In the era of isotope shortages and heightened awareness of radiation dose exposure, it should come as good news that if low-risk patients have a normal stress myocardial perfusion imaging study, they need not undergo the conventional complementary rest study, according to a study in the May/June issue of the Journal of Nuclear Cardiology.
W. Lane Duvall, MD, and colleagues from Mount Sinai Medical Center in New York City evaluated 1,673 patients who had a normal stress-only study and 3,237 patients who had a normal rest-stress study. All stress-only patients had a low pre-test risk for coronary artery disease (CAD).
At one year, total all-cause deaths and cardiac deaths in the stress-only group were 1.2 and 0.2 percent, respectively, and 1.2 and 0.1 percent, respectively, in the rest-stress cohort.
At the end of nearly four years of follow up, there was still no statistically significant difference between the two groups: 2.7 and 0.4 percent in the stress-only group, and 3.7 and 0.5 percent in the rest-stress cohort.
The researchers said that the advent of competing noninvasive imaging modalities, such as stress echocardiography and CT angiography, "exposed the weaknesses of conventional SPECT: That the test is unacceptably long (up to five hours, or even two days) and burdens the patients with a relatively high radiation dose."
They also detail recent innovations in camera systems, image reconstruction techniques and imaging protocols that allow shortened imaging times and lower radiation doses. Since 60 to 70 percent of SPECT studies are normal, reversing the sequence of rest-stress to stress-only if the stress is normal allows the test to be completed in 90 minutes and decreases the radiation dose by at least 30 percent.
The average patient of 186 pounds at Mount Sinai would receive a rest dose of 10 mCi of technetium-99m.
Researchers said that by reducing study time and decreasing radiation exposure, "the stress-only protocol allows SPECT MPI to more effectively compete with other imaging studies for the diagnosis of CAD in lower risk patients and addresses valid concerns about ionizing radiation from medical imaging."
Nuclear cardiologists at Mount Sinai began using stress-only imaging in 2004 for those with low-pretest probability of CAD, and for logistical reasons such as time constraints, non-cooperative patients or obesity. The current study further validates the protocol in routine clinical practice, especially one "that appears more suitable for the current need for more efficient use of modern technology," they wrote.
In an accompanying editorial, Brian G. Abbott, MD, from Brown University in Providence, R.I., noted that the study by Duvall et al brings the cumulative reported experience of performing stress-only imaging to more than 10,000 patients. Importantly, besides showing low all-cause mortality, Duvall et al showed similarly low rates of cardiac deaths.
"As such, it can now be definitively concluded that stress-only imaging protocols are safe and effective," Abbott proclaimed.