum (thickness 17 to 40 mm, mean 25 mm) in 16 previously asymptomatic children and young adults with HCM (11 to 31 years of age, mean 20 years) who died suddenly. The morphologic appearance and volume fractions of interstitial (matrix) and perivascular (adventitial) collagen were analyzed with polarization microscopy and computerized videodensitometry in picrosirius red-stained sections. Findings were compared with 16 structurally normal hearts, 5 with systemic hypertension and 6 infants who died of HCM.nnnRESULTSnAdults and young children with HCM had an eightfold greater amount of matrix collagen compared with normal controls (14.1 +/- 8.8% vs. 1.8 +/- 1% of the tissue section; p < 0.0001), and a threefold increase compared with patients with systemic hypertension (4.5 +/- 1.3%; p < 0.001) and infants with HCM (4.0 +/- 2.4%; p < 0.001). Compared with normal controls and hypertensives, adults and young children (and infants) with HCM showed increased numbers and thickness of each collagen fiber component of the matrix (perimysial coils, pericellular weaves and struts), which were often arranged in disorganized patterns. In HCM patients, the amount of collagen was not a consequence of other clinical, demographic and morphologic disease variables.nnnCONCLUSIONSnLeft ventricular collagen matrix in young, previously asymptomatic patients with HCM who died suddenly is morphologically abnormal and substantially increased in size. The enlarged matrix collagen compartment is present in HCM at an early age, further expands during growth, is partially responsible for increased ventricular septal thickness and likely represents a primary morphologic abnormality in this disease. These findings support the view that the complex HCM disease process is not confined to sarcomere protein abnormalities, but also involves connective tissue elements.

Fibrosis-induced reduction of endomyocardium in the rat after isoproterenol treatment.

Isoproterenol treatment leads to endomyocardial fibrosis with muscle fibers encircled by fibrillar collagen. This study was undertaken in the rat to determine if muscle encased in collagen would subsequently become either necrotic or atrophic. For this purpose, we monitored the fibrillar nature of myocardial collagen, its alignment with muscle, and the morphology of the endomyocardium, together with the response in diastolic and systolic myocardial stiffness, immediately on completion (10 days) and 30 days after a course of subcutaneous isoproterenol (500 micrograms/kg/day). We found 1) left ventricular hypertrophy at 10 and 30 days with an increase in collagen volume fraction (p less than 0.01) that consisted of a meshwork of thick and thin collagen fibers that encircled endomyocardial muscle, 2) a variable reduction in endocardial muscle fiber diameter at 30 days with the greatest thinning seen in muscle encircled by fibrous tissue, and 3) an elevation (p less than 0.01) in the slope of the diastolic stress-strain relation at 10 and 30 days. The developed systolic stress-strain relation, which was elevated at 10 days (p less than 0.01), declined (p less than 0.05) with the reduction in endomyocardial muscle mass. Thus, endomyocardial muscle, encircled by fibrillar collagen, will atrophy over time, and this leads to a reduction in active stiffness. These findings may, in part, explain why progressive ventricular dysfunction accompanies chronic myocardial disease with endomyocardial fibrosis.

Deleterious Effects of Hypertension on the Development of Aortic and Coronary Atherosclerosis in Stumptail Macaques (Macaca Speciosa) on an Atherogenic Diet

Utilizing the stumptail macaque, we studied the atherosclerotic lesions produced in the aorta and coronary arteries by an atherogenic diet alone and by the diet coupled with hypertension produced by a modified Goldblatt technique. One group of monkeys was subjected concomitantly to the diet and hypertension for 10–12 months; a second group was on the diet for 29–32 months, but hypertension was induced for only the last 7–9 months of this period. In both of these groups, hypertension led to more severe lesions in the aorta. When an index of coronary involvement was plotted as a function of either arterial systolic or diastolic blood pressure, a significant correlation was found in both groups of monkeys. Additionally, in the monkeys with hypertension, morphologic criteria indicated that increased amounts of elastic fibers were present in the plaques in a disorganized, fragmented manner; in the monkeys on the diet alone, the elastic fibers were disposed in well-formed, reduplicated lamellas. Fat deposition was also different between these two groups: fat was located in the depths and at the periphery of the lesions in the hypertensive monkeys, whereas it was evenly dispersed throughout the plaques in the monkeys on the atherogenic diet alone. Thus, hypertension coupled with an atherogenic diet increases the extent of aortic and coronary lesions in proportion to the elevation in arterial blood pressure and, furthermore, may modify the morphologic characteristics of the lesions.

The production of acute pericardial effusion: the effects of various degrees of interference with venous blood and lymph drainage from the heart muscle in the dog.

Abstract Obstruction to the venous blood and lymph outflow from the heart muscle leads to the formation of a pericardial effusion originating primarily from the epicardial surface of the heart (the visceral pericardium). The degree of effusion is proportionate to the extent of interference with the venous blood and lymph flow. Pathologic changes found in the myocardium include venous and lymphatic congestion, perivascular and interstitial edema, and early myocardial necrosis. These studies have defined a method of producing an acute pericardial effusion in the dog and clarify certain aspects of the mechanism of formation of pericardial effusions. It is considered likely that all pericardial effusions, irrespective of cause, arise primarily from the epicardial surface (visceral pericardium) of the heart.

Expression of FAS adjacent to fibrotic foci in the failing human heart is not associated with increased apoptosis.

Fibrosis in the heart may result from loss of myocytes, which are replaced by collagens. Apoptosis is now known to contribute to myocyte loss in the failing human heart. The mechanisms underlying the induction of cardiomyocyte apoptosis, and thus the expansion of fibrotic foci in the failing heart, are poorly understood. We hypothesized that viable heart cells adjacent to fibrotic foci might become predisposed to apoptosis by expression of the receptor FAS (APO1, CD95). We therefore studied the spatial relationship of FAS expression and fibrosis in patients with heart failure. Left ventricular biopsies were obtained from seven patients undergoing coronary artery bypass grafting. All patients had reduced ejection fraction but varied in New York Heart Association class score at the time of surgery. Heart cell apoptosis, fibrosis, and FAS expression were studied by propidium iodide and in situ end labeling (ISEL) of DNA, Picrosirius red staining, and immunohistochemistry. All patient samples exhibited, albeit to varying degrees, apoptosis detected by ISEL, chromatin condensation, and nuclear fragmentation. In all samples, fibrosis (collagen) was evident both perivascular and in isolated regions of scarring. Regardless of the extent of fibrosis or detectable apoptosis, FAS expression was observed in regions immediately adjacent to the fibrosis, but not in regions distal to fibrosis, nor in fibrotic areas devoid of nuclei. Expression of FAS was found adjacent to both perivascular and diffuse fibrosis, and ISEL-positive nuclei were found within cells reacting positively with anti-FAS antibodies. However, ISEL-positive nuclei were no more abundant in FAS-positive regions (67.6 +/- 5.8% of total nuclei) than in FAS-negative areas (69.5 +/- 9.8%). We conclude that expression of FAS occurs in remaining heart cells adjacent to fibrosis of either perivascular or presumed reparative origin. Although this phenomenon could contribute to the expansion of fibrotic foci, FAS-induced apoptosis in the failing heart may not be more prevalent than apoptosis initiated by other signaling mechanisms.

Editorial The Importance of the Lymphatics of the Mammalian Heart: Experimental Observations and Some Speculations

THE FACT that mammalian hearts have lymphatics has been known for a long time. Rudbeck1 first mentioned them in 1653. The most recent careful anatomic study was reported in 1939,2 with a considerable number of anatomic studies published during the almost 300 intervening years. In 1940 Drinker and his group3 published their pioneer studies on cardiac lymph obtained in the dog. They believed that the lymphatic system of the heart could have a major role in this organs metabolic economy, even as had been proved for other organs in the body. Nevertheless, to the best of our knowledge, the lymphatic system of the mammalian heart has been almost completely ignored by modern investigators of cardiac physiology and pathology. In 1954 Rusznyak and his co-workers 4 published their pathologic findings in dogs subjected to obstruction of the cardiac lymph outflow, with and without simultaneous occlusion of the coronary venous sinus. Their technic of obstructing cardiac lymph drainage included occlusion of the thoracic duct. In these animals, kept alive up to 2 weeks after surgery, they reported finding cardiac interstitial edema, frequently with visibly di-

The effects of chronic impairment of cardiac lymph flow on myocardial reactions after coronary artery ligation in dogs

Abstract Myocardial changes after an acute coronary arterial occlusion have been studied in two groups of dogs. In one group, obstruction to the cardiac lymphatic drainage had been produced prior to the coronary occlusion. In the second group, no such obstruction to lymph flow was induced. The myocardial changes in the two groups were different, especially with regard to the extent of necrosis, the sequence of inflammatory reactions, and the degree of fibrotic and calcific change. Significantly different also were the reactions in the tissues around the silk used to ligate the coronary artery branch. Characteristically, dogs with obstruction to cardiac lymphatic drainage had increased inflammatory response to the presence of this foreign body; resolution of this inflammatory response was interrupted about 40 days postoperatively by an influx of PMNs. The possible role of obstruction to cardiac lymphatic drainage in predisposing the human heart to infection and inflammation is suggested.

Relation of Thallium Uptake to Morphologic Features of Chronic Ischemic Heart Disease: Evidence for Myocardial Remodeling in Noninfarcted Myocardium

OBJECTIVESnThe aim of this study was to investigate the disparity between the extent of myocardial injury as assessed by thallium and the severity of left ventricular (LV) dysfunction in chronic ischemic heart disease.nnnBACKGROUNDnAlthough it is believed that thallium differentiates between viable and nonviable myocardium, in some patients with chronic ischemic heart disease, viable regions by thallium may fail to improve function after revascularization.nnnMETHODSnThirteen transplant candidates with chronic ischemic heart disease (LV ejection fraction = 14 +/- 6% at rest) were studied prospectively with stress-redistribution-reinjection thallium single-photon emission computed tomography. We examined pretransplantation quantitative thallium uptake and post-transplantation extent and the histological distribution of collagen replacement in infarcted and noninfarcted myocardium and in 13 age-matched control hearts.nnnRESULTSnThe volume fraction of collagen varied inversely with wall thickness (r = -0.70, p < 0.001) and was higher in irreversible (30.9 +/- 15.8%) compared with reversible (20.2 +/- 12.6%, p < 0.001) or normal thallium segments (15.0 +/- 8.7%, p < 0.001). The irreversible thallium segments had lower wall thickness and more severe coronary artery narrowing (9.7 +/- 2.8 mm and 95 +/- 8%) compared with reversible (11.7 +/- 2.7 mm and 87 +/- 13%, p < 0.001) and normal thallium segments (12.8 +/- 2.6 mm and 80 +/- 14%, p < 0.001). Mean volume fraction of collagen was significantly lower in noninfarcted than it was in infarcted segments (13 +/- 6% vs. 36 +/- 13%, p < 0.001) but exceeded that in the control hearts (4 +/- 2%, p < 0.001). Noninfarcted segments had predominantly interstitial fibrosis with either microscopic or patchy areas of replacement fibrosis.nnnCONCLUSIONSnIn chronic ischemic heart disease with severe LV dysfunction, patterns of normal, reversible and irreversible thallium uptake correlated with the magnitude of collagen replacement, segmental wall thickness and severity of coronary artery narrowing. The finding of scattered areas of replacement fibrosis in noninfarcted myocardium may explain the observed disparity between LV contractile dysfunction and the extent of myocardial injury assessed by thallium.

Myocardial pathology after cardiac venous and lymph flow obstruction in the dog

Summary This study, carried out in dogs, was designed to elucidate the effects of cardiac lymphatic and venous obstruction, both separate and combined, on the viability of the myocardium. Specimens were stained with HBFP to demonstrate ischemia. Eleven dogs had venous obstruction, 5 dogs were acute (killed within 24 hours), and 6 dogs were chronic. Sixteen dogs had lymph obstruction, 4 dogs were acute, and 12 dogs were chronic. Twenty dogs had lymph obstruction in addition to venous obstruction, 5 dogs were acute, and 15 dogs were chronic. Nineteen animals served as control animals, 6 dogs were acute, and 13 dogs were chronic. Autopsies excluded all animals with any compromise of the arterial circulation. Large areas of myocardial fibers staining positively with HBFP were seen in acute and chronic experimental dogs from 1 hour to 90 days after operation. No gross or microscopic infarctions were found in the acute or chronic control dogs. Thirty-three per cent of dogs with chronic venous obstruction or chronic lymph obstruction showed gross infarctions without additional microscopic areas of infarction. In dogs with combined venous and lymphatic obstruction, 40 per cent had gross infarctions, whereas 87 per cent had a combination of gross plus microscopically evident infarctions. Thus, interference with the outflow of venous blood and lymph, without interference with the arterial blood supply, can lead to significant myocardial pathology of a type usually associated with a deficit in arterial blood supply. If, as has been postulated, the HBFP stain is specific for ischemic muscle fibers, our results seem to indicate that such a stage of ischemia can persist over a prolonged period of time without progressing to necrosis; or, alternatively, that over the course of time progressively more fibers that are in or near a fibrotic area slowly become ischemic. These findings in dogs provide support for the potential usefulness of myocardial revascularization procedures.