Acute hemodynamic and coronary circulatory effects of experimental autoimmune myocarditis

Reversible impairment of coronary flow reserve in acute myocarditis

OBJECTIVE

Acute myocarditis is accompanied by an impaired coronary microcirculation. These microcirculatory disturbances are not well defined, and data are derived from complex invasive measurements. Therefore, this study aimed to evaluate the inflammation-induced microcirculatory dysfunction including its reversibility and association with markers of inflammation severity (extent of LGE on CMR imaging and laboratory markers of myocardial necrosis) using the noninvasive technique of echocardiographic CFR measurement.

METHODS

Patients (n = 14) with clinically suspected acute myocarditis in the absence of coronary artery disease were prospectively enrolled, and echocardiographic CFR was determined by measuring peak diastolic coronary blood flow velocity at rest (PDV1) and under adenosine-induced hyperemia (PDV2) at baseline and 3-month follow-up.

RESULTS

Eight of 14 (57.1%) patients showed an impaired baseline CFR (PDV2/PDV1 < 2). These patients were characterized by higher levels of cardiac troponin T (0.55 ± 0.39 vs 0.18 ± 0.08; P = 0.008) and larger areas of LGE on CMR. At 3-month follow-up, CFR was normal in all patients.

CONCLUSION

A reversibly impaired coronary microcirculation is a frequent finding in acute myocarditis and is associated with markers of inflammation severity. Echocardiographic CFR measurement represents a feasible and safe method for its assessment.

Increases in circulating T lymphocytes expressing HLA-DR and CD40 ligand in patients with dilated cardiomyopathy

Inflammatory and immunological mechanisms are implicated in the development of idiopathic dilated cardiomyopathy (DCM). Since activated T lymphocytes express surface HLA-DR antigens, an increased level of these cells in the circulation could indicated an ongoing immune response. While the role of activated T lymphocytes in experimental myocarditis has been elucidated, the contribution of T lymphocyte activation in clinical DCM remains unclear. We therefore examined the role of T-cell activation in peripheral blood samples obtained from 10 patients with DCM (mean age, 49 +/- 12 years) and from 10 age-matched healthy controls. Citrated whole blood was mixed with fluorescein isothiocyanate- or phycoerythrin-conjugated specific monoclonal antibodies and analyzed using a fluorescence-activated cell sorter (FACS). The ratio (%) of histocompatibility leukocyte antigen (HLA)-DR positive cells in the FACS gated lymphocyte population was significantly higher in DCM patients than in controls (7.9% +/- 5.3% vs 2.0% +/- 0.9%; P < 0.01). The expression of CD40L on T cells determined as mean fluorescence intensity (MFI) was also significantly higher in DCM patients than in controls (3.6 +/- 2.1 vs 1.8 +/- 0.4 MFI; P < 0.05). Furthermore, the ratios of T cells expressing HLA-DR and serum brain natriuretic peptide (BNP) levels closely correlated (P = 0.0008). We showed that HLA-DR on peripheral T cells significantly correlated with serum BNP levels and that high CD40L expression on T cells was concomitant with increased BNP levels (P < 0.05). Therefore the magnitude of T-cell expression, such as increased expression of HLA-DR and CD40L, contributes to myocardial dysfunction in DCM.

Cardioprotective effects of recombinant human erythropoietin in rats with experimental autoimmune myocarditis

Erythropoietin (EPO) has been known to have cytoprotective effects on several types of tissues, presumably through modulation of apoptosis and inflammation. The effect of EPO on myocardial inflammation, however, has not yet been clarified. We investigated the cardioprotective effects of EPO in rats with experimental autoimmune myocarditis (EAM). Seven-week-old Lewis rats immunized with cardiac myosin were treated either with EPO or vehicle and were examined on day 22. EPO attenuated the functional and histological severity of EAM along with suppression of mRNAs of tumor necrosis factor (TNF)-alpha and interleukin (IL)-6 in the hearts as well as a reduction of apoptotic cardiomyocytes. The EPO receptor (EPO-R) was upregulated in the myocardium of EAM compared with that of healthy rats. These results may suggest that EPO ameliorated the progression of EAM by modulating myocardial inflammation and apoptosis.

In vivo electron paramagnetic resonance oximetry with particulate materials

Electron paramagnetic resonance (EPR) methods can be used to study tissue pO(2) (PtO(2)) in anesthetized or awake animals (EPR oximetry). The method takes advantage of the fact that some paramagnetic materials have an EPR linewidth that is sensitive to the pO(2) in which the material is located. This article provides an overview of the method of EPR oximetry using implanted particulate materials as the sensors of pO(2). Characteristics of these materials are described to help the reader understand the factors involved in choosing the optimum particulate material. Examples of biological studies are included that show how EPR oximetry may be used on both awake and anesthetized animals.