Jessica M. Mann

Vulnerable Plaque Relation of Characteristics to Degree of Stenosis in Human Coronary Arteries

BACKGROUND The microanatomic features of the atherosclerotic plaque at risk of disruption include a large lipid core, a high macrophage content, and a thin cap. The relation between lipid core size, plaque size, and cap thickness either with each other or with the degree of stenosis has yet to be evaluated in human coronary arteries. METHODS AND RESULTS Atherosclerotic coronary plaques (n = 160) were obtained from 31 subjects who died suddenly of ischemic heart disease. In coronary arteries perfused with formol saline at a pressure of 100 mm Hg, stenosis was measured by comparison of the minimal lumen size at the site of a plaque with that of the lumen in an adjacent normal segment of artery. Plaque size, the size of the lipid core, and the thickness of the cap were measured in histological sections. Lipid core size ranged from 0% to 82% of overall plaque size. Seventeen percent of plaques had a core size of > 50%. Linear regression showed no relation of core size to stenosis (r = .21). Absolute plaque size bore no relation to core size (r = .14). Minimal cap thickness was not related to core size (r = .06). Ten percent of plaques predicted to be angiographically invisible had cores of > 50%. CONCLUSIONS Two major determinants of plaque vulnerability, core size and cap thickness, are not statistically related. Neither of these two factors that confer vulnerability are related to absolute plaque size or to the degree of stenosis.

Identification of alpha- and beta-cardiac myosin heavy chain isoforms as major autoantigens in dilated cardiomyopathy.

BACKGROUND Immunization with cardiac myosin induces experimental autoimmune heart disease in genetically predisposed mice. These mice produce heart-specific autoantibodies, some of which are directed against the cardiac myosin isoform. METHODS AND RESULTS We have reported the presence of circulating heart-specific autoantibodies in 26% of patients with idiopathic dilated cardiomyopathy (DCM) using indirect immunofluorescence. To identify the autoantigen(s) recognized by heart-specific autoantibodies in human disease, we tested, by Western blotting, sera from 26 DCM patients, 14 of whom were cardiac antibody-positive and 12 antibody-negative, as well as sera from 12 patients with cardiac failure from ischemic or valvular heart disease and from 13 normal subjects who were cardiac antibody-negative. Crude myofibrillar proteins and myosin preparations extracted from human atrial or ventricular specimens were used as antigens. Sodium dodecyl sulfate polyacrylamide gel electrophoresis was performed. The proteins were electrophoretically transferred to nitrocellulose sheets. The paper strips were incubated in sera from patients or controls at 1:100 dilution; the reaction was revealed with a peroxidase-labeled second antibody against human immunoglobulin. Twelve of the 14 DCM sera (86%) containing heart-specific antibodies reacted with both the alpha- (atrial specific) and beta- (ventricular and slow skeletal) myosin heavy chain isoforms; none of the 13 normal sera (p = 0.0001) and one of the 24 heart failure-negative control sera (4%, p = 0.0001) contained antibodies against myosin heavy chain. CONCLUSIONS These findings indicate that alpha- and beta-cardiac myosin heavy chain isoforms as in the murine model of autoimmune heart disease are major autoantigens in patients with idiopathic DCM.

Dilated cardiomyopathy is associated with an increase in the type I/type III collagen ratio: A quantitative assessment

OBJECTIVES The aim of this study was to quantify total collagen and the type I/type III collagen ratio and their localization in hearts with dilated cardiomyopathy. BACKGROUND Patients with dilated cardiomyopathy have an increase in intramyocardial fibrillar collagen. Types I and III are the main constituents and have different physical properties that may affect cardiac compliance. METHODS Nineteen hearts with dilated cardiomyopathy were studied (17 cardiac explants, 2 hearts obtained at autopsy) and compared with reference hearts. Total collagen was determined by hydroxyproline analysis. Collagen types I and III were analyzed using the cyanogen bromide method and immunohistochemical analysis followed by microdensitophotometric quantification. Localization of collagen types I and III was established at the light and electron microscopic levels. Immunoelectron microscopy provided information regarding their localization. RESULTS Total collagen and the collagen type I/type III ratio were increased in hearts with dilated cardiomyopathy (p < 0.05). Electron microscopy showed a diffuse increase in collagen fibrils in the endomysium; the perimysium showed an inhomogeneous increase. Collagen fibrils were thicker, and fibrous long-spacing collagen occurred in the endomysium. Immunoelectron microscopic findings confirmed an increase in type I collagen. CONCLUSIONS Hearts with dilated cardiomyopathy have a statistically significant increase in the collagen type I/type III ratio. The changes occur in the endomysium and perimysium, although with differences in distribution. These changes in intramyocardial collagen may be clinically relevant because they may affect cardiac rigidity and, therefore, eventually may render the heart less compliant. Further studies are needed to evaluate at what point in the course of the disease these changes appear.

Evidence from family studies for autoimmunity in dilated cardiomyopathy

Organ-specific antibodies are found in patients with autoimmune disease and their symptom-free relatives many years before clinical onset. Organ-specific cardiac antibodies can be found in patients with dilated cardiomyopathy (DCM) and their relatives, which supports the idea that DCM is an autoimmune disease. We did non-invasive cardiological assessment and antibody screening in 342 symptom-free relatives (170 male, 172 female, mean [SD] age 31 [16] years). 177 relatives were from 33 families with more than 1 affected individual (familial DCM) and 165 relatives from 31 families with only 1 affected member (non-familial DCM). The frequency of cardiac antibodies was higher among relatives of DCM patients than in controls (20% vs 3.5%, p = 0.0001). In 37 (58%) of the families studied, cardiac antibodies were found in the proband and/or in at least 1 family member and were more common in familial than in non-familial DCM (24% vs 15%, p = 0.036). Antibody-positive relatives were younger (26 [15] vs 33 [17] years, p = 0.01) and had a larger mean echocardiographic left ventricular end-systolic dimension (35 [6] vs 32 [6], p = 0.01 mm) and reduced percentage fractional shortening compared with antibody-negative relatives (31 [6] vs 34 [6], p = 0.008). Presence of cardiac-specific autoantibodies in symptom-free DCM relatives provides evidence of autoimmunity in a subset of our patients (58%), including familial and non-familial forms of DCM. These antibodies are associated with mild left ventricular systolic dysfunction on echocardiography and may be early markers for relatives at risk of DCM.

Experimental Model of Left Ventricular Failure

A model of chronic cardiac failure has undergone extensive hemodynamic investigation. Under anesthesia the homonymous and second diagonal coronary arteries of sheep have been ligated. The resulting myocardial infarction caused significant acute hemodynamic impairment (paired two-tailed t tests), mean pulmonary artery pressure increasing from 7.31 +/- 0.94 to 13.80 +/- 1.19 mm Hg (p less than 0.001), pulmonary artery diastolic pressure increasing from 4.94 +/- 1.03 to 11.13 +/- 1.27 mm Hg (p less than 0.001), and directly measured left ventricular end-diastolic pressure increasing from 9.31 +/- 1.52 to 17.42 +/- 1.82 mm Hg (p less than 0.001) after infarction documented with invasive monitoring. There was a hemodynamically significant left ventricular aneurysm (paired two-tailed t tests) in animals studied 3 months later, with increased mean pulmonary artery pressure from 7.20 +/- 1.15 to 13.80 +/- 2.00 mm Hg (p = 0.009), an increase in pulmonary artery diastolic pressure from 4.60 +/- 1.30 to 12.10 +/- 2.06 mm Hg (p = 0.006), and an increase in left ventricular end-diastolic pressure from 11.00 +/- 1.94 mm Hg before infarction to 17.00 +/- 2.69 mm Hg (p = 0.038). We conclude that this is a useful model of chronic left ventricular failure that is reproducible and applicable to investigations of therapeutic options in chronic heart failure.

Myocardial magnesium depletion associated with prolonged hypomagnesemia: A longitudinal study in heart transplant recipients

OBJECTIVES This study was carried out to establish prospectively the incidence and relation of hypomagnesemia and myocardial magnesium depletion after heart transplantation. BACKGROUND No serial in vivo study of the relation of serum with tissue magnesium has been described. Myocardial magnesium depletion is associated with intracellular calcium overload, an increased incidence of cardiac arrhythmia and changes in coronary vasculature similar to those seen in the accelerated atherosclerosis that compromises graft survival after transplantation. METHODS In a prospective study in 19 consecutive patients, serum and myocardial magnesium content were measured serially for 9 months after heart transplantation. Blood cyclosporine was assayed simultaneously. RESULTS The incidence of hypomagnesemia was 100% during the 9-month study period, with lowest levels at 3 months (mean 0.80 vs. 0.64 mmol/liter, p less than 0.002). Myocardial magnesium depletion developed in 94% and was persistent in 55%; the lowest levels occurred at 6 months (mean 33.6 vs. 30.1, mumol/g, p less than 0.04). Hypomagnesemia predated decreases in myocardial magnesium by 2 to 6 weeks. Peak cyclosporine levels correlated positively with the decrease in serum magnesium. Clinical events were rare. CONCLUSIONS This is the first report of serial measurement of tissue magnesium. Persistent hypomagnesemia is invariably accompanied by myocardial magnesium depletion in the transplanted heart. Reciprocal calcium overload and adverse changes in coronary vasculature would be expected from previous studies and merit further investigation. Should the implications of this study extend to the native heart, myocardial magnesium depletion may contribute to the high incidence of fatal arrhythmic events observed in patients with heart failure, who commonly have persistent hypomagnesemia.

Myocyte nuclear area as a measure of left ventricular hypertrophy in transplant patients

Transplanted hearts have been reported to increase in size/weight in the first few months after transplant and to remain stable thereafter. An indirect way of assessing the changes in heart weight is through the changes in the area of the myocyte nucleus (MNA). We studied 20 patients who had undergone orthotopic heart transplantation more than 12 months previously; 10 had become hypertensive, and the remaining 10 were normotensive. Myocardial biopsies taken the first week after transplant and 6, 12, 24, and 52 weeks after transplant were assessed. Myocyte nuclear area was measured in 200 myocytes/biopsy with an image analyzer. Individual measurements showed a wide variation in MNA, with significant overlaps among the different biopsies. Assessment of MNA at one year showed increased MNA in 4 10 patients in the hypertensive group and 5 10 in the normotensive group. The remaining patients showed either no statistically significant changes in MNA or a significant (p < 0.0001) decrease in MNA. The presence of systemic hypertension was not a predictive factor for significant hypertrophy and, in some cases, not even for hypertrophy itself. We conclude that although there is often an increase in MNA of the transplanted heart at one year posttransplant, this increase is not systematic, and isolated morphometric results should be viewed cautiously.