Case 10

Published on 02/03/2015 by admin

Filed under Internal Medicine

Last modified 22/04/2025

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Case 10

A 45-year-old woman was referred for exercise ^99mTc-sestamibi SPECT MPI because of an abnormal ECG. She denied cardiac symptoms.

She exercised for 5:16 minutes on a Bruce protocol (7 METs). Peak heart rate was 158 beats/min (90% of maximal age-predicted heart rate). No exercise-induced symptoms were reported, and the blood pressure and ECG responses were normal.

Short-Axis SPECT Images

The short-axis SPECT images demonstrate a mild reversible defect in the anterior and anteroapical regions. The defect location and appearance are consistent with breast attenuation artifact, but the presence of defect reversibility is suggestive of ischemia.

Rotating Raw Planar Images

The rotating raw planar images demonstrate a prominent shadow due to photon attenuation by the left breast. Note that the position of the left breast shadow is higher on the poststress images (the breast shadow eclipses only the upper half of the heart). The preferential attenuation of photons emitted from the anterior wall of the left ventricle results in an anterior perfusion defect. The breast shadow is lower on the resting images and eclipses the entire heart. The resulting uniform photon attenuation does not create a perfusion defect. Therefore, shifting breast position can cause a reversible anterior wall defect that can be misinterpreted as anterior wall inducible ischemia.

The position of the breast can vary depending on the extent to which the patient’s arms are raised above the head during image acquisition. Consistent arm positioning is important to ensure consistent breast position and high-quality SPECT images.

Teaching Points: “Shifting” Breast Attenuation (See Chapter 5)

1. A change in breast position (from resting to poststress images) can result in a reversible anterior-wall perfusion defect suggestive of ischemia.

2. Careful review of raw planar images can identify the “shifting” breast attenuation pattern.

3. Be cautious in attributing a reversible perfusion defect to “shifting breast attenuation artifact,” especially if other markers of ischemia are present (e.g., exercise-induced chest pain or ST-segment depression). For confirmation, this patient underwent rubidium-82 PET MPI, which demonstrated normal homogeneous rubidium-82 uptake in all myocardial regions. PET MPI studies employ robust attenuation correction, and therefore breast attenuation (and other soft-tissue attenuation) artifacts are less problematic.

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