A community-wide evaluation of myocardial perfusion imaging (MPI) use throughout the Kaiser Permanente Northern California health system revealed an unexplainable 51 percent dip in MPI from 2006-2011, according to research published today in the Journal of the American Medical Association.

MPI underwent rapid growth in the several years that preceded 2006, but the numbers began to drop after that point and researchers are not sure why. Edward J. McNulty, MD, a cardiology specialist at Kaiser Permanente Medical Center in San Francisco, Calif., and colleagues, conducted a sweep of more than 300,000 follow-ups across the clinical database of the regional health system before making their assessment.

“After increasing from 2000 to 2006, MPI use abruptly declined through 2011 within our population,” wrote McNulty et al. “Declines for persons aged 65 and older exceeded those for Medicare free-for-service population during the same period and were even greater for younger persons. These declines could not be explained by increasing use of alternative modalities.”

The researchers noted that appropriate use criteria could be a potential factor and that there may be an overall trend in MPI as reflected by the slowdown within the Medicare fee-for-service population. Stress echocardiography use remained virtually the same during the period of decline, but use of cardiac CT did increase significantly. However they estimated that the spike in CT could only account for about 5 percent of falling MPI use. Interestingly, overall rates of myocardial infarction also fell.

“Although the abrupt nature of the decline suggests changing physician behavior played a major role, incident coronary disease, as assessed by MI, also declined,” wrote the researchers. “We could not determine the relative effects of these factors on MPI use.”

The incidence of myocardial infarction dipped 27 percent during the period of MPI decline. There were no major differences between patient gender or history of revascularization. There was a difference in the declines in MPI performed via an out-patient versus in-patient basis, 58 percent versus 31 percent, respectively.