Clinical Case Study•Cardiac PET/CT

A Non-Responder with Subsequent Triple-Vessel CAD: Is 24 Hours of Caffeine Withdrawal Enough?

Ronald Sher, MD  ·  Cory Kress, CNMT  ·  Rosemary Englebach, CNMTClinical Associates — Reisterstown, Maryland

Rubidium-82 PET/CTVasodilator non-responseGlobal MBFR 1.113-vessel CAD → CABG

The bottom lineA pre-operative PET study showed normal perfusion but essentially no increase in blood flow after regadenoson — an inconclusive result, not a negative one. Caffeine had been withheld for 24 hours per protocol. Repeating the study after 48 hours off caffeine unmasked a reversible inferolateral defect, and catheterization revealed three-vessel disease referred for bypass surgery.

Case history

  • Elderly female patient with known CAD: myocardial infarction and PCI in 2004
  • Catheterization in 2011 showed no significant residual disease
  • Reason for study: pre-operative evaluation ahead of mastectomy
  • Given a mildly abnormal SPECT several years prior and limited exercise ability, rest/stress PET with myocardial blood flow was ordered

PET protocol

  • Stress agent: regadenoson for both studies; camera GE Discovery NXi, net retention model
  • Study #1 (caffeine withheld 24 hours): 55.1 mCi rest, 55.0 mCi stress; heart rate 56 to 65 BPM; blood pressure 165/72 to 193/77
  • Study #2 (caffeine withheld 48 hours): heart rate 66 to 88 BPM; blood pressure 130/60 to 216/83
  • No stress symptoms on either study; ECG showed non-specific changes both times
  • Quality control good on both studies: good image quality, no misregistration, good blood-flow QC

Myocardial blood flow reserve — repeat study

Values from study #2, after 48 hours off caffeine. On study #1 the global reserve was 1.09 with no meaningful rise in stress flow.

1.30LAD

0.85LCx

0.98RCA

1.11Global

Interpretation and outcome

Study #1 showed normal perfusion with a TID of 1.11 and no change in ejection fraction between rest and stress. Resting flow was normal and uniform, but stress flow did not rise, giving a global reserve of 1.09 — a pattern consistent with non-response to vasodilation rather than with disease.

Normal perfusion combined with no augmentation of flow is an inconclusive study: CAD has not been excluded. The recommended path is to look for a cause of the failed vasodilation and repeat if one is found, or otherwise pursue another test. The patient reported caffeine withheld for 24 hours, as the laboratory protocol required, so the study was repeated after 48 hours off caffeine.

Study #2 was markedly different. Perfusion showed a moderate, reversible inferior and inferolateral defect with TID rising to 1.29, and ejection fraction fell from 77% at rest to 62% at stress. Flow reserve remained abnormal. In the presence of a reversible defect, this combination carries high risk for CAD and cardiac events. Catheterization demonstrated three-vessel disease, and the patient was referred for coronary artery bypass surgery.

Teaching points

  • Normal perfusion with no augmentation of blood flow is an inconclusive study, not a negative one — CAD has not been excluded
  • When a culprit such as caffeine can be identified, repeat the study off caffeine; otherwise pursue CTA, catheterization, or stress echo
  • Caffeine effects can be prolonged in some patients well beyond the standard 24-hour hold
  • A 48-hour hold is not recommended for everyone, but consider it for patients who show no flow increase after 24 hours
  • A reversible defect with no rise in flow suggests severe epicardial disease with pre-existing maximal coronary vasodilation

View the full case presentationComplete slide deck comparing both studies side by side, with QC screens, perfusion and gated data, flow polar maps, and the ASNC MBFR risk classification table.

View Case Study (PDF)

References
1. Bateman TM, Heller GV, Beanlands R, et al. Practical guide for interpreting and reporting cardiac PET measurements of myocardial blood flow: an information statement from the American Society of Nuclear Cardiology and the Society of Nuclear Medicine and Molecular Imaging. J Nucl Cardiol.
2. Murthy VL, Bateman TM, Beanlands RS, et al. Clinical quantification of myocardial blood flow using PET: joint position paper of the SNMMI Cardiovascular Council and the ASNC. J Nucl Cardiol. 2018;25:269-297.

Presented in collaboration with the American Society of Nuclear Cardiology. Case images are not for diagnostic use. This material is intended for healthcare professionals and is educational in nature; it is not clinical advice for any individual patient.

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