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Breaks in the supply of technetium 99m (^99mTc) -- the main radiotracer for cardiac stress testing with single-photon emission CT myocardial perfusion imaging (SPECT-MPI) -- can be linked to excess cardiac catheterizations, a study suggests.

, of University Of Michigan, Ann Arbor, and colleagues followed what happened after a 6-month shortage of ^99mTc, which is derived from highly-enriched uranium, due to shutdowns of two major nuclear reactors at the Petten High Flux and the Chalk River Laboratories facilities, located in the Netherlands and Canada, respectively.

That supply chain interruption occurred from March to August 2010, during which use of ^99mTc fell nearly a quarter from 64% of SPECT-MPI in February 2010 to in May 2010. As late as 2012, "we observed steadily declining use of SPECT-MPI throughout the study period with stable rates of stress echocardiography, CT coronary angiography, and positron emission tomography–MPI during the shortage," they reported online in JAMA Cardiology.

During the shortage, cardiac catheterization done within 90 days of SPECT-MPI was more likely (multivariable adjusted odds ratio 1.09, 95% CI 1.07-1.10). Murthy's group noted that 5,715 excess cardiac catheterizations may have occurred among stress testing patients.

The reason? A shortage of ^99mTc necessitates a switch to thallium 201 and other radiotracers. But "thallium Tl 201 is associated with higher radiation exposure and lower specificity relative to ^99mTc," the investigators noted.

Their study used a 20% random sample of Medicare beneficiaries age 65 or older who got SPECT-MPI stress testing between 2008 and 2012.

The demand for ^99mTc has researchers looking for ways to make the radiotracer from sources other than highly-enriched uranium. Yet the $143 million that the U.S. Congress set aside between 2011 and 2014 to encourage this hasn't been renewed, Murthy and colleagues noted.

What's more, "export of highly enriched uranium fuel will be banned starting in 2020, which could severely curtail production of ^99mTc," they added.

"These converging pressures on the ^99mTc supply chain have substantial clinical implications and underscore the importance of developing new production approaches and encouraging alternative testing approaches," they concluded.

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