Cardiac sarcoidosis

Article written and reviewed by Dr Luca Moretti

Cardiac sarcoidosis is a granulomatous inflammatory disease capable of involving the myocardium, the conduction system and, less commonly, the pericardium and valves. It may occur in the setting of already established pulmonary or multisystem sarcoidosis, but an apparently isolated phenotype also exists in which the heart is the only clinically apparent organ involved. In the latter scenario, diagnostic certainty is more difficult to achieve and the likelihood of confusing a genetic cardiomyopathy, giant cell myocarditis or a granulomatous infection is greater.

The disease does not behave like a uniform infiltrate; active granulomas and edema may occupy one region, while a nearby area contains mature fibrosis or apparently normal tissue. This heterogeneity evolves over time and explains the limited sensitivity of unguided biopsy. It also explains why clinical risk may sometimes present with atrioventricular block or ventricular tachycardia long before echocardiography shows global cardiomyopathy.

Prevalence depends on the method of investigation and the population; clinically apparent involvement is less common than that detected at autopsy or by systematic imaging, while geographic and ancestral differences suggest genetic and environmental contributions. These data do not justify indiscriminate population screening, but they support structured assessment of patients with extracardiac sarcoidosis and individuals with sentinel cardiac phenotypes.

The 2024 American Heart Association scientific statement interprets the clinical diagnosis as a continuum of probability, recognizing that no single test has absolute sensitivity and specificity. This approach is particularly useful because it separates three different questions: how likely it is that the heart is involved, how much inflammatory activity is still present, and what arrhythmic risk remains within the scar. Confusing these questions leads to inappropriate treatments and devices.

The clinical pathway must answer three questions separately: whether the heart is involved, whether treatable activity is present, and what risk derives from the scar. A patient may have a high diagnostic probability, a negative PET scan and still have high arrhythmic risk because of extensive LGE, or may have metabolic activity with preserved function and no documented arrhythmia. Collapsing these three dimensions into a single label of “active sarcoidosis” weakens decisions that instead require distinct therapeutic targets.

The degree of certainty required depends on the consequence: intensified surveillance may be reasonable at an intermediate probability, whereas years of immunosuppression require a more robust basis. This principle makes it possible to act without waiting for unattainable certainty while preserving the ability to revise the hypothesis when genetic findings, microbiology or new tissue evidence becomes available.

Etiology, Pathogenesis and Pathophysiology

The ultimate cause of sarcoidosis remains incompletely defined; in a genetically predisposed host, one or more environmental or microbial antigens appear to sustain a disproportionate T-cell and macrophage response, with formation of noncaseating granulomas. Variants within the HLA system and other immune pathways influence susceptibility and phenotype, but no genetic test is diagnostic when used in isolation.

A sarcoid granuloma is an organized aggregate of epithelioid macrophages, giant cells and lymphocytes, with necrosis generally limited compared with caseating infections or giant cell myocarditis. Over time it may resolve, persist or be replaced by collagen. The number of granulomas observed in a sample does not necessarily reflect the burden in the entire heart, because distribution is irregular and sampling selects only a minute portion of tissue.

The basal septum is frequently involved, and injury to the atrioventricular node or His bundle produces conduction block. In the ventricular myocardium, edema and necrosis cause electrical instability during the active phase, while fragmented fibrosis creates slow-conduction channels that sustain reentry. This dual pathophysiology allows tachycardia to occur both during inflammatory activity and years after its suppression.

Systolic dysfunction results from myocyte loss, reversible inflammatory depression and remodeling, with possible focal aneurysms and wall thinning. The right ventricle may be directly involved or may deteriorate because of lung disease and pulmonary hypertension, but the two mechanisms require different strategies; a reduction in ejection fraction may be aggravated by nonphysiological pacing or persistent tachyarrhythmias.

Activity and scar are not synonymous; FDG uptake after appropriate metabolic suppression suggests active inflammatory cells, whereas late gadolinium enhancement documents expansion of the extracellular space due mainly to injury and fibrosis. A region may be positive on both modalities, on only one, or may change over time, and this combination influences immunosuppression and prognostic assessment.

The apparently isolated form poses a biological and diagnostic problem; it may represent truly heart-confined disease, extracardiac sarcoidosis below the threshold of detection, or a cardiomyopathy with secondary inflammation. Pathogenic variants in cardiomyopathy genes have been identified in a proportion of patients labeled as having isolated sarcoidosis, so family history and the genetic phenotype should not be overlooked.

The granulomatous differential diagnosis includes tuberculosis, mycoses and foreign bodies; before suppressing immunity, epidemiology, extracardiac imaging, stains, cultures and molecular techniques should reasonably reduce the likelihood of infection. A noncaseating granuloma is not specific to sarcoidosis, just as a negative immunologic test does not by itself exclude tuberculosis.

The lesion may extend inward from the epicardium or occupy the septum deeply, creating substrates that are difficult to reach with biopsy and endocardial ablation. New foci may appear while others subside, and stable global function may conceal a redistribution of risk; segment-by-segment comparison between studies is therefore more informative than the change in ejection fraction alone.

Granulomas and scars alter regional mechanics before dilation develops, with reduced strain and small but arrhythmogenic aneurysms. Right-sided involvement must be distinguished from elevated pulmonary pressure due to respiratory disease, because myocardial activity and pressure overload require different responses; CMR, echocardiography and selected catheterization clarify this physiology.

Clinical Manifestations

Conduction disease is often the initial sign; advanced second-degree or complete atrioventricular block in a person under sixty years of age, without a convincing ischemic, drug-related or degenerative cause, warrants investigation for sarcoidosis and other forms of myocarditis before or at the time of device implantation. PR prolongation or bundle branch block may precede progression and become more meaningful when associated with troponin elevation, LGE or arrhythmias.

Ventricular arrhythmias include premature ventricular complexes, nonsustained tachycardia, monomorphic ventricular tachycardia and ventricular fibrillation. Palpitations and syncope may be mistaken for benign disorders, whereas cardiac arrest may be the first manifestation in a patient with preserved function. Epicardial and intramural scar makes the substrate complex and sometimes inaccessible with a single endocardial procedure.

Heart failure results from left-, right- or biventricular dysfunction and may evolve as a dilated cardiomyopathy. Dyspnea, edema and reduced functional capacity do not distinguish activity from scar; worsening may result from an inflammatory flare, arrhythmia, pacing, fibrotic progression or lung disease. Establishing the mechanism prevents an increase in corticosteroids in the setting of purely hemodynamic congestion.

Chest pain and an acute myocarditis-like phenotype are possible, with elevated troponin and ST-T abnormalities; pericardial effusion is generally small, whereas predominant pericarditis requires consideration of alternatives. Coronary artery disease may coexist and is assessed according to risk, because a nonischemic imaging pattern does not automatically exclude a clinically relevant stenosis.

In patients with extracardiac sarcoidosis, symptoms such as palpitations, syncope and dyspnea warrant investigation, but the absence of symptoms does not guarantee normality. ECG and history form an initial filter, with monitoring and echocardiography added when abnormalities are present; elevated biomarkers increase suspicion, but normal values do not exclude an electrically dangerous scar.

Extracardiac manifestations include hilar and mediastinal lymphadenopathy, interstitial lung disease, skin nodules, uveitis, neuropathy and hepatic or splenic involvement; their presence may provide a lower-risk biopsy site, but does not measure the severity of cardiac disease. Conversely, pulmonary stability does not prove that myocardial inflammation is inactive, because different organs may follow different trajectories.

Pregnancy, athletic activity and other states of increased demand may unmask arrhythmias or failure, but they do not cause sarcoidosis. Individual assessment considers function, rhythm, treatment and devices, avoiding rules based only on the diagnostic label; return to intense exertion requires documented stability and appropriate arrhythmic assessment.

Screening should remain proportionate, because subjecting every asymptomatic patient indiscriminately to repeated PET scans increases radiation exposure, indeterminate findings and uncertain treatment. Symptoms, ECG abnormalities, arrhythmias or dysfunction identify those who benefit most from advanced imaging, while the threshold is lower in high-risk systemic phenotypes. The strategy is adapted to guidelines and resources rather than reduced to an unchanging algorithm.

Syncope may reflect intermittent block, ventricular tachycardia, hypotension or a neurologic cause and requires monitoring proportionate to event frequency. A negative short Holter recording is not reassuring when episodes are rare; prolonged recorders, electrophysiological study and imaging are selected according to the probability and consequences of a missed event.

Investigations and Diagnosis

ECG is used to identify block, QRS fragmentation, nonischemic Q waves and repolarization abnormalities, while Holter monitoring and prolonged monitors quantify premature beats and tachycardias. Echocardiography assesses biventricular function, strain, aneurysms, septal thinning and pulmonary hypertension; none of these tests is sufficiently sensitive to exclude early involvement on its own.

CMR is a cornerstone of diagnosis and prognosis; LGE has a variable noncoronary distribution, often multifocal and septal, while T1 and T2 mapping may support the presence of edema and diffuse injury. The amount and location of LGE are associated with event risk, but do not establish whether inflammation remains responsive to immunosuppression.

FDG-PET requires a low-carbohydrate diet, fasting and local protocols to suppress physiological myocardial glucose uptake. Focal uptake, particularly when discordant with perfusion defects, supports activity; diffuse uptake may reflect ineffective preparation. Whole-body imaging searches for extracardiac organs and provides a reference for follow-up studies performed with a comparable technique.

CMR and PET are complementary rather than competing tests; the former may identify extensive scar without metabolic activity, whereas the latter may show inflammation before substantial fibrotic replacement. Concordance increases confidence, but discordant results must be interpreted in light of prior therapy, image quality, disease phase and alternative diagnoses.

Biopsy of lymph nodes, lung, skin or other accessible sites may demonstrate granulomas and permit cultures. Endomyocardial biopsy provides greater cardiac specificity but limited sensitivity; electroanatomical mapping, CMR and PET may direct sampling toward abnormal regions. When giant cell myocarditis must be excluded in a rapidly deteriorating patient, the value of cardiac tissue increases considerably.

Clinical diagnosis uses criteria from scientific societies that are not perfectly overlapping; it is necessary to state which scheme is being applied and to retain a probabilistic assessment, especially in the isolated phenotype without histology. Suggestive imaging should not halt investigation for infection, neoplasia, arrhythmogenic cardiomyopathy or laminopathy when the history and distribution raise doubts.

Arrhythmic risk assessment proceeds in parallel with diagnosis; sustained arrhythmias, cardiac arrest, syncope, reduced function, LGE extent, the need for pacing and selected inducibility contribute to the decision regarding a defibrillator. PET primarily measures an inflammatory target and does not replace this stratification.

Before treatment, complete blood count, renal and liver function, bone metabolism, latent infections and vaccination status are documented, with screening tailored to the immunosuppressive agent. This preparation should not delay therapy when instability is present, but it prevents predictable complications during chronic treatment; multidisciplinary discussion also defines which indicators will be used to measure response.

An interpretable PET scan requires documented metabolic preparation and joint interpretation of uptake and perfusion; a diffusely positive result due to failed suppression is indeterminate, not evidence of activity, and should not guide either escalation or tapering. Repeating the study with an improved protocol may be more informative than basing immunosuppressive decisions on uncontrolled physiological uptake.

Lymph-node biopsy is preferred when it offers a high yield at lower risk, but an extracardiac finding does not prove that every cardiac abnormality has the same cause. Rapid deterioration, a genetic pattern or a coronary stenosis retain their own diagnostic pathway, and the specificity of cardiac tissue becomes increasingly valuable as the phenotype becomes more aggressive or discordant.

Treatment and Prognosis

Immunosuppression is generally considered in clinically manifest cardiac sarcoidosis when there is evidence of activity, particularly block, arrhythmias or dysfunction associated with inflammation. Corticosteroids are the traditional first-line treatment; initial dose, possible pulse therapy, tapering rate and duration vary because the evidence derives mainly from observational studies. The decision balances ongoing injury, reversibility, comorbidities and infectious risk.

Methotrexate, azathioprine, mycophenolate and other agents are used as steroid-sparing treatments or for relapses, while TNF antagonists may be considered for refractory disease under expert supervision. Before each escalation, it is verified that persistent uptake is not due to inadequate preparation and that new dysfunction does not have a mechanical cause; latent infections and heart failure influence the choice of biologic agents.

Response is assessed through symptoms, rhythm, function, biomarkers and imaging, without requiring a single index to normalize before efficacy is declared. Serial PET is useful when the result changes dosing or maintenance and is performed with comparable protocols; LGE may remain stable because it represents scar and is not, by itself, evidence of treatment failure.

Heart failure receives guideline-directed therapy adapted to blood pressure, renal function and right-sided involvement; cardiac resynchronization may be appropriate in dyssynchrony or a high pacing burden with reduced function. In advanced disease, mechanical circulatory support and transplantation are options; extracardiac sarcoidosis must be characterized but does not automatically constitute a contraindication.

Advanced block requires pacing even if corticosteroids might improve conduction, because recovery is unpredictable; a system with defibrillation capability is often preferred when ventricular risk is significant. After cardiac arrest or sustained tachycardia, secondary prevention is not replaced by suppression of PET activity.

Antiarrhythmic drugs and ablation treat recurrent tachycardias, but control of active inflammation improves substrate stability; mapping may require both endocardial and epicardial access because of the intramural distribution. Recurrence does not necessarily imply technical failure of ablation, because new scars may mature if disease activity persists.

Prognosis is heterogeneous; cardiac arrest, sustained tachycardia, syncope, ventricular dysfunction, right ventricular involvement and extensive LGE increase risk. Early diagnosis and treatment may preserve conduction and function but do not always prevent scarring. Contemporary cohorts have better outcomes than historical autopsy series, although they remain selected populations.

Follow-up is prolonged because activity and arrhythmias may reappear during or after tapering; ECG, rhythm monitoring, echocardiography and toxicity surveillance are scheduled according to phenotype, while CMR and PET address specific questions. The patient should know which symptoms require urgent assessment and should have a single coordinated plan shared among specialists.

Corticosteroid tapering should be slow enough to recognize renewed activity and deliberate enough to limit cumulative toxicity; a mild return of uptake without clinical worsening leads to a different decision than new arrhythmias or block. The minimum effective dose, steroid-sparing agent and measurable targets are redefined at each phase instead of maintaining the initial regimen by inertia.

Toxicity prevention includes bone health, metabolism, blood pressure, ophthalmologic care, vaccinations and infectious prophylaxis tailored to the treatment combination, while steroid-sparing agents require their own liver, bone marrow or renal monitoring. This surveillance also supports efficacy, because abrupt treatment interruption due to a predictable complication exposes the patient to reactivation.

Complications

Sudden death may result from tachycardia, fibrillation or block and is not confined to patients with severely reduced ejection fraction. A limited but strategically located scar may be sufficient; multiparametric stratification and a defibrillator in appropriate patients address this risk without promising absolute protection.

Electrical storm produces repeated shocks, sedation, hemodynamic deterioration and a substantial psychological impact. It is necessary to distinguish inflammatory reactivation, new scar circuits, metabolic disturbances and drug-induced proarrhythmia; immunosuppression, antiarrhythmics, ablation and autonomic modulation are combined according to the dominant mechanism.

Progression toward biventricular failure may continue despite reduced activity when myocardial loss is extensive. Functional regurgitation, pulmonary hypertension and renal dysfunction complicate titration; late referral to a transplant center may reduce options, so advanced evaluation should precede multiorgan failure.

Opportunistic infections, hepatotoxicity, cytopenias, diabetes, osteoporosis and malignancies are complications of therapy and require screening, prophylaxis and monitoring. Fever during immunosuppression should not automatically be attributed to sarcoidosis; the decision to reduce or change an agent considers the immediate risk of cardiac inflammation and the cumulative risk of treatment.

Chronic pacing may worsen dyssynchrony and ventricular function, while multiple leads increase the complexity of future procedures; initial planning considers the likelihood of future defibrillation and resynchronization, venous access and anticipated progression. Recovery of conduction does not guarantee that the device will no longer be necessary for ventricular risk.

An erroneous diagnosis of isolated sarcoidosis may expose a person with genetic cardiomyopathy to years of immunosuppression. Conversely, attributing LGE and block exclusively to genetics may leave treatable inflammation active; periodic reassessment, family history, selected genetic testing and extracardiac investigation protect against both directions of error.

Recurrence in the transplanted heart is possible but does not negate the benefit of transplantation. Granulomas in the graft must be distinguished from rejection and infection through pathology, cultures and clinical context; transplant follow-up incorporates this possibility into surveillance without indiscriminately intensifying immunosuppression.

Quality of life is affected by ICD shocks, corticosteroid effects, diagnostic uncertainty and fear of exertion even when tests appear stable. Personalized cardiac rehabilitation and psychological support help patients resume activity without ignoring risk, whereas vague advice to avoid all exercise promotes deconditioning. The plan defines permitted intensity, warning signs and reassessment intervals, keeping recommendations from the cardiologist, pulmonologist and electrophysiologist consistent.