Case 6

Published on 02/03/2015 by admin

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Last modified 22/04/2025

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Case 6

A 69-year-old woman was referred for adenosine stress SPECT MPI for evaluation of dyspnea and chest pressure. She had a history of stent placement in the mid-LAD 3 years previously.

Adenosine was infused at 140 mcg/kg/min over 4 minutes. She was unable to perform low-level treadmill exercise during the infusion. No symptoms were reported during the adenosine infusion, and her blood pressure and ECG responses to adenosine were normal.

Raw Images

The raw planar images demonstrate moderate photon attenuation by the left breast (the bra cup size is 40 D). There is chest-wall adipose tissue present, resulting in further soft-tissue attenuation. The patient’s body mass index is 37 (>30 = obese). In addition, there is marked hepatic and gastrointestinal (GI) tracer activity in close proximity to the heart. GI tracer interference is frequently problematic with pharmacologic stress, particularly when the patient is unable to perform low-level treadmill exercise during the infusion.

SPECT Tomograms

SPECT images demonstrate a mild defect in the distal anteroseptal region, with very mild defect reversibility on resting images. The defect could be consistent with breast attenuation artifact, though the mild defect reversibility raises concern for ischemia (possibly in the territory of the prior LAD stent placement). There is also a mild defect in the inferior and inferolateral regions, and subtle defect reversibility is evident on resting images. This stress defect (and the subtle defect reversibility evident on resting images) might be entirely due to GI tracer interference. Ischemia cannot be confidently excluded.

Quantitative Polar Map

When the perfusion pattern of this woman was compared to a female-specific normal database, the distal anteroseptal defect was judged to be within normal limits. Female-specific normal databases take into account the expected reduction in tracer activity in this region, owing to breast attenuation. However, the inferior/inferolateral wall stress perfusion defect was judged to be abnormal by quantitative criteria, and subtle defect reversibility was detected, suggesting the presence of inducible ischemia.

Gated SPECT Images

Gated SPECT images show normal myocardial systolic thickening in all regions, with a normal computed LVEF (58%). In the setting of nonreversible perfusion defects, the assessment of myocardial systolic thickening is useful for distinguishing defects caused by soft-tissue attenuation from defects caused by myocardial infarction. However, in the setting of completely or partially reversible defects, the presence of normal myocardial systolic thickening cannot be used to confidently exclude the presence of inducible myocardial ischemia.

She was referred for rubidium-82 (⁸²Rb) PET MPI.

Because there was significant diagnostic uncertainty present after SPECT MPI, the patient was subsequently referred for dipyridamole stress ⁸²Rb PET MPI.

PET Tomograms

The peak stress ⁸²Rb PET images demonstrate a severe perfusion defect in the inferior region, extending from the base to the apex. The resting images show uniform ⁸²Rb activity in all myocardial regions, including the distal anteroseptal region (where breast attenuation was noted on the SPECT MPI study). PET images are routinely corrected for soft-tissue attenuation, and therefore PET MPI provides a more reliable assessment of regional myocardial perfusion, irrespective of gender or body habitus. Note that mild GI tracer activity is present on the peak stress and resting ⁸²Rb perfusion images. However, because of the superior spatial resolution of PET (compared to SPECT), the GI tracer activity does not result in problems with PET image interpretation.

Also note that the left ventricular cavity appears larger on peak stress images compared to resting images. An increased peak stress-to-rest left ventricular cavity ratio is frequently observed on PET MPI in the setting of inducible ischemia. This finding is seen more frequently with PET MPI than with SPECT MPI.

Gated PET Images

The ⁸²Rb PET images are gated both at rest and at peak stress. The ability to measure regional and global left ventricular systolic function at peak stress is a unique advantage of PET MPI. In this case, the LVEF was normal (73%) on resting gated PET images, but the LVEF decreased to 62% at peak stress. A decrease in computed LVEF is frequently observed during dipyridamole stress in patients with extensive coronary artery disease and inducible myocardial ischemia. A decline in LVEF from rest to peak stress is an additional marker of ischemia on gated PET MPI. This marker is especially useful in detecting balanced myocardial ischemia due to multivessel coronary artery disease. In such cases, the peak stress myocardial blood flow may appear homogeneous due to similarly decreased blood flow reserve in all myocardial regions.

Coronary Angiography

The coronary angiogram confirmed that the LAD stent remained widely patent. However, the right coronary artery (RCA) was totally occluded, and the RCA territory was fed by collateral vessels. The presence of RCA disease was confidently and accurately predicted by the PET MPI study, while the SPECT MPI study was equivocal for ischemia in this region.

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Case 6

A 69-year-old woman was referred for adenosine stress SPECT MPI for evaluation of dyspnea and chest pressure. She had a history of stent placement in the mid-LAD 3 years previously.

Adenosine was infused at 140 mcg/kg/min over 4 minutes. She was unable to perform low-level treadmill exercise during the infusion. No symptoms were reported during the adenosine infusion, and her blood pressure and ECG responses to adenosine were normal.

Raw Images

The raw planar images demonstrate moderate photon attenuation by the left breast (the bra cup size is 40 D). There is chest-wall adipose tissue present, resulting in further soft-tissue attenuation. The patient’s body mass index is 37 (>30 = obese). In addition, there is marked hepatic and gastrointestinal (GI) tracer activity in close proximity to the heart. GI tracer interference is frequently problematic with pharmacologic stress, particularly when the patient is unable to perform low-level treadmill exercise during the infusion.

SPECT Tomograms

SPECT images demonstrate a mild defect in the distal anteroseptal region, with very mild defect reversibility on resting images. The defect could be consistent with breast attenuation artifact, though the mild defect reversibility raises concern for ischemia (possibly in the territory of the prior LAD stent placement). There is also a mild defect in the inferior and inferolateral regions, and subtle defect reversibility is evident on resting images. This stress defect (and the subtle defect reversibility evident on resting images) might be entirely due to GI tracer interference. Ischemia cannot be confidently excluded.

Quantitative Polar Map

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