BOSTON — The prognostic performance of pharmacologic stress myocardial perfusion single-photon emission CT shown in academic studies generalizes to daily practice, a study has shown.
“The current prognostic literature indicates that [the imaging technology] is an effective tool for coronary artery disease risk stratification, but the majority of these studies come from single institutions using expert readers. We wanted to investigate the prognostic power of the perfusion imaging variables as read by local readers in many sites across the world,” Dr. James Udelson said at the annual meeting of the American Society of Nuclear Cardiology.
To do this, Dr. Udelson of Tufts University, Boston, along with lead investigator Dr. Rory Hachamovitch, who is in private practice in Los Angeles, and their colleagues, conducted a prospective study comprising 4,989 patients with known or suspected coronary artery disease recruited from 89 centers in eight countries during 20 consecutive work days. All of the patients had been referred for clinically indicated pharmacologic stress myocardial perfusion imaging by single-photon emission CT (PS SPECT MPI). Of the study population, 48% of the patients were tested in tertiary care centers, and 26% each underwent testing in private and community centers.
The investigators did not dictate the imaging protocol for the study; rather, “each center used its own standard protocol for stress isotope image acquisition,” said Dr. Udelson. “This was an effectiveness study of real life practices,” he added. Toward this end, approximately 150 local readers from the different sites interpreted the images and reported segmental scores using the 17-segment, 4-point scoring model from which nuclear variables were converted into percent myocardium ischemic and percent myocardium fixed, as has been done in the literature, he said.
The primary end point of the study was all-cause death, “with the simple goal of identifying the incremental value of perfusion imaging data over all other data,” said Dr. Udelson.
Using scripted phone calls to each site, the investigators followed the patients for revascularization and all-cause death for 1 year after the imaging study. Excluded from the study were 212 patients who had undergone early revascularization (within 90 days after testing) and thus were excluded from the final analysis. All-cause death was reported for 155 of the remaining patients, said Dr. Udelson. The all-cause death rate in patients with abnormal MPI was 3.7%, significantly higher than the 2.2% observed in patients with normal MPI, he said, noting that the risk of all-cause death was greatest in patients with both reversible and fixed perfusion defects (5.4%), compared with patients with fixed but no reversible defects (3.2%) and patients with reversible but no fixed defects (2.5%).
In addition to abnormal MPI, other predictors of all-cause death were history of heart failure, chronic obstructive pulmonary disease, and diabetes. Controlling for these clinical variables as well as for demographic and historical data, “the MPI results were highly predictive of 1-year all-cause death,” Dr. Udelson said.
In the final multivariate model, both the percent myocardium with reversible defects and percent with fixed defects had statistically significant increased hazard ratios, expressed per 1% change, Dr. Udelson explained. “For example, an increase in the percent myocardium reversible, or ischemic, of 3% would be associated with a 15% increased risk [of all-cause death].”
“The findings indicate that the perfusion imaging variables, as read by local readers from many sites across the world, have prognostic power incremental to all of the clinical data,” said Dr. Udelson. “This generalizability has not been shown for other imaging modalities.”
This study was funded by King Pharmaceuticals Research & Development Inc., for which Dr. Udelson and Dr. Hachamovitch are paid consultants.
The multicener, internationaltrial 'was an effectiveness study of real life practices.' DR. UDELSON