The prevalence of sarcoidosis is difficult to ascertain, because many patients are asymptomatic, and the clinical symptoms and histologic findings are nonspecific. In the United States, the overall prevalence of sarcoidosis is estimated at 10 to 40/100,000 persons with an annual incidence of 40/100,000 in blacks compared to 5 to 11/100,000 in whites.^1,2,3 Outside the United States, the highest rate of occurrence is reported in Scandinavia, especially Finland and Sweden (yearly incidence of 5 to 40/100,000 people, prevalence of 64/100,000 population).^1,2 There is a female predominance, especially among African Americans, among whom there is a 2:1 female-to-male ratio.

Cardiac involvement in sarcoidosis occurs in 20% to 30% of patients in autopsy studies, although only 5% of patients with sarcoidosis have clinical manifestations of cardiac disease.³

The etiology of sarcoidosis is unknown. It is presumed to be an immunologic disorder involving acquired cellular immunity directed against an unknown antigen or antigens and possibly environmental factors in predisposed individuals. A number of infectious organisms, including Mycobacteria, Propionibacteria, Borrelia, Rickettsia, and herpes virus have been implicated.^1,2,3 Although nucleotide sequences specific for several organisms have been identified in sarcoid granulomas, the only cultured bacterium has been Propionibacterium acnes, at a higher frequency and concentration than in nonsarcoid lymph nodes.^4,5 A subset of patients demonstrates T- and B-cell responses to mycobacterial antigens.⁶ Environmental factors such as pollen, pica, fireplaces, and mold are epidemiologically associated with systemic sarcoidosis.^7,8,9

Cardiac involvement by sarcoid granulomas was reported as early as 1929,¹⁰ and there have been several subsequent autopsy series.^{11,12,13,14,15,16} Although cardiac involvement is generally around 30% in autopsy series,¹¹ it occurs at a higher rate in Asians, especially Japanese, in whom cardiac manifestations account for as many as 85% of deaths.^13,14,17

There are various clinical manifestations of cardiac sarcoid, including chest pain, palpitations, dyspnea, syncope, conduction abnormalities, ventricular or supraventricular arrhythmias, and heart failure. Conduction abnormalities vary from isolated bundle branch block to complete heart block, which can be detected in 23% to 30% of patients with cardiac sarcoid. There is a poor correlation between cardiac symptoms and extent of cardiac involvement, underscoring the need for better imaging techniques for diagnosing cardiac disease.¹¹

In up to two-thirds of patients with biopsy-confirmed cardiac sarcoidosis, clinical symptoms are limited to the heart.¹⁸

The incidence of sudden cardiac death from sarcoid-induced arrhythmia ranges from 12% to 65% and is associated with extensive myocardial involvement at autopsy.^11,19 Most sudden deaths occur in patients without previously identified cardiac involvement.^{11,15,19,20,21,22} Predictors of sudden death in patients with a clinical diagnosis are similar to other clinical presentations of heart failure and include ventricular arrhythmias, increased left ventricular diastolic diameter, and New York Heart Association functional class.^1,2,3