AUC Sharpen SPECT Chest-Pain Risk Stratification in Large Series

September 13, 2013

CHICAGO, IL — Appropriate use strengthens and inappropriate use weakens the prognostic value of single-photon-emission computed-tomography (SPECT) myocardial perfusion imaging (MPI) in patients with known or suspected ischemic heart disease, "even in contemporary community-based settings," conclude investigators[1], who applied 2009 appropriate-use criteria (AUC)[2] to a series of >1500 outpatients. An accompanying editorial, however, says the findings are helpful but don't necessarily apply broadly and conclusively to US clinical practice[3].

Dr Rami Doukky (Rush University Medical Center, Chicago, IL) and associates stratified the cohort, obtained from 20 primary-care and two cardiology practices, according to appropriateness of receiving technetium-99m sestamibi SPECT imaging according to the AUC and tracked them for a mean of 27 months.

The 11% of patients with myocardial perfusion defects ("abnormal" scans) indeed showed significantly increased rates of major adverse cardiac events (MACE) and coronary revascularization. And among patients with scans judged appropriate (51.6% of the cohort) plus those with scans of "uncertain" appropriateness (2.9%), the MACE rate climbed sharply when the scan was abnormal.

But no such significant MACE increases with abnormal scans were seen for the remaining 45.5% of patients in whom scans were considered inappropriate.

Hazard Ratio (95% CI) for Outcomes by AUC Appropriateness Category

End point Appropriate/uncertain, n=823a Inappropriate, n=688b
Death 3.1 (1.4–6.6) 2.3 (0.25–21.1)
Death or MI 3.3 (1.6–6.5) 4.0 (0.7–21.8)
Cardiac death or MI 3.7 (1.5–9.3) 11.8 (0.6–231.1)

a. The risk increases remained significant after researchers controlled for clinical features

b. p=NS for all

"The authors suggest that previously published data based on tertiary-care-center experience likely included higher-risk populations. We agree," state Drs Raymond J Gibbons and Todd D Miller (Mayo Clinic, Rochester, MN) in the accompanying editorial. "They were younger with a lower rate of previous MI, previous PCI, and previous CABG. All of these factors define a lower-risk population and likely account for the lower cardiac-event rates found in this study."

Moreover, they write, "the 'inappropriate rate' demonstrated in this study is more than twice as high as any previously published inappropriate rate. This finding has major implications if it is representative of other community practices in the country."

But they don't see it that way. "Are these findings generalizable, that is, should they be viewed as 'representative'?" Gibbons and Miller ask. "We think not. First, the rate of appropriate/inappropriate studies, subsequent cardiac event rates, and the prognostic value of SPECT are heavily dependent on the patient population studied. Since this study included many low-risk patients, these results likely only apply to similar low-risk patients."

More important, they note, the study shows "substantial differences" in AUC classifications between the cardiology and primary-care practices and an even wider gulf between lower and higher inappropriate-use rates across all physicians represented by the entire patient cohort.

"At one end of the spectrum, one physician had an inappropriate rate of only 10%; at the other end, one physician had an inappropriate rate of 77%. It is unlikely that the results of the current study apply to either one of these two individuals," they write. "To the degree that there is similar, if not greater, variability in physicians across the country, the 'group' results presented here may not apply to many individual physicians or many practices with higher or lower rates of inappropriate studies."

Gibbons and Miller conclude, "We need more studies such as this one to better define the variability in inappropriate rates, the most common inappropriate indications, and the prognostic value of AUC in other populations."

The study was funded by Astellas Pharma; Doukky discloses being on the company's advisory board. Disclosures for the coauthors are listed in the paper. Gibbons discloses consulting for Lantheus Medical Imaging and receiving honoraria for speaking from AstraZeneca. Miller discloses consulting for Astellas Pharma.

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