Diffuse breast uptake of technetium-99m tetrofosmin during myocardial perfusion imaging in a lactating mother

Abstract

Myocardial perfusion imaging (MPI) is a useful modality to rule out myocardial ischaemia in patients presenting with chest pain. In nursing mothers imaging with radioisotope is usually avoided but under certain circumstances it is unavoidable. We present the case of a 45-year-old woman with chest pain, who underwent MPI for assessment of ischaemia. The scan showed anterior artefact due to diffuse breast uptake in both the breasts, as the patient was a lactating mother. The case highlights the importance of breast uptake of radioisotope in the lactating mother on MPI and the necessary steps which need to be taken if radiotracer is injected into a lactating woman.

Background

Coronary artery disease (CAD) is one of the leading cause of death worldwide.¹ Various diagnostic modalities are available for workup of patients, presenting with chest pain and suspected CAD. Non-invasive imaging has attained a dominant role in the diagnosis and prognosis of CAD.²The choice of the imaging modality depends on various factors including patient’s risk profile, gender and body habitus. Single-photon emission CT (SPECT) myocardial perfusion imaging is a useful imaging modality which is extensively used.³ The diagnostic yield of myocardial perfusion imaging is well known and a meta-analysis of 79 studies, including 8964 patients has validated the sensitivity and specificity to be 86% and 74%, respectively.⁴ Various radioisotopes are used in myocardial perfusion imaging and one of the commonly used radioisotope is technetium 99m (mTc99). Imaging with radioisotope is usually avoided in nursing mother but under certain circumstances it is unavoidable. When a lactating mother undergoes a nuclear myocardial perfusion scan, a fraction of the injected radiopharmaceutical may be secreted in breast milk and may end up being a source of exposure to the breastfed child,⁵ hence women undergoing such investigations are advised to withhold breast feeding for a certain period of time.⁶

Case presentation

We present the case of a 45-year-old woman who was a mother of two children. She was a known case of hypertension with a family history of premature CAD. She visited cardiology clinic with chest pain on exertion and a stress test was advised for further workup. As stress echo was not possible due to poor echocardiographic windows, she underwent myocardial perfusion imaging, after a detailed discussion of pros and cons of the procedure with the patient. It was around 10 months after the delivery when the patient presented and the test was done. The patient exercised for 10 min on Bruce protocol to a heart rate of 160 beats/minute (91% age predicted maximum heart rate), stopping for fatigue. Her baseline ECG revealed sinus rhythm and no other abnormalities. During the test, ECG at stage IV showed 1 mm horizontal ST depression in leads V5 and V6 which reverted to baseline in 3 min into recovery. The patient did not experience any chest discomfort or any other significant cardiac symptoms. During the stress part of the test, the patient was injected 700 Mbq of intravenous Tc-99m tetrofosmin for stress SPECT imaging. Same day rest SPECT imaging with 260 Mbq of Tc-99m tetrofosmin was obtained. Scan revealed no fixed or reversible perfusion defect but breast attenuation was visible. On evaluation of raw data, abnormal diffuse uptake was noted in both the breasts as patient was a lactating mother (figures 1 and 2). No stress-induced cavity dilatation was seen and left ventricular systolic function was normal at stress with no wall motion abnormalities. Postscan, the patient was counselled about further precaution for handling the baby and lactation that is, to discard 3–4 feeds completely postinjection and stay away from the baby for same period.

Figure 1.

Myocardial perfusion scan.

Figure 2.

Raw data showing bilateral diffuse breast uptake.

Treatment

In such circumstances, only supportive care is needed as radioisotope activity decays by itself. Women undergoing such investigations are advised to withhold breast feeding for a certain period of time.⁶ In our case, we advised the mother about further precautions for handling the baby and lactation that is, to discard 3–4 feeds completely postinjection and to stay away from baby for the same period.

Outcome and follow-up

The patient and the baby remained stable on follow-up.

Discussion

Imaging with radioisotope is usually avoided in nursing mother but under certain circumstances, it is unavoidable in such patients. Some patients have poor echocardiographic windows due to obesity, thick chest wall and chronic obstructive air way disease. In these patients, usually contrast is used during stress echo for better image quality and correct interpretation. Our patient was relatively obese with thick chest wall and large pendulous breasts. Unfortunately, contrast is not available in Pakistan and we cannot get better images while doing stress echo. She was intermediate risk for CAD. Simple treadmill stress test could also be done but was not preferred due to the low sensitivity of the test and chances of false positive test in case of females.⁷ Again Computed Tomography Angiography (CTA) could also be ordered but the radiation exposure and the difficulty in controlling the heart rate in an anxious female were the limitations.

Breast uptake of radioisotope may occur in the lactating mother. The uptake is seen as an artefact and may hinder the interpretation of myocardial perfusion scan. In such a situation the analysis of raw data is always useful. Tc99m tetrofosmin is a small cationic complex of technetium which remains in circulation postinjection for a trivial period and after 10 min only <5% of the injected radiopharmaceutical remains in active circulation. There is preferential uptake by the muscles including myocardium and other tissues, with cells having property of rapid metabolism and increased energy demand as it concentrates in the mitochondria of such tissues.⁸ Tc99m tetrofosmin has a half-life of half an hour for liver and up to 4 hours for the heart while usually only faint uptake is evident in the breast or axilla.⁸

Various patterns of radioisotope uptake in the breast have been described. A prior study has retrospectively studied 20 nuclear scans⁹ and four patterns of uptake were described, that is, focal (more intense subareolar uptake in collecting ducts), crescent (more intense peripherally in breast tissue), full (sum of uptake in collecting ducts and peripheral breast tissue) and irregular (combination of breast uptake patterns and is patchy). Characteristic full bilateral uptake as seen in our patient was seen in 40%.⁹ In the past studies, it has been seen that for Tc99m labelled radiopharmaceuticals, the total excreted fraction was between 3% and 10%.¹⁰ It was recommended that when Tc99m labelled radiopharmaceuticals are used, the child should be fed just before the administration of the radionuclide and that the next three milk fractions should not be used and discarded.¹⁰ For the aforementioned radiopharmaceutical the activity concentration in the milk decreased exponentially with an effective half-life of approximately 4 hours. Moreover much smaller amounts are excreted in the breast milk. The absorbed dose to various organs of the baby has been calculated and was non injurious.

After administration of mTc99, an estimated 0.03% of the initially injected isotope is excreted in breast milk, while estimated effective dose to which infant is exposed is around 0.52 rem/mCi. According to these estimates, even at the peak concentration of radioisotope in breast milk (3 hours after Tc-99m administration), the total effective radiation dose to the infant is negligible (ie, 5.2 mrem).⁶ In our case, the patient was feeding her child frequently that is, every 2–3 hour so after discussing with her in view of above evidence we conservatively advised our patient to to avoid 3–4 breastfeeds, which corresponds to the total duration of 6–12 hours. We also advised our patient to avoid contact with baby for the same period.

Learning points.

• Nuclear imaging should be avoided in lactating women where ever possible.

• History taking prior to scan is of key importance to rule out above status.

• When nuclear imaging is unavoidable, it is essential to take necessary precautions to limit the exposure to the baby, that is, keeping safe distance for a certain time based on isotope used.

• Lactating women undergoing such procedures should be given a thorough advice on avoiding breast feeding and discarding feeds for a certain time.