Clinical meaning
Cardiac sarcoidosis (CS) is a potentially life-threatening manifestation of systemic sarcoidosis, a multisystem inflammatory disease of unknown etiology characterized by the formation of non-caseating granulomas in affected organs. Sarcoidosis has a worldwide distribution with highest incidence in Northern European and African American populations. While pulmonary involvement is the most common manifestation of sarcoidosis (present in >90% of patients), cardiac involvement is clinically evident in approximately 5-10% of sarcoidosis patients during life, though autopsy studies reveal subclinical cardiac granulomas in 20-30% of sarcoidosis patients, suggesting significant underdiagnosis. Cardiac sarcoidosis is responsible for 13-25% of sarcoidosis-related deaths and is the leading cause of death from sarcoidosis in Japan. The pathogenesis of sarcoidosis involves an exaggerated CD4+ T helper cell (Th1) immune response to an unidentified antigen (suspected triggers include Mycobacterium tuberculosis-related antigens, Propionibacterium acnes, and environmental exposures such as insecticides, mold, and beryllium). The activated Th1 cells accumulate at sites of disease activity and produce interferon-gamma (IFN-gamma), interleukin-2 (IL-2), and tumor necrosis factor-alpha (TNF-alpha), which recruit and activate macrophages. These macrophages differentiate into epithelioid cells and multinucleated giant cells, forming the characteristic compact, non-caseating granulomas. Unlike tuberculosis granulomas (which characteristically show central caseous necrosis), sarcoid granulomas are tightly formed collections of epithelioid cells surrounded by a rim of CD4+ lymphocytes and fibroblasts, WITHOUT central necrosis. In the heart, these granulomas can infiltrate any cardiac structure but show predilection for the basal septum, left ventricular free wall, papillary muscles, and the conduction system. The cardiac pathology progresses through three phases. The active inflammatory phase features non-caseating granulomas with surrounding lymphocytic infiltration and myocyte damage. Granulomas within the conduction system (AV node, His bundle, bundle branches) cause conduction abnormalities including AV block (the most common clinical presentation of CS, occurring in 26-67% of patients), bundle branch blocks, and fascicular blocks. Complete heart block in a young patient (<55 years) should always prompt evaluation for cardiac sarcoidosis. The myocardial inflammation phase produces regional wall motion abnormalities (from inflammatory edema and direct myocyte destruction by granulomas), myocardial edema, and may present as acute myocarditis with chest pain, elevated troponin, and heart failure. The fibrotic phase represents the end-stage: granulomas resolve and are replaced by dense fibrotic scar tissue, producing fixed wall motion abnormalities, ventricular thinning, aneurysm formation (particularly in the basal septum and lateral wall), and substrate for re-entrant ventricular arrhythmias. Ventricular tachycardia (VT) is the second most common presentation of CS (occurring in 23-36% of patients) and carries significant sudden cardiac death risk. The granuloma-induced scarring creates electrically heterogeneous zones where islands of viable myocardium are interspersed with fibrotic tissue, providing the anatomical substrate for re-entrant circuits that generate sustained VT. Sudden cardiac death from ventricular arrhythmias accounts for 25-65% of deaths from cardiac sarcoidosis. The third major presentation is heart failure (25-75% of CS patients), resulting from progressive myocardial destruction and replacement by non-contractile granulomatous tissue and fibrosis, producing a dilated cardiomyopathy phenotype with reduced ejection fraction. The clinical challenge of cardiac sarcoidosis lies in its diagnosis, as it can present without prior pulmonary sarcoidosis (isolated cardiac sarcoidosis in approximately 25% of cases), making the diagnosis difficult to establish without a high index of suspicion. Diagnosis relies on a combination of clinical criteria, imaging, and occasionally endomyocardial biopsy. Cardiac MRI (CMR) is the most valuable imaging tool, demonstrating myocardial edema on T2-weighted sequences (active inflammation), and patchy, multifocal late gadolinium enhancement (LGE) in a non-coronary distribution (the mid-wall and epicardial enhancement pattern distinguishes sarcoidosis from ischemic scar, which is subendocardial). FDG-PET scanning (after prolonged fasting or a high-fat/low-carbohydrate diet to suppress normal myocardial glucose uptake) demonstrates focal areas of increased glucose metabolism in active granulomatous inflammation. Endomyocardial biopsy has low sensitivity (approximately 20-30%) because granulomas are patchy and the biopsy may miss affected areas, but when positive (demonstrating non-caseating granulomas) it is diagnostic. The Japanese Ministry of Health criteria and the Heart Rhythm Society expert consensus statement provide standardized diagnostic frameworks. Treatment of cardiac sarcoidosis aims to suppress the granulomatous inflammation and prevent arrhythmic death. Corticosteroids (prednisone 40-60 mg daily, tapered over 6-12 months) are the first-line therapy for active myocardial inflammation. Steroid-sparing immunosuppressive agents (methotrexate, azathioprine, mycophenolate mofetil) are used for steroid-dependent disease or steroid intolerance. Implantable cardioverter-defibrillator (ICD) placement is recommended for patients with sustained VT, hemodynamically significant VT, or LVEF <35% due to cardiac sarcoidosis, given the high sudden cardiac death risk. Permanent pacemaker placement may be needed for advanced AV block. The nurse plays a critical role in monitoring cardiac rhythm, assessing for heart failure progression, managing immunosuppressive therapy, and educating patients about arrhythmia awareness and when to seek emergency care.