Natural evolution of cardiac function, cardiac pathology and antimyosin scan in a murine myocarditis model

Noninvasive Contrast-Enhanced Ultrasound Molecular Imaging Detects Myocardial Inflammatory Response in Autoimmune Myocarditis

Background—

Cardiac tests for diagnosing myocarditis lack sensitivity or specificity. We hypothesized that contrast-enhanced ultrasound molecular imaging could detect myocardial inflammation and the recruitment of specific cellular subsets of the inflammatory response in murine myocarditis.

Methods and Results—

Microbubbles (MB) bearing antibodies targeting lymphocyte CD4 (MB CD4 ), endothelial P-selectin (MB PSel ), or isotype control antibody (MB Iso ) and MB with a negative electric charge for targeting of leukocytes (MB Lc ) were prepared. Attachment of MB CD4 was validated in vitro using murine spleen CD4+ T cells. Twenty-eight mice were studied after the induction of autoimmune myocarditis by immunization with α-myosin-peptide; 20 mice served as controls. Contrast-enhanced ultrasound molecular imaging of the heart was performed. Left ventricular function was assessed by conventional and deformation echocardiography, and myocarditis severity graded on histology. Animals were grouped into no myocarditis, moderate myocarditis, and severe myocarditis. In vitro, attachment of MB CD4 to CD4+ T cells was significantly greater than of MB Iso . Of the left ventricular ejection fraction or strain and strain rate readouts, only longitudinal strain was significantly different from control animals in severe myocarditis. In contrast, contrast-enhanced ultrasound molecular imaging showed increased signals for all targeted MB versus MB Iso both in moderate and severe myocarditis, and MB CD4 signal correlated with CD4+ T-lymphocyte infiltration in the myocardium.

Conclusions—

Contrast-enhanced ultrasound molecular imaging can detect endothelial inflammation and leukocyte infiltration in myocarditis in the absence of a detectable decline in left ventricular performance by functional imaging. In particular, imaging of CD4+ T cells involved in autoimmune responses could be helpful in diagnosing myocarditis.

Noninvasive imaging in myocarditis

Increased recognition of the role of inflammation in acute and chronic dilated cardiomyopathy has revived an interest in noninvasive imaging for detection of myocarditis. Diagnostic strategies that are based on molecular imaging promise to further advance our understanding and improve diagnostic precision. This article reviews the strengths and limitations of common clinical tests used for the diagnosis of myocarditis, with a focus on the emerging role of cardiovascular magnetic resonance imaging. Novel imaging modalities that are currently in preclinical development are discussed with recommendations for future clinical research.

A new scoring system to predict the efficacy of steroid therapy for patients with active myocarditis--a retrospective study

The efficacy of steroid therapy for active myocarditis is controversial, so a new scoring system was constructed based on 6 clinical parameters: (1) the mode of onset of the disease; (2) complications of immune-related systemic disorders; (3) evidence of viral infection; (4) the population of infiltrating inflammatory cells; (5) the appearance of multinucleated giant cells in endomyocardial biopsy specimens; and (6) the duration of active myocarditis. Points from -2 to +2 were assigned to each parameter and the total score was calculated from the 6 parameters. Twenty-one patients with clinically suspected myocarditis, who had been admitted to hospital from 1987, were retrospectively analyzed by this scoring system. Sixteen patients were treated without corticosteroids at presentation, and 5 patients were treated by conventional methods with adjunctive use of corticosteroids. In 10 patients of the non-steroid group myocarditis improved and their mean score was -4.8 at presentation. In 6 patients of the non-steroid group, myocarditis and cardiac symptoms persisted after initial therapy, and their score at presentation was -0.8. In 2 patients of the steroid group myocarditis improved after initial therapy and their score was +2. In 2 other patients of the steroid group, myocarditis and cardiac symptoms persisted and their score was +3. Another patient of the steroid group died from congestive heart failure and his score was -5 at presentation. In 8 of 9 patients with persistent myocarditis, the secondary phase therapy was challenged. Seven patients were treated with corticosteroids and 6 patients improved. Their score at the secondary phase was +2.5. Overall, non-steroid conventional treatment was successful in patients with the scores from -5 to -4, and steroid therapy succeeded in patients with scores from 0 to +6. Although this is a retrospective study, this scoring system is able to predict the efficacy of steroid therapy in patients with clinically suspected active myocarditis.

Cardiac manifestations of HIV/AIDS: a review of disease spectrum and clinical management

HIV and AIDS involve multiple organ systems. Lungs, brain, skin, gastrointestinal tract, kidneys, and heart are the major organs targeted by the direct effects of HIV infection and the secondary opportunistic complications of AIDS. Although most other organ system involvement has been extensively described in numerous studies and reviews, cardiac abnormalities related to HIV infection have remained less well characterized, partially because their pathogenesis was less clear and their clinical significance was uncertain. Most studies that have described cardiac complications in AIDS patients were postmortem, although some clinical series have been reported. It is now clear that cardiac involvement in AIDS patients is relatively common. Although most such conditions are clinically quiescent, some may have devastating and fatal outcomes. Pericardial effusion and myocarditis are among the most commonly reported abnormalities. Cardiomyopathy, endocarditis, and coronary vasculopathy have also been reported. In this review, we discuss the most common cardiac abnormalities in HIV-infected patients, as well as their clinical significance, clinical presentation, and management.

Natural evolution of antimyosin scan and cardiac function in patients with acute myocarditis

Indium-111 monoclonal antimyosin antibody imaging is a convenient method to diagnose acute myocarditis. The present study examined the natural evolution of a positive antimyosin scan in 10 patients with acute myocarditis, in relation to left ventricular ejection fraction. All patients underwent myosin-specific monoclonal antibody imaging and radionuclide ventriculography; in all patients endomyocardial biopsy was performed. Repeat assessment of left ventricular function and antimyosin uptake was performed 1, 2 and 6 months later. A heart-to-lung ratio was used to quantify antimyosin uptake. Heart-to-lung ratio in patients with myocarditis was 2.12 +/- 0.31, significantly higher than that observed in eight controls (1.35 +/- 0.08, P < 0.001). During follow-up 2.2 repeat scans per patient were performed. Heart-to-lung ratio normalized (< 1.6) within 1 month in four patients, within 2 months in one patient and within 6 months in two patients; three patients continued to have a positive antimyosin uptake at 6 months, suggesting ongoing myocardial necrosis. At the end of follow-up, ejection fraction improved by > 5% in four patients; normalization or persistence of tracer uptake could not predict an improvement of ejection fraction. It is concluded that antimyosin scintigraphy is useful for diagnosing myocarditis in its subacute or chronic stage during which unknown or immune mechanisms may be in operation. An improvement in left ventricular function cannot be predicted on the basis of persistence or not of tracer uptake.

Experimental rat model representing both acute and chronic heart failure related to autoimmune myocarditis

The most important clinical manifestation of myocarditis is congestive heart failure. The precise mechanisms of heart failure during myocarditis have not been elucidated because no animal model that would permit in vivo study of hemodynamics in severe active myocarditis has been available. We monitored hemodynamics and left ventricular function in a rat model of experimental autoimmune myocarditis to determine if this model could be useful for the study of in vivo hemodynamics in severe active myocarditis. Lewis rats were immunized with human cardiac myosin suspended in complete Freund's adjuvant. Baseline hemodynamics were measured using an ultraminiature catheter pressure transducer via the right internal carotid artery, 4 weeks after immunization in one group of rats (acute phase) and 3 months after immunization in another group (chronic phase). Untreated rats served as the control group. Hemodynamic measurements were also obtained after infusion of dobutamine in the acute-phase and chronic-phase groups. The heart weight-to-body weight ratios were significantly higher in both the acute-phase group and the chronic-phase group compared with normal control rats. The baseline left ventricular systolic pressure was significantly lower in the chronic phase group than in the control group. Peak dP/dt and peak -dP/dt were significantly lower in both the acute-phase group and the chronic-phase group compared with the control group. Dobutamine significantly increased left ventricular systolic pressure, peak dP/dt, and peak -dP/dt in the chronic-phase group but caused only minor changes in hemodynamic variables in the acute-phase group. In vivo measurements of hemodynamic variables indicated the presence of left ventricular dysfunction in rats with experimental autoimmune myocarditis. This animal model may be useful for the study of both acute heart failure related to acute myocarditis and chronic heart failure due to diffuse myocardial fibrosis.

Reduced unloaded sarcomere shortening velocity and a shift to a slower myosin isoform in acute murine coxsackievirus myocarditis

We developed a mouse myocardial preparation to study cellular dysfunction in acute coxsackievirus myocarditis. Thin right ventricular papillary muscles from normal mice (n = 8) were compared with muscles from mice 7 days after coxsackievirus infection (n = 7). Sarcomere shortening was studied with laser diffraction (HeNe, lambda = 623.8 nm). A servomotor was used to shorten a muscle until slack early in isometric contraction. Unloaded sarcomere shortening velocity (Vo) was measured at the start of zero force at slack length. Vo was independent of the extent of slack release and was the same as that estimated with an isotonic force-sarcomere shortening velocity relation. Resting muscle stiffness was calculated from shortening perturbations in resting muscles. The histology of some papillary muscles (normal, n = 4; infected, n = 3) was studied. There was no ventricular hypertrophy. Resting sarcomere length (SL) in infected preparations (2.11 +/- 0.07 micron) (mean +/- 1 SD) was the same as in normal preparations (2.11 +/- 0.08 micron). In isometric twitches in normal and infected muscles, total peak force (4.31 +/- 1.07 and 3.77 +/- 1.86 g/mm2, respectively) resting force (0.81 +/- 0.37 and 0.81 +/- 0.35 g/mm2, respectively), and time to peak force (129.5 +/- 20.3 and 125.2 +/- 13.0 milliseconds, respectively) were not significantly different. Vo was 4.14 +/- 0.84 micron/s in normal muscles at an SL of 2.08 +/- 0.09 micron and 1.70 +/- 0.33 micron/s in infected muscles at an SL of 2.06 +/- 0.08 micron. Resting stiffness was the same for normal and infected muscles. There was inflammation but no fibrosis or necrosis. Thus, Vo was depressed early in acute viral myocarditis without hypertrophy, myocyte necrosis, fibrosis, or altered resting stiffness. Pyrophosphate gel electrophoresis showed a shift from predominantly fast to slow myosin isoforms. Apparently, there is remodeling of the contractile apparatus early in acute coxsackievirus myocarditis that is caused either by the direct effects of the virus or the immune response.

Intraventricular conduction abnormalities in patients with clinically suspected myocarditis are associated with myocardial necrosis

Twenty-nine patients with suspected myocarditis, either with or without intraventricular conduction abnormalities, were investigated for degree of myocardial necrosis by antimyosin scintigraphy. Among those 29 patients, 16 had intraventricular conduction abnormalities. Antimyosin scans were analyzed for heart/lung ratios and semiquantitative visual uptake scores (0 to 4+ scale). Of the 16 patients with conduction abnormalities, 15 (94%) demonstrated visual antimyosin uptake versus 7 (54%) of 13 cases without conduction abnormalities (p < 0.03). In addition, the heart/lung ratios and uptake scores were significantly higher in the group with conduction abnormalities than in the group without (1.64 +/- 0.31 vs 1.39 +/- 0.20, p < 0.03; and 2.3 +/- 0.7 vs 1.4 +/- 0.7, p < 0.005; respectively). In conclusion, intraventricular conduction abnormalities in patients with suspected myocarditis were more strongly associated with active and more severe myocardial necrosis as judged by antimyosin imaging than patients with normal electrocardiograms.

Cardiac sarcoplasmic reticulum calcium ATPase, an autoimmune antigen in experimental cardiomyopathy

BACKGROUND

Various myocardial cell surface and intracellular antigens have been associated with autoimmune myocarditis. Since sarcoplasmic calcium overload is a recognized pathobiochemical finding in cardiomyopathy, we reasoned that there might be a causal relation between inhibition of sarcoplasmic calcium exclusion and pathogenesis of the disease and that immunization with sarcoplasmic reticulum calcium ATPase (SR-ATPase) or antibody specific for SR-ATPase, which can interfere with the regulation of the intracellular calcium content and the myocardial contractility, should lead to the development of cardiomyopathy and possibly myocarditis.

METHODS AND RESULTS

Monoclonal antibody 4C11-20.21 (IgM class) specific for canine cardiac SR-ATPase (M(r) approximately 110 kD) was generated by immunization of CAF1/J mice with dog heart sarcoplasmic reticulum. Antibody 4C11-20.21 inhibits 75% of the enzymatic activity of the cardiac SR-ATPase. This antibody also cross-reacts with the higher M(r) subunit of canine skeletal SR-ATPase, but the skeletal muscle SR-ATPase activity is unaffected. This antibody does not cross-react with sarcolemmal calcium ATPase (134 kD). Antibody 4C11-20.21 was used for affinity purification of cardiac muscle SR-ATPase, which did not contain sarcolemmal calcium ATPase antigen. Nine of 11 CAF1/J mice injected with purified canine cardiac SR-ATPase protein demonstrated myocardial lesions: 3 of 4 mice had occasional perivascular and/or interstitial mononuclear cell infiltrates after 3 weeks, 3 of 4 had borderline myocarditis after 6 weeks, and 3 of 3 had focal myocarditis after 12 weeks. No mononuclear infiltrates were seen in any other organ. To identify the independent effect of 4C11-20.21 antibody on cardiac muscle, 2 x 10(6) hybridoma cells producing the antibody were injected intraperitoneally into 12 severe combined immunodeficiency (SCID) mice. Eleven of 12 SCID mice showed variable cardiac myocyte degeneration without cellular infiltration between 8 and 19 days. Three control SCID mice, which received equivalent injections of hybridoma cells producing IgM anti-myosin light chain antibody, did not show any pathological lesions. Immunoperoxidase staining and/or immunoperoxidase transmission electron microscopy for detection of in vivo localization of 4C11-20.21 demonstrated staining of the subsarcolemmal myotubular system and focal staining of immediately adjacent sarcolemma in animals that received either 4C11-20.21 hybridoma cells or purified canine cardiac SR-ATPase antigen but not in controls. Immunofluorescence staining with goat anti-mouse C3 antibody revealed focal deposition of complement in the cardiac myocytes.

CONCLUSIONS

The time-dependent association between immunization with SR-ATPase antigen and the development of myocarditis in mice suggests that cardiac SR-ATPase constitutes one of several autoimmunogens capable of inducing autoimmune myocarditis. Besides antigenic specificity, since antibody to cardiac SR-ATPase also inhibits energy-dependent processes in the myocardium, it is reasonable to associate the pathological evidence of myonecrosis with the interference of calcium regulation, which controls myocardial contractility.

Antimyosin scintigraphy for detection of myocarditis. Scintigraphic follow-up

To examine the value of antimyosin-indium 111 imaging in relation to endomyocardial biopsy in patients with suspected myocarditis, as well as the natural evolution of abnormal findings on the antimyosin scan, 12 patients with suspected myocarditis underwent endomyocardial biopsy and antimyosin scan. The heart-to-lung ratio (H/L) was used to quantify the antimyosin scan. All 12 patients had abnormal results on the scan (H/L, 1.7 to 2.9; mean, 2.1 +/- 0.3); 8 of the 12 patients also had a diagnostic endomyocardial biopsy. In four patients with abnormal findings on antimyosin scan and normal findings on biopsy, the H/L ratio did not differ from eight patients with abnormal findings on antimyosin scan and a diagnostic biopsy; also, the ejection fraction did not differ between the two groups. One patient died, and 8 patients had a repeat antimyosin scan within 2 months after the initial study. The H/L ratio returned to normal in two out of three patients with normal results on biopsy and in three out of five patients with a diagnostic biopsy; the ejection fraction improved by 8 percent or more in one out of three patients with a nondiagnostic biopsy and in two out of five patients with a biopsy diagnostic for myocarditis. We conclude that the antimyosin scan is more frequently diagnostic than biopsy in suspected myocarditis. Patients with abnormal results on antimyosin scan and a nondiagnostic biopsy, as well as those with abnormal results on antimyosin scan and a diagnostic biopsy, tend to return to normal results on scan within 2 months and improve their ejection fraction.

Active myocardial damage without attending inflammatory response in dilated cardiomyopathy

OBJECTIVES

This study aimed to compare indium-111 (111In)-monoclonal antimyosin antibody uptake in patients with dilated cardiomyopathy before heart transplantation with the histologic findings in the explanted hearts.

BACKGROUND

A high prevalence of 111In-monoclonal antimyosin antibody uptake has been described in patients with dilated cardiomyopathy, suggesting the presence of active, ongoing myocyte damage; however, no correlation between monoclonal antimyosin antibodies and histologic findings is available in these patients.

METHODS

A consecutive series of 21 patients with dilated cardiomyopathy awaiting heart transplantation were studied with monoclonal antimyosin antibodies before the operation, and the results were compared with the histologic analysis of the explanted hearts. The interval between monoclonal antimyosin antibody studies and transplantation was 1 to 90 days (mean 58 +/- 31).

RESULTS

Using a semiquantitative method (heart/lung ratio), monoclonal antimyosin antibody uptake was present in 15 (71%) of 21 patients, but active myocarditis in the explanted hearts was detected in only 7. In 11 patients, intense monoclonal antimyosin antibody uptake coexisting with absent myocyte damage or cellular infiltration of explanted hearts was noted. One patient who showed preoperative monoclonal antimyosin antibody uptake underwent transplantation 11 h later, and ex vivo diffuse myocardial antimyosin uptake was detected, but active myocarditis was seen only at cardiectomy in only a small area of the heart; the rest of the myocardium showed no signs of myocyte damage.

CONCLUSIONS

In dilated cardiomyopathy, monoclonal antimyosin antibody uptake cannot be equated with the presence of an inflammatory response detected in the myocardium of the explanted heart.