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Cardiac PET — viability, sarcoidosis and endocarditis
FDG is also taken up by healthy myocardium, so every use of it needs metabolic control: for viability, sugar is given to "switch on" living muscle, and for sarcoidosis and infection a high-fat, carbohydrate-free diet is given to "switch off" healthy muscle.
Why it matters in the exam
Viability: in a patient with ischaemic cardiomyopathy and poor function, the question is whether non-contracting muscle is alive. The classic finding is a mismatch: reduced perfusion with preserved FDG uptake — "hibernating" muscle that may improve after revascularisation. A match — reduced perfusion and reduced FDG — is scar. Tl-201 with reinjection is a SPECT alternative. Before viability FDG a glucose load is given, with insulin in diabetics, so that living muscle switches to burning sugar.
Cardiac sarcoidosis: preparation of at least 12–24 hours of a high-fat, low-carbohydrate diet followed by fasting, sometimes with heparin, to suppress physiological uptake. Focal or "focal on diffuse" uptake, especially with a matching perfusion defect, fits active inflammation; homogeneous diffuse uptake usually indicates failed suppression. The study is also used to follow response to steroids, and uptake outside the heart (mediastinal nodes, lungs) should be sought. Cardiac MRI complements PET.
Endocarditis: under the ESC 2023 guidelines, abnormal FDG uptake around a prosthetic valve is a major criterion, as is labelled leucocyte SPECT/CT. Surgery in the last three months may cause non-specific inflammatory uptake, so interpretation must be careful. In native valves the sensitivity of PET is low. PET is also excellent for infection of intracardiac devices (pacemaker, defibrillator, LVAD) and for finding secondary foci (emboli, spondylodiscitis) in persistent bacteraemia.
Key points
- Perfusion–FDG mismatch — hibernating muscle.
- For viability — glucose load; for inflammation — high-fat diet.
- Sarcoidosis — focal uptake with a perfusion defect.
- Prosthetic valve — FDG uptake is a major criterion.
- PET also finds device infection and secondary foci.
Summary table
| Question | Preparation | Positive finding | Meaning |
|---|---|---|---|
| Viability | Glucose load and insulin | Reduced perfusion with preserved FDG | Hibernating muscle — will benefit from revascularisation |
| Viability — match | Glucose load | Reduced perfusion and FDG | Scar |
| Sarcoidosis | High-fat diet and fasting | Focal uptake with perfusion defect | Active inflammation |
| Prosthetic valve endocarditis | High-fat diet and fasting | Uptake around the valve | Major criterion per ESC |
| Intracardiac device infection | High-fat diet and fasting | Uptake along the pocket or leads | Device infection |
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Sources
- Joint SNMMI–ASNC Expert Consensus Document on the Role of FDG PET/CT in Cardiac Sarcoid Detection and Therapy Monitoring, 2017 — Patient preparation and interpretation
- ESC Guidelines for the Management of Endocarditis, 2023 — Imaging criteria including FDG PET/CT and labelled leucocyte SPECT/CT
- ASNC/SNMMI Guideline: PET Myocardial Perfusion and Metabolism Clinical Imaging, 2016 — Viability assessment
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.