Sarcoidosis is a systemic inflammatory disorder characterized by non-caseating granulomas, which are abnormal clumps of immune cells. While it most frequently affects the lungs and lymph nodes, it can impact virtually any organ. Cardiac involvement, known as cardiac sarcoidosis, is relatively uncommon, occurring in a minority of patients. Despite its rarity, cardiac sarcoidosis is serious because it can lead to severe and potentially life-threatening complications.
Cardiac Sarcoidosis: The Mechanism of Heart Damage
Damage begins with the infiltration of granulomas into the myocardium, the muscular tissue of the heart wall. These microscopic inflammatory nodules displace and destroy healthy heart cells, leading to infiltrative cardiomyopathy. The location of these granulomas determines the type of cardiac problem that develops.
A frequent site of infiltration is the interventricular septum, the muscular wall separating the left and right ventricles. This septum houses the heart’s electrical wiring, which coordinates the heart’s rhythm. When granulomas form here, they disrupt the conduction pathway, causing an electrical block. This interference results in serious rhythm disturbances, such as heart block.
Widespread inflammation and subsequent cell death lead to the formation of scar tissue, or fibrosis, within the heart muscle. Fibrosis prevents the heart muscle from contracting efficiently, impairing the heart’s ability to pump blood effectively. This structural damage can lead to dilated cardiomyopathy, ultimately progressing to heart failure.
Recognizing the Signs of Cardiac Involvement
Cardiac sarcoidosis often remains silent, meaning a patient may have no noticeable symptoms until the disease is advanced. When symptoms appear, they frequently relate to electrical or structural damage within the heart. Patients may experience palpitations, which are sensations of a rapid, fluttering, or pounding heartbeat, indicating an underlying arrhythmia. Syncope, or fainting, is another sign, often occurring when a fast heart rhythm prevents adequate blood flow to the brain. Unexplained fatigue or an inability to tolerate exercise may also signal cardiac involvement.
Shortness of breath, especially during exertion or when lying flat, can signal that the heart muscle is too weak to efficiently move fluid, leading to heart failure. Chest pain is also a possible symptom, sometimes caused by inflammation of the heart muscle. Since these symptoms are common to many other heart conditions, connecting them to sarcoidosis requires a high degree of suspicion. The presence of sarcoidosis elsewhere in the body should prompt specialized screening for cardiac involvement, even without obvious symptoms.
Diagnostic Tools and Confirmation
Confirming a diagnosis of cardiac sarcoidosis is complex because the disease is patchy, making it difficult to detect, and no single test is definitive. The initial diagnostic workup typically begins with non-invasive screening tools. An electrocardiogram (ECG) checks for conduction abnormalities like heart block or ventricular arrhythmias. An echocardiogram uses ultrasound to assess heart muscle function and identify areas of wall motion abnormality.
Advanced cardiac imaging plays a significant role in establishing the diagnosis. Cardiac Magnetic Resonance Imaging (CMR) is effective at identifying scarring or fibrosis within the heart muscle, often seen as late gadolinium enhancement (LGE). The pattern and location of LGE in the heart, particularly in the basal septum, are highly suggestive of cardiac sarcoidosis. However, CMR alone cannot distinguish between active inflammation and old scarring.
To identify active disease, a Fluorodeoxyglucose Positron Emission Tomography (FDG-PET) scan is utilized. Inflammatory cells, including sarcoid granulomas, have a high metabolic rate and actively take up the radioactive glucose tracer (FDG). By preparing the patient with a specialized diet, the FDG-PET scan pinpoints areas of intense glucose uptake, indicating active, ongoing inflammation that requires treatment. The combination of CMR (showing scar) and FDG-PET (showing active inflammation) is considered the most comprehensive non-invasive approach for diagnosis.
While endomyocardial biopsy (EMB), which involves taking a small tissue sample, is the definitive standard for sarcoidosis, its practical utility is limited. Granulomas are often distributed unevenly and confined to small regions of the heart muscle. This patchy distribution means the biopsy needle can easily miss the affected area, resulting in a false-negative result and a low diagnostic yield. Therefore, diagnosis often relies on a combination of clinical presentation, abnormal electrical findings, and characteristic advanced imaging results.
Managing and Treating Cardiac Sarcoidosis
Management focuses on two main objectives: suppressing the underlying inflammation and treating the resulting damage to the heart’s structure and electrical system. Immunosuppressive therapy is the first line of attack, aiming to halt the inflammatory process before more scar tissue can form. Corticosteroids, such as prednisone, are the primary agents used to achieve this suppression.
Treatment often starts with a moderate-to-high oral dose of prednisone, which is gradually tapered down over several months guided by clinical response and follow-up imaging. Since prolonged, high-dose corticosteroid use has side effects, steroid-sparing agents are often introduced for long-term management. These secondary immunosuppressive medications, such as methotrexate or azathioprine, help maintain disease control while reducing reliance on corticosteroids.
Specialists simultaneously address the electrical and structural complications caused by the disease. For patients at high risk for dangerous ventricular arrhythmias, an Implantable Cardioverter-Defibrillator (ICD) is often necessary. The ICD constantly monitors the heart rhythm and can deliver an electrical shock to restore a normal rhythm if a life-threatening arrhythmia occurs.
If granulomas cause severe slowing of the heart rate or complete heart block, a permanent pacemaker may be implanted to ensure a stable heart rhythm. For patients who have developed heart failure due to muscle damage, standard medical therapies are used to improve heart function. These medications often include ACE inhibitors or beta-blockers, which help reduce strain on the heart and manage fluid retention symptoms.