Immunohistochemical characterization of fibrin(ogen)-related antigens in human tissues using monoclonal antibodies.

A new approach to study the distribution of fibrin(ogen)-related antigens was investigated using three different monoclonal antibodies (MAbs) and the avidin-biotin complex immunoperoxidase technique. MAb I8C6 recognizes B beta 1-42 peptide and can react with either fibrinogen or fibrin I; MAb T2G1 recognizes B beta 15-42 peptide and detects fibrin II but does not cross-react with fibrinogen; MAb GC4 reacts with Fragments D/DD derived from plasmin degradation of fibrinogen or fibrin but not with intact fibrinogen. The method can be applied to frozen or Bouin's fixed paraffin-embedded tissues obtained at biopsy, surgery, and autopsy. The distribution of the three antigens observed with the three MAbs was compared with that obtained with a polyclonal antiserum to fibrinogen and with the more conventional histochemical stains used in pathology to demonstrate fibrin deposits in tissues (Lendrum and PTAH). The staining observed with the three monoclonals clearly detected three different populations of fibrin(ogen)-related antigen in the tissues examined. The staining with MAb T2G1 specifically detected fibrin II with greater sensitivity than did conventional stains. The results of this study suggest that this method allows the molecular form of fibrin(ogen)-related deposits in tissues to be determined and this information may help to elucidate the role of fibrin in various disease states, such as atherosclerosis and renal disease, and in tumor growth and metastasis.

Identification and distribution of fibrinogen, fibrin, and fibrin(ogen) degradation products in atherosclerosis. Use of monoclonal antibodies.

Samples of normal and atherosclerotic vessels obtained from vascular and cardiothoracic surgery were examined for the distribution of fibrinogen/fibrin I, fibrin II, and fibrin(ogen) degradation products (Fragment D/DD) by using recently characterized monoclonal antibodies that recognize and distinguish the three molecular forms (MAbs 18C6, T2G1, and GC4, respectively) with the ABC-immunoperoxidase technique. In normal aortas, little fibrinogen/fibrin I or fibrin II was present and no fibrin(ogen) degradation products could be detected. In early lesions and in fibrous plaques, fibrinogen/fibrin I and fibrin II were distributed in long threads and surrounding vessel wall cells and macrophages. Fibrin(ogen) degradation products were not seen in early lesions. In fibrous and advanced plaques, fibrinogen/fibrin I, fibrin II, and fibrin(ogen) degradation products were detected in areas of loose connective tissue, in thrombus, and around cholesterol crystals. The results of this study suggest that increased fibrin formation and degradation may be associated with progression of atherosclerotic disease. The observed distribution of the different molecular forms of fibrinogen also suggests the possibility that the cells present in the lesions actively participate in the fibrinogen-to-fibrin transition within the vessel wall.

Biopsy diagnosis of myocarditis.

In closing, we can only note that none of the classification schemes for myocarditis has been perfect for clinicians, pathologists, and researchers alike. The definition and classification protocol offered by the "Dallas" group is based solely on histology, but we urge its use by physicians and other researchers as a means of imposing some standardization on the study of myocarditis. The question of optimum treatment, particularly immunosuppressive therapy, has never been definitively answered, but it is now clear that a large, multicenter randomized trial is the only proper method to search for such an answer. Standard nomenclature is a prerequisite for this study. In the meantime, the clinical correlates and prognostic utility of these histologic categories may be defined; these morphologic groupings will probably be shown to be clinically heterogeneous. In the end, we hope a hybrid clinical-pathologic scheme for the diagnosis and classification of myocarditis will be forged. Such a protocol, ideally, will allow the correlation of structure with function and also reliably predict clinical behavior and response to treatment so that someday we may be able to both counsel and cure persons with myocarditis.

Circus movement in the canine atrium around the tricuspid ring during experimental atrial flutter and during reentry in vitro.

A Y-shaped lesion in the right atrium allows induction of atrial flutter in dogs. We recorded the activation sequence during this tachycardia from 96 endocardial bipolar electrodes using intracavitary electrode arrays during 12 separate episodes in three isolated perfused hearts. In each case a reentrant impulse circulated around the tricuspid valve orifice in either a clockwise or counter-clockwise direction. Cutting the pathway terminated the rhythm and prevented its reinduction. There was no discrete segment of markedly slow conduction in the reentrant circuit. The tachycardia cycle length was decreased by methacholine and increased by lidocaine. Reentry was also induced in atrial tissue around the tricuspid orifice when this structure was isolated and superfused in vitro. Tachycardia cycle lengths varied from 205 to 399 msec, depending on the circumference of the ring and temperature. Induction of tachycardia by premature stimulation depended on differences in the duration of the effective refractory period among parts of the ring. Conduction velocity was relatively uniform and was slower during tachycardias than during pacing at long cycle lengths. Analysis of the response to premature stimuli that reset the tachycardia provided evidence for incomplete recovery of excitability between depolarizations during the tachycardia. Fast-response action potentials were recorded throughout the pathway and up to six to eight cell layers deep. Histologic studies showed the supravalvular lamina, a circumferential band of fibers several cell layers below the endocardial surface, to be continuous around the tricuspid orifice. Propagation through this layer best explains the conduction velocities observed in the intact heart during flutter in this preparation.

Interobserver variability in the pathologic interpretation of endomyocardial biopsy results.

Controversy exists over the role of endomyocardial biopsy in evaluating patients with dilated cardiomyopathy, particularly in detecting myocarditis and in assessing prognosis. Interobserver variability, if high, could explain conflicting reports. To assess this possibility, we submitted biopsy specimens from 16 patients with dilated cardiomyopathy to seven cardiac pathologists. The same slides were independently reviewed by each and assessed for fibrosis, hypertrophy, nuclear changes on a 0 to 3+ scale, mean lymphocyte count per high-power field, and myocarditis. The prevalance of significant fibrosis ranged from 25% to 69%, hypertrophy from 19% to 88%, nuclear changes from 31% to 94%, and abnormal lymphocyte count from 0 to 38%. One or more pathologists diagnosed definite or possible myocarditis in 11 of the 16 patients. Of these 11 patients, three pathologists agreed about three and two pathologists agreed about five. Myocarditis was diagnosed by a single pathologist in three cases. We conclude that interobserver variability is high in interpreting biopsy specimens from patients with dilated cardiomyopathy and that quantitative and standardized methods are needed to increase diagnostic consistency.

Utility of endomyocardial biopsy in the diagnosis of cardiac sarcoidosis.

Cardiac involvement in sarcoidosis can be demonstrated in about 25 percent of autopsied cases, but antemortem diagnosis is uncommon. To evaluate the usefulness of the endomyocardial biopsy in detecting cardiac sarcoid disease, the medical records of ten patients with sarcoidosis who underwent endomyocardial biopsy for routine clinical indications were reviewed. The patients fell into two groups: patients with known sarcoidosis and presumed cardiac involvement (n = 8), and patients in whom the biopsy finding of sarcoid disease was unexpected (n = 2). Four patients in the first group had positive endomyocardial biopsy results (granulomas and/or marked mononuclear cell infiltrate) and were treated with glucocorticoid therapy with improvement in three; the fourth was disabled with lung disease. The diagnoses of three other patients were revised on the basis of the biopsy results; their therapy was tailored accordingly. The remaining patient may represent a false-negative biopsy result, based on clinical criteria. The two patients in the second group presented with symptomatic ventricular tachycardia and restrictive cardiomyopathy respectively, and in neither case was sarcoidosis considered prior to biopsy results. Overall, a change in treatment strategy based on biopsy results occurred in eight of ten cases. Thus, endomyocardial biopsy is useful for the diagnosis of cardiac sarcoidosis; treatment strategies may be affected by biopsy findings; and rarely, endomyocardial biopsy can provide the first clinical evidence of sarcoid disease that is otherwise occult.

Arteriovenous malformation of the bladder presenting as gross hematuria.

Arteriovenous malformation, in which direct communication is present between arterioles and venules, are reflected histologically by abrupt changes in the thickness of the medial and elastin layers of the vessels. Another result of the lack of the interposed capillary bed is abnormal dilation and, often, advanced small vessel disease, which is due to the increased intravascular pressures as well as to the basic defects in the blood vessel walls. The diversion of arterial flow and small vessel disease may lead to ischemia, which is postulated to stimulate proliferation of the vascular channels in these lesions. Hence, they tend to grow slowly with time. The ischemia, increased pressure, and small vessel disease predispose to ulceration and hemorrhage, which is a common mode of presentation for these lesions. Common sites for arteriovenous malformations are the intestine, central nervous system, lungs, and extremities. The lesion has not been reported in the urinary bladder. The present case of massive hematuria was found at autopsy to be due to an arteriovenous malformation of the bladder neck.

Electrophysiologic and anatomic basis for fractionated electrograms recorded from healed myocardial infarcts.

The electrophysiologic and anatomic basis for fractionated electrograms were investigated in superfused epicardial preparations from infarcted canine hearts. Fractionated bipolar electrograms were frequently recorded in preparations from infarcts 2 weeks to 18 months old but only rarely in preparations from 5-day-old infarcts. The fractionated electrograms were not caused by movement artifacts. They were not associated with depressed transmembrane resting or action potentials (which were found in the 5-day-old infarcts), but rather transmembrane potentials recorded in the vicinity of the bipolar electrodes were normal. Despite the normal transmembrane potentials, activation time in regions where fractionated electrograms occurred was prolonged. However, prolonged activation time by itself did not cause fractionation, since fractionated electrograms were not recorded from normal preparations in which conduction was markedly slowed by a superfusate containing 16 mM potassium and epinephrine. Unipolar electrograms recorded with glass microelectrodes (tip size 1 to 5 microns) showed that activation in regions where fractionated electrograms were recorded was inhomogeneous. Prepotentials were found preceding the upstrokes of some action potentials in regions where double potentials were recorded, suggesting the possibility of electrotonic transmission across high resistance or inexcitable gaps, but no electrotonic potentials were seen in regions with multicomponent fractionated electrograms. Fractionated electrograms were recorded in regions where infarct healing caused wide separation of individual myocardial fibers while distorting their orientation. The anatomic changes probably caused slow and inhomogeneous activation.

Monoclonal antibody identification of mononuclear cells in endomyocardial biopsy specimens from a patient with rheumatic carditis.

A 17-year-old woman with rheumatic carditis underwent endomyocardial biopsy both prior to and following treatment with prednisone and aspirin. Frozen sections from the endomyocardial biopsy specimens were studied with monoclonal antibodies by an indirect immunofluorescence technique to define the composition of the inflammatory infiltrate in the myocardium and to determine whether the composition of the infiltrate is distinctive and diagnostically useful. The specimen from the initial biopsy contained a heterogeneous infiltrate composed of T lymphocytes, macrophages, B lymphocytes, and mast cells. T lymphocytes predominated, and the ratio of T-helper to T-cytotoxic/suppressor cells was 2.0. Following treatment the overall cellularity of the infiltrate was diminished, but the infiltrate remained heterogeneous; T cells predominated, and the T-helper to T-cytotoxic/suppressor ratio was reversed, to 0.59. The composition of the inflammatory infiltrate in this case of rheumatic carditis distinguishes it immunologically from other "idiopathic," presumably virus-associated, forms of myocarditis.

Structural and electrophysiological changes in the epicardial border zone of canine myocardial infarcts during infarct healing.

Structural and electrophysiological properties of the epicardial muscle which survives on the surface of transmural infarcts of the canine heart (epicardial border zone) were studied at different times after occlusion of the left anterior coronary artery (LAD). Isolated preparations were superfused in vitro, transmembrane potentials recorded, and impulse propagation mapped. In preparations from subacute infarcts (1 and 5 days), resting potential, action potential amplitude, upstroke velocity, and duration were all significantly reduced. Well-defined directional differences in propagation occurred. Propagation was more rapid in the direction perpendicular to the left anterior coronary artery than in the direction perpendicular to the base of the heart, because of the uniform anisotropic structure of the surviving muscle fibers which were arranged in tightly packed bundles oriented perpendicular to the left anterior coronary artery. The only ultrastructural abnormalities found in these muscle fibers was an accumulation of large amounts of lipid droplets. As the infarcts healed, resting potential, action potential amplitude, and upstroke velocity returned to normal by 2 weeks, although action potential duration decreased further. Lipid droplets had disappeared, and connective tissue had invaded the epicardial border zone, separating the muscle bundles. By 2 months, action potentials were normal, but the muscle fibers were widely separated and disoriented by the connective tissue (parallel bundles no longer were found). In these regions with a nonuniform anisotropic structure, the well-defined directional differences in impulse propagation were lost. However, activation was very slow, perhaps because of diminished connections between cells. The persistence of slow conduction in healed infarcts may contribute to the occurrence of chronic arrhythmias.

Hepatitis B virus and myocarditis.

Myocarditis may be a serious extrahepatic complication of hepatitis. In this fatal case of serologically documented hepatitis B viral hepatitis, acute myocarditis was present, with histologic features consistent with a viral pathogenesis. Hepatitis B surface antigen was demonstrated by immunoperoxidase methods in small intramyocardial vessels, suggesting that hepatitis B virus infected the heart. The resulting inflammatory heart disease may have been caused either directly, by virus infecting the myocardium, or indirectly, by an immune-mediated mechanism.

Mechanisms for atrial arrhythmias associated with cardiomyopathy: a study of feline hearts with primary myocardial disease.

The cellular electrophysiologic and structural characteristics of arrhythmic and non-arrhythmic atria isolated from feline hearts with spontaneously occurring cardiomyopathy were studied. The animals were divided into three groups according to the degree of left atrial enlargement: mild (group I), moderate (group II), and severe (group III). The right atria were of relatively normal size. Microelectrode recordings showed that inexcitable cells were present in both left and right atria of all groups but were most numerous in the left atria of group III animals. Most inexcitable cells had low resting membrane potentials. There was also a significant reduction in resting membrane potentials, maximum rate of phase 0 depolarization, and action potential amplitude of excitable cells in left atria of animals in groups II and III, whereas action potentials of excitable cells in the right atria were normal. Acetylcholine or norepinephrine often restored excitability to cells that originally did not generate action potentials. Norepinephrine also caused slow-response action potentials as well as abnormal automaticity and triggered activity due to delayed afterpotentials. The diseased atria showed marked structural abnormalities, which were most pronounced in group III cats, including large amounts of interstitial fibrosis, cellular hypertrophy and degeneration, and thickened basement membranes. Therefore electrophysiologic abnormalities and concurrent changes in cell structure may be involved in the genesis of atrial tachyarrhythmias caused by cardiomyopathy.