Sarcoidosis is a systemic inflammatory disease of unknown cause that involves an abnormal immune response, leading to the formation of small clusters of inflammatory cells called granulomas in one or more organs. When this condition specifically affects the heart, it is known as cardiac sarcoidosis (CS). CS is a relatively rare manifestation, but it is serious due to its potential to cause life-threatening heart rhythm problems, heart failure, and sudden death. Because symptoms can be vague or entirely absent, early diagnosis and treatment are important to prevent irreversible damage to the heart muscle and electrical system.
The Formation of Granulomas in the Heart
The underlying process involves the proliferation of granulomas within the heart muscle (myocardium) and other structures. A granuloma is a dense collection of immune cells, primarily macrophages and lymphocytes. While the exact trigger remains unclear, this formation is thought to be an exaggerated cellular immune response to an unknown antigen in a genetically susceptible individual.
These inflammatory clusters cause direct damage by physically disrupting the surrounding heart tissue. The granulomas can develop in a patchy, multifocal pattern throughout the heart, but they frequently affect the interventricular septum and the free wall of the left ventricle. Over time, the active inflammation from the granulomas can resolve, but it often leaves behind permanent, non-contractile scar tissue, a process called fibrosis.
The location of this scarring determines the functional consequence for the heart. When granulomas infiltrate the heart’s conduction system, it can cause blockages in the signal pathway. Scarring in the main pumping muscle of the ventricles leads to a weakened heart muscle, known as cardiomyopathy, which impairs the heart’s ability to pump blood efficiently and results in heart failure.
Recognizing the Signs of Cardiac Involvement
The clinical signs of cardiac sarcoidosis are highly variable and often mimic those of other common heart conditions. In some individuals, the disease is entirely asymptomatic and only discovered incidentally during testing for other conditions. For those who do experience symptoms, they typically fall into two major categories: electrical disturbances or muscle weakness.
Arrhythmias, or irregular heartbeats, are a frequent presentation, manifesting as palpitations, dizziness, or fainting. The infiltration of the heart’s electrical wiring can cause various degrees of heart block, slowing the heart rate, which may require a pacemaker. More dangerously, scarring in the ventricular muscle creates an environment where disorganized electrical signals can rapidly cycle, leading to life-threatening ventricular tachycardia.
Symptoms related to heart muscle weakness often present as heart failure. This is experienced as shortness of breath, particularly during physical activity or when lying flat, and can be accompanied by persistent fatigue. Fluid retention may cause swelling, or edema, in the legs, ankles, or abdomen. Sudden cardiac death is the most devastating complication, often caused by an unmanaged ventricular arrhythmia.
Advanced Diagnostic Procedures
Diagnosing cardiac sarcoidosis is difficult because the symptoms are non-specific and the granulomas are often distributed unevenly throughout the heart. Traditional tests like an electrocardiogram (ECG) or echocardiogram often indicate a problem but cannot provide a definitive diagnosis. Therefore, specialists rely heavily on advanced, non-invasive imaging to visualize the inflammatory process and resulting damage.
Cardiac Magnetic Resonance Imaging (cMRI) is used to detect areas of scarring and inflammation within the heart muscle. The use of a contrast agent, LGE, highlights the non-ischemic pattern of fibrosis characteristic of sarcoidosis, often found in the mid-myocardium or sub-epicardium. The presence of LGE is a significant prognostic indicator.
Positron Emission Tomography (PET) scanning using FDG is the primary tool for identifying active inflammation. Actively inflamed sarcoid lesions consume high amounts of glucose, causing the tracer to “light up” on the scan. Combining cMRI findings of scarring with FDG-PET findings of active inflammation provides a comprehensive picture of both chronic damage and acute disease activity. While endomyocardial biopsy offers a definitive diagnosis by identifying the characteristic non-caseating granulomas, its sensitivity is low due to the patchy nature of the disease.
Treatment Strategies and Long-Term Management
The management of cardiac sarcoidosis is a dual-pronged approach focused on suppressing inflammation and managing the resulting structural and electrical damage to the heart. Corticosteroids, such as prednisone, are the first-line treatment for active cardiac inflammation and are typically started at a high dose.
Corticosteroid therapy can help resolve heart block and improve the heart’s pumping ability, particularly when initiated early in the disease course. For patients who do not tolerate the side effects of high-dose steroids, steroid-sparing immunosuppressive agents are often introduced. These agents include drugs like methotrexate or azathioprine.
Managing the consequences of heart damage often requires device therapy, even if the inflammation is successfully controlled. Patients with significant heart block or a history of fainting may require a permanent pacemaker to regulate their heart rhythm. Individuals at high risk for sudden cardiac death are candidates for an implantable cardioverter-defibrillator (ICD), which delivers a life-saving electrical shock if a dangerous rhythm is detected. Standard heart failure medications, such as beta-blockers and ACE inhibitors, are also used alongside immunosuppression to optimize the heart’s function and manage fluid retention.