Sarcoidosis is a systemic inflammatory disease that causes abnormal collections of immune cells, known as non-caseating granulomas, to form in various organs. These granulomas represent an exaggerated immune response to an unknown trigger. While sarcoidosis most commonly affects the lungs and lymph nodes, it can manifest in nearly any organ, including the heart.
Cardiac sarcoidosis (CS) is the specific manifestation where these granulomas infiltrate the heart muscle. Cardiac involvement is estimated to occur in up to 25% of patients with systemic sarcoidosis, though the presentation may be silent in many cases. CS is a significant concern because it can lead to life-threatening complications, including severe heart rhythm abnormalities and heart failure.
The Mechanism of Cardiac Sarcoidosis
The pathology begins with an immune system dysfunction where macrophages and T-lymphocytes cluster to form non-caseating granulomas. These nodules represent a chronic inflammatory process and are the hallmark of the disease. The formation of these granulomas within the heart muscle (myocardium) is typically patchy and unevenly distributed.
The granulomas infiltrate and disrupt the heart’s normal tissue structure, particularly affecting the muscular walls and the electrical conduction system. This active inflammatory phase destroys heart muscle cells, which are then replaced by scar tissue (fibrosis). The resulting structural damage impairs the heart’s ability to contract effectively and interferes with the flow of electrical signals.
Infiltration often affects the interventricular septum, which houses the specialized conduction bundles that regulate the heart’s rhythm. Granulomas may also involve the heart valves, though less commonly, leading to functional abnormalities. Progression from active inflammation to chronic, irreversible scarring dictates the long-term functional problems and disease severity.
Recognizing the Signs
The symptoms of cardiac sarcoidosis arise directly from the structural and electrical damage caused by the granulomas and subsequent scarring. The presentation is highly variable, and some individuals may not experience any symptoms, making early detection challenging. When symptoms manifest, they often fall into two primary categories: electrical conduction problems and myocardial dysfunction.
Electrical problems occur when inflammation or scar tissue interrupts the heart’s natural pacemaker signals. Patients may experience palpitations, lightheadedness, or fainting (syncope) due to abnormal heart rhythms (arrhythmias). These can range from a slow heart rate caused by complete heart block to rapid, dangerous rhythms like ventricular tachycardia, which carries a risk of sudden cardiac death.
Myocardial dysfunction results when the heart muscle is weakened or stiffened by inflammation and fibrosis. This damage can lead to symptoms of heart failure, such as shortness of breath, especially with exertion or when lying flat. Patients might also notice swelling in the legs and abdomen from fluid retention, along with persistent fatigue.
Diagnostic Procedures
Confirming the diagnosis of cardiac sarcoidosis is complex because symptoms mimic many other heart conditions, and the granulomas are often scattered throughout the heart. Initial screening includes an electrocardiogram (ECG) to check for conduction abnormalities or arrhythmias. Blood tests may also be performed, but no single laboratory marker is diagnostic.
Advanced cardiac imaging is central to the diagnostic process, with Cardiac Magnetic Resonance Imaging (cMRI) and Positron Emission Tomography (PET) scans playing complementary roles. A cMRI with late gadolinium enhancement (LGE) identifies areas of scarring (fibrosis) within the heart muscle. The presence of LGE is a strong indicator of prior tissue damage and an increased risk of adverse events.
The specialized 18-Fluorodeoxyglucose (FDG) PET scan is important because it detects active inflammation. FDG is a radioactive sugar analog highly taken up by active inflammatory cells, allowing clinicians to distinguish between active, treatable inflammation and old, irreversible scarring. To ensure accuracy, patients undergoing an FDG-PET scan must follow a specific diet to suppress the heart muscle’s normal glucose uptake, which helps isolate inflammatory cell activity.
While the endomyocardial biopsy (EMB) remains the definitive method to confirm granulomas, its sensitivity is low (less than 25%) due to the disease’s patchy distribution. EMB is an invasive procedure, and a negative result does not definitively rule out the diagnosis. Therefore, diagnosis is typically made by combining clinical presentation, evidence of sarcoidosis elsewhere in the body, and characteristic findings from advanced cardiac imaging.
Management and Therapeutic Approaches
The management of cardiac sarcoidosis involves a dual-track strategy: treating the underlying inflammation and managing the resulting heart damage. Immunosuppressive therapy is the primary approach to control the active disease process. Corticosteroids, such as prednisone, are the first-line treatment, started at a moderate-to-high dose to quickly suppress the inflammatory response.
The goal of this therapy is to halt the formation of new granulomas and prevent further scarring of the heart muscle. Once active inflammation is controlled, the steroid dosage is slowly tapered over several months. Second-line immunosuppressive agents, such as methotrexate or azathioprine, are often added to allow for a lower, steroid-sparing maintenance dose.
Managing cardiac complications is equally important, particularly those related to the electrical system. Patients who experience high-grade heart block often require a permanent pacemaker to regulate their heart rhythm. For those at risk of sudden cardiac death due to dangerous ventricular arrhythmias, an Implantable Cardioverter-Defibrillator (ICD) is necessary. The ICD monitors the heart rhythm and delivers an electrical shock to reset the heart if a life-threatening arrhythmia occurs.
Standard heart failure medications are used to treat myocardial dysfunction. These include drugs like beta-blockers, ACE inhibitors, and diuretics, which optimize heart function and manage symptoms like fluid retention. In advanced cases where heart failure is severe and medical therapies are insufficient, a left ventricular assist device (LVAD) may be necessary as a bridge to heart transplantation, the final therapeutic option.