Antimyosin antibody imaging in clinical myocarditis and cardiomyopathy: principle and application

Recognition and Initial Management of Fulminant Myocarditis: A Scientific Statement From the American Heart Association

Fulminant myocarditis (FM) is an uncommon syndrome characterized by sudden and severe diffuse cardiac inflammation often leading to death resulting from cardiogenic shock, ventricular arrhythmias, or multiorgan system failure. Historically, FM was almost exclusively diagnosed at autopsy. By definition, all patients with FM will need some form of inotropic or mechanical circulatory support to maintain end-organ perfusion until transplantation or recovery. Specific subtypes of FM may respond to immunomodulatory therapy in addition to guideline-directed medical care. Despite the increasing availability of circulatory support, orthotopic heart transplantation, and disease-specific treatments, patients with FM experience significant morbidity and mortality as a result of a delay in diagnosis and initiation of circulatory support and lack of appropriately trained specialists to manage the condition. This scientific statement outlines the resources necessary to manage the spectrum of FM, including extracorporeal life support, percutaneous and durable ventricular assist devices, transplantation capabilities, and specialists in advanced heart failure, cardiothoracic surgery, cardiac pathology, immunology, and infectious disease. Education of frontline providers who are most likely to encounter FM first is essential to increase timely access to appropriately resourced facilities, to prevent multiorgan system failure, and to tailor disease-specific therapy as early as possible in the disease process.

Indium-111 monoclonal antimyosin cardiac scintigraphy in suspected acute myocarditis: evolution and diagnostic impact

BACKGROUND

This study examined the evolution of the heart to lung (H/L) ratio of monoclonal antimyosin antibody (MAA) uptake in patients with suspected acute myocarditis (AM) and its time-dependent diagnostic value in conjunction with echocardiographic findings.

METHODS

The study included 20 patients with a short history (<4 months) of heart failure symptoms and normal coronary arteries. All patients underwent cardiac antimyosin scintigraphy, echocardiography, right-heart catheterization and endomyocardial biopsy. Patients who survived beyond 1 year were reevaluated with a cardiac antimyosin scintigraphy and an echocardiographic study.

RESULTS

Endomyocardial biopsy in 8/20 patients revealed findings compatible with the diagnosis of idiopathic dilated cardiomyopathy (group I) and in the remaining 12/20 was diagnostic of AM (group II). At baseline evaluation of the antimyosin H/L ratio uptake was similar in groups I and II, at 1.95+/-0.19 and 2.16+/-0.51, respectively (P=0.222), while the left ventricular end diastolic diameter (LVEDd) was significantly higher in group I (68+/-12 mm) than in group II (56+/-11 mm, P=0.041). In these patients an initial positive MAA scintigraphy (H/L ratio>1.55) associated with an LVEDd<or=62 mm was diagnostic of AM with a sensitivity of 67%, a specificity of 63% and a positive predictive value of 65%. Upon restudy, the H/L ratio of MAA uptake was significantly decreased in both groups, reaching almost identical levels. No difference was found in the LVEDd between the two groups. The positivity of cardiac antimyosin scintigraphy in conjunction with an LVEDd<or=62 mm had a sensitivity of 45% and a specificity of 88% for the diagnosis of myocarditis.

CONCLUSIONS

In patients with suspected AM a positive antimyosin scintigraphy accompanied by a non-dilated left ventricle is highly suggestive of AM, both at the early phase and 1 year after disease onset.

Pathophysiology of viral myocarditis: the role of humoral immune response

The pathophysiology of viral myocarditis is still a matter of debate. Humoral autoimmunity in postviral heart disease remains an attractive but complex hypothesis. Antigenic mimicry with or without cytolytic antibody properties has been shown to play a role in the immunopathogenesis of myocarditis with respect to sarcolemmal/myolemmal epitopes (including the beta-receptor), myosin and some mitochondrial proteins including the antinucleotide translocator (ANT)-carrier and dihydrolipoamid dehydrogenase. Today, refined two-dimensional Western blots are able to identify receptors and enzymes that are target of a humoral immune response or the consequence of an "immunization process." A humoral immune response to an invading agent will most likely lead to immunodestruction first. After conversion to IgG, the continuing antibody response may indicate the healing or healed process and last for many years or life-long. This paper reviews our present knowledge on the humoral immune response in myocarditis and its interplay with the viral agents and the other components of the immune system.