Sarcoidosis, an inflammatory disease characterized by the formation of tiny clumps of inflammatory cells called granulomas, can affect nearly any organ in the body, most commonly the lungs and lymph nodes. When these granulomas infiltrate the heart tissue, the condition is specifically termed Cardiac Sarcoidosis (CS). Although it is a relatively rare manifestation of the disease, occurring in an estimated 5% to 25% of patients with systemic sarcoidosis, cardiac involvement is serious and can be life-threatening. The presence of active inflammation and resulting scarring within the heart muscle can severely disrupt normal function. The challenge lies in that cardiac sarcoidosis is often initially silent, only presenting with serious symptoms when damage has already occurred.
How Sarcoidosis Affects Heart Tissue
The underlying pathology of cardiac sarcoidosis involves the direct infiltration of the heart muscle, or myocardium, by these immune cell clusters. These granulomas are noncaseating, meaning they lack the central necrosis often seen in other granulomatous diseases, and they represent areas of chronic inflammation. The inflammatory process triggered by these cell clumps damages the surrounding healthy heart muscle cells and the heart’s internal electrical wiring.
The granulomas frequently target the interventricular septum, the wall separating the two main pumping chambers, which is also home to the heart’s electrical conduction system. Infiltration and swelling in this area physically interrupt the pathway for electrical signals that regulate the heartbeat, leading to rhythm disturbances.
Over time, as the active inflammation subsides, the damaged tissue is replaced by non-functional scar tissue, or fibrosis. This fibrosis further weakens the heart muscle, a process that can lead to cardiomyopathy, where the heart becomes enlarged or stiffened. The presence of scattered scar tissue creates an irregular electrical landscape, predisposing the heart to unstable rhythms. The combination of active inflammation and permanent scarring compromises both the electrical stability and the mechanical pumping ability of the organ.
Recognizing Symptoms of Heart Involvement
The clinical manifestations of cardiac sarcoidosis can be grouped into problems with the heart’s electrical system and issues with its mechanical pumping ability. Electrical disturbances are a common presentation, frequently involving the heart’s rhythm and rate. Patients may experience palpitations, lightheadedness, or fainting, which are often related to arrhythmias.
A common finding is heart block, where the electrical signal transmission between the upper and lower chambers is slowed or completely blocked, often requiring a pacemaker. Life-threatening rhythm issues include ventricular tachycardia, a fast, irregular heartbeat originating in the lower chambers. This underscores the severity of the disease.
Mechanical dysfunction primarily presents as heart failure, where the weakened or stiffened heart cannot pump enough blood to meet the body’s needs. Symptoms include shortness of breath, particularly with exertion or when lying flat, and fluid retention leading to swelling in the legs or abdomen. Cardiac sarcoidosis can sometimes be entirely asymptomatic (subclinical), making routine screening important for those with systemic sarcoidosis.
Confirming a Cardiac Sarcoidosis Diagnosis
Diagnosing cardiac sarcoidosis is challenging because its symptoms mimic many other heart conditions and the disease can be distributed in a patchy way throughout the heart. The diagnostic process relies heavily on advanced, non-invasive imaging techniques to visualize the inflammation and scarring within the myocardium.
Cardiac Magnetic Resonance (CMR) imaging with a contrast agent detects areas of myocardial scarring, known as late gadolinium enhancement (LGE). The pattern of this scarring, which is typically patchy and non-ischemic, strongly suggests sarcoidosis, and its extent is associated with a higher risk of ventricular arrhythmias.
Fluorodeoxyglucose Positron Emission Tomography (FDG-PET) helps distinguish between active inflammation and chronic scarring. This test uses a radioactive glucose tracer highly taken up by activated inflammatory cells within the granulomas. A positive FDG-PET scan indicates active disease that is likely to respond to immunosuppressive treatment.
The combined use of CMR (identifying scarring) and FDG-PET (detecting active inflammation) is crucial for guiding therapy. Inflammation requires immunosuppression, while scarring often requires device therapy. While endomyocardial biopsy (EMB) is the gold standard for definitive diagnosis, its sensitivity is low due to the patchy nature of the disease. Long-term monitoring with an electrocardiogram (ECG) and Holter monitors is used to document electrical conduction disorders and arrhythmias.
Management and Treatment Options
Treatment for cardiac sarcoidosis is multifaceted, focusing on both suppressing the underlying inflammation and managing the resulting cardiac complications. Immunosuppressive therapy is the first line of defense against active disease, with the goal of reducing granuloma formation and preventing further heart damage. Corticosteroids, such as prednisone, are the mainstay of this treatment because of their potent anti-inflammatory properties.
The typical starting dose of a corticosteroid is often high (sometimes 40 to 60 milligrams daily), which is gradually tapered over a period of months as imaging confirms the inflammation is receding. For patients who cannot tolerate the side effects of long-term steroids or whose disease is not fully controlled, second-line immunosuppressive agents may be introduced. These steroid-sparing medications include drugs like methotrexate, azathioprine, or mycophenolate mofetil.
Device therapy is frequently required to manage the electrical complications caused by permanent scarring. Patients who develop high-grade heart block often need a permanent pacemaker to ensure a stable heart rate. For individuals at high risk for dangerous ventricular arrhythmias, an Implantable Cardioverter-Defibrillator (ICD) is recommended. The ICD continuously monitors the heart rhythm and delivers an electrical shock to reset the heart if a life-threatening rhythm is detected.