- Due to shortages of a radioactive substance used in exercise stress tests, more heart patients have needed complex invasive procedures, new research shows.

Doctors inject the harmless radioactive substance, called a tracer, to help them diagnose or rule out coronary artery disease. Not every patient needs the injection. But for those who do, not being able to get it means the only other way for doctors to get the same information is for the patient to undergo a cardiac catheterization.

In a cardiac catheterization, doctors thread a tube from an artery in a patient's wrist or groin all the way into the heart, to look for blockages of the coronary vessels.

More on this...

The current worldwide shortage of a radioisotope known as technetium Tc 99m, which is commonly used during stress testing, appears to have led to a nearly 10 percent increase in heart catheterizations after stress tests, Dr. Venkatesh L. Murthy from the University of Michigan in Ann Arbor told Reuters Health.

"Due to the complexities of the healthcare system, it isn't that often that we can tie supply chain issues such as this to direct healthcare outcomes," Murthy said.

Cardiac stress tests use technetium 99m to evaluate the blood supply to the heart, but recent shutdowns of nuclear reactors have resulted in significant shortages. Doctors have had to turn to other radioactive tracers, like thallium 201, but it is associated with higher radiation exposure and less accurate results.

Murthy's team used information from Medicare to investigate how these shortages affected cardiac stress testing and the use of cardiac catheterization among individuals age 65 or older.

Between 2010 and 2012, technetium 99m use decreased by nearly 25 percent, while the rates of other tests used to evaluate coronary artery disease remained stable.

However, cardiac catheterization rates within 90 days after testing that would have used technetium 99m or thallium 201 increased by 9 percent. This translates into 5,715 extra cardiac catheterizations among these Medicare patients.

For a variety of reasons, the researchers note, shortages of technetium are likely to continue.

"Shortages of important medical compounds can have substantial clinical consequences," Murthy said in an email. "In this particular case, shifting to thallium-201 during future shortages of technetium-99m may not be the optimum strategy, and greater use of other tests, such as positron emission tomography (PET), magnetic resonance imaging (MRI) and computed tomography (CT), may be a better alternative."

"There are efforts to address this issue by many groups," he said. "Several companies have developed technologies to produce the technetium without using weapons-grade uranium. What is not completely clear yet is whether they will be able to operationalize these technologies and ramp up supply quickly enough."