Cardiac Sarcoidosis: Why It Is Underdiagnosed, How Imaging Finds It, and When Ablation Is Needed

Research-informed explainer — last updated April 12, 2026

Cardiac sarcoidosis causes sudden cardiac death, complete heart block, and ventricular tachycardia in adults who often appear otherwise healthy — and autopsy series suggest it is present in 25–50% of patients who die from systemic sarcoidosis but diagnosed clinically in only 5%. Modern imaging with cardiac MRI and FDG-PET has transformed the detection rate, but awareness remains the primary barrier to earlier diagnosis.

This article draws on research from five cardiologists with expertise in cardiac sarcoidosis and inflammatory heart disease imaging. Manesh Patel, M.D., Chief of Cardiology at Duke University Hospital, is the lead author of a pivotal 2009 study in Circulation demonstrating that cardiac MRI can detect myocardial damage in sarcoidosis when standard testing is negative. Sharmila Dorbala, MD, Professor of Radiology and Director of Nuclear Cardiology at Brigham and Women's Hospital, published a landmark study showing that FDG-PET significantly enhances prognostic assessment in suspected cardiac sarcoidosis. Eric Good, DO, at the University of Michigan Health, published landmark multicenter data on radiofrequency catheter ablation of ventricular tachycardia in cardiac sarcoidosis. Paul Schoenhagen, MD, at Cleveland Clinic, is a cardiac imaging specialist whose work on CT and multimodality imaging informs the differentiation of cardiac sarcoidosis from other infiltrative cardiomyopathies. Paul Cremer, M.D., Associate Professor at Northwestern Memorial Hospital, is an expert in cardiac inflammatory disorders and PET imaging for cardiac disease.

What is cardiac sarcoidosis?

Sarcoidosis is a multisystem granulomatous disease of unknown etiology, characterized by the formation of non-caseating granulomas — dense collections of immune cells — in affected organs. The lungs and lymph nodes are the most commonly affected sites, followed by the skin, eyes, and liver. Cardiac involvement occurs in approximately 25–40% of patients with systemic sarcoidosis at autopsy, though clinical cardiac sarcoidosis is diagnosed in only 5% of all sarcoidosis patients during their lifetime.

The critical difference between clinical and subclinical cardiac sarcoidosis is that even small amounts of granulomatous infiltration of the heart's conduction system can cause life-threatening arrhythmias. Granulomas in the cardiac sarcoidosis tend to concentrate in the ventricular free walls, the basal septum, and the conduction system — precisely the locations where damage is most dangerous.

Why cardiac sarcoidosis is so commonly missed

The diagnosis is challenging for several reasons:

Variable presentation: Cardiac sarcoidosis presents in multiple ways — complete heart block (often in a young adult with no other cardiac history), ventricular tachycardia, systolic dysfunction, or heart failure. Up to 20% of unexplained complete heart block in adults under 55 is caused by cardiac sarcoidosis.

No highly sensitive single test: Endomyocardial biopsy has low sensitivity (25–30%) because granulomas are often patchy and can be missed even with multiple samples. Holter monitoring and 12-lead ECG have limited sensitivity. Standard echocardiography may appear relatively normal early in disease.

Lack of awareness: Because sarcoidosis is considered primarily a lung disease, cardiac workup is often omitted or limited, particularly when pulmonary symptoms are the chief complaint.

How cardiac MRI and FDG-PET changed diagnosis

Two imaging tools have transformed the detection of cardiac sarcoidosis:

Cardiac MRI with late gadolinium enhancement (LGE): Research by Patel and colleagues published in Circulation in 2009 showed that CMR can detect myocardial damage in sarcoidosis even when standard testing — ECG, echocardiogram, and Holter monitoring — are all normal. LGE in cardiac sarcoidosis typically appears as patchy, non-ischemic enhancement in a basal septal distribution, distinct from the subendocardial or transmural pattern seen in coronary artery disease. In the study, CMR detected additional cardiac abnormalities in patients whose standard workup was unremarkable.

FDG-PET (fluorodeoxyglucose positron emission tomography): Research by Dorbala and colleagues published in the Journal of the American College of Cardiology in 2013 evaluated 118 patients with suspected cardiac sarcoidosis and demonstrated that FDG-PET significantly enhances prognostic assessment over CMR alone. Patients with positive FDG-PET — indicating active metabolic inflammation in the myocardium — had significantly higher rates of adverse cardiac events including death and sustained ventricular arrhythmia. PET images areas of active granulomatous inflammation, while CMR detects the resulting fibrosis; combining both modalities provides the most complete picture.

The practical implication: for patients with known systemic sarcoidosis and unexplained cardiac symptoms, or with unexplained complete heart block or ventricular tachycardia, the evaluation should include both cardiac MRI and FDG-PET, not just standard echocardiography.

The HRS 2014 diagnostic criteria

The Heart Rhythm Society 2014 expert consensus statement provides the most widely used diagnostic criteria for cardiac sarcoidosis. Diagnosis requires either:

1. Histological confirmation from cardiac tissue showing non-caseating granulomas without an alternative explanation, OR
2. Probable cardiac sarcoidosis in a patient with histologically proven extracardiac sarcoidosis who also has: one or more of complete heart block, unexplained reduced ejection fraction (<40%), unexplained sustained VT, or Mobitz type II or complete AV block — plus one of: abnormal FDG-PET, abnormal nuclear perfusion scan, or LGE on CMR in a non-ischemic pattern.

For the workup, multimodality imaging recommendations from Schoenhagen and colleagues, including the comprehensive ASE guidelines on pericardial disease and other cardiac conditions, inform how CT and CMR should be integrated with clinical history in evaluating patients with suspected infiltrative cardiomyopathy.

Treatment: steroids, ICD, and ablation

Corticosteroids are the primary anti-inflammatory therapy. Prednisone (typically 0.5 mg/kg/day, tapered over months) is used to suppress active granulomatous inflammation, particularly when there is evidence of active disease on FDG-PET. The evidence base is mostly observational, but corticosteroids appear to reduce granuloma burden, may improve conduction disease, and can improve ejection fraction in patients with steroid-responsive inflammatory cardiomyopathy.

FDG-PET is used both to identify patients likely to respond to steroids (those with active inflammatory uptake) and to monitor treatment response — metabolic activity on PET typically decreases with successful therapy, though LGE from established fibrosis does not reverse.

Implantable cardioverter-defibrillators (ICDs) are recommended in most patients with cardiac sarcoidosis who have sustained ventricular arrhythmias, significant LV dysfunction (EF below 35%), or unexplained syncope. Because sudden death risk exists even in patients with preserved EF, the threshold for ICD implantation in cardiac sarcoidosis is lower than in other cardiomyopathies.

Catheter ablation for ventricular tachycardia: Research by Good and colleagues, published in Heart Rhythm in 2008 from a multicenter registry, examined the role of radiofrequency catheter ablation in 19 patients with cardiac sarcoidosis and ventricular tachycardia. At follow-up, 53% were free from VT recurrence on antiarrhythmic drugs. Importantly, ablation in cardiac sarcoidosis is technically challenging because scars are often epicardial (on the outer surface of the heart), multiple, and irregular — requiring both endocardial and epicardial mapping approaches. The results are less durable than in typical post-infarction VT, reflecting ongoing active inflammation that can generate new arrhythmic substrates. Ablation is typically performed as an adjunct to antiarrhythmic drugs and ICD therapy rather than as a curative strategy.

The diagnostic workup for a patient with unexplained heart block or VT

For a patient under 60 with unexplained complete heart block or sustained ventricular tachycardia and no prior cardiac history, cardiac sarcoidosis should be high on the differential. The workup should include:

1. Chest imaging (CT chest without contrast) to look for lymphadenopathy or interstitial lung disease consistent with sarcoidosis
2. ACE level and serum calcium (elevated in active sarcoidosis, but normal in up to 40%)
3. Ophthalmologic exam (uveitis is common)
4. Cardiac MRI with LGE protocol
5. FDG-PET if available (requires metabolic preparation: low-carbohydrate diet for 24–48 hours before imaging to suppress physiologic myocardial glucose uptake)
6. Consider bronchoscopy or other extracardiac biopsy target if lymphadenopathy is present
7. Endomyocardial biopsy if other methods are non-diagnostic and suspicion remains high

Questions to ask your doctor

• Given my heart block (or ventricular tachycardia), has cardiac sarcoidosis been considered and evaluated with cardiac MRI?
• Should I also have an FDG-PET scan to look for active inflammation?
• If I have systemic sarcoidosis, has my heart been specifically screened?
• If I am on steroids, how is treatment response being monitored — with serial imaging or inflammatory markers?
• Do I need an ICD given my diagnosis, even if my ejection fraction is preserved?
• If I have recurrent VT despite medication, am I a candidate for catheter ablation at a high-volume cardiac sarcoidosis center?

The bottom line

Cardiac sarcoidosis is a life-threatening but frequently missed diagnosis, responsible for a substantial proportion of unexplained heart block and sudden cardiac death in young adults. Cardiac MRI and FDG-PET have dramatically improved detection and prognostic stratification — but awareness must come first. Any patient with unexplained complete heart block, sustained ventricular tachycardia, or known systemic sarcoidosis should be evaluated with dedicated cardiac imaging, and management should be coordinated at centers experienced with this condition.