Interrelation of Coronary Calcification, Myocardial Ischemia, and Outcomes in Patients with Intermediate Likelihood of Coronary Artery Disease

Schenker et al. Circulation 2008;117:1693-1700

Recent years have witnessed the increasing use of atherosclerosis testing by means of calcium scoring (CAC) or non-invasive coronary angiography, in addition to functional testing. However, whether also additional prognostic value can be derived from these tests remains to be determined.
In the current article Schenker et al. report on the comparison and follow-up of 621 patients (at mainly intermediate risk, mean age 61 ±13 years, 40.9% male) who underwent both positron emission tomography (PET) myocardial perfusion imaging (MPI) and CAC scoring.

Baseline comparison of techniques

In total, 179 patients had abnormal PET MPI, which were mainly (134 (75%) small defects, although 15 patients (8%) showed large defects (>20%). CAC was on average 429±869, and was significantly higher in those with abnormal PET MPI (750±1195 versus 299±652 in patients with normal PET MPI). In line with this observation, the frequency of abnormal MPI increased with increasing CAC scores. Nevertheless, also in patients without any calcium, ischemia was frequently noted (16%). In addition, multivariate logistic regression analysis was performed to determine predictors for ischemia. The analysis which was controlled for age, sex, conventional risk factors, and symptoms revealed CAC score to be the strongest independent predictor of abnormal PET MPI. Prediction was strongest for CAC  400; with an odds ratio of 2.9.

Survival analysis

During a mean follow-up of 524±212 days (minimum 15, maximum 866), a total of 55 events occurred, including 33 deaths and 22 non-fatal myocardial infarctions. Cox regression analysis showed that both ischemia on PET MPI and a CAC score  1000 were significant predictors of events. Importantly, CAC score enhanced risk stratification in patients with and without ischemia on PET MPI, indicating incremental prognostic value for CAC over MPI.

Conclusion:

Accordingly, the authors conclude that stress perfusion imaging is limited in its ability to detect subclinical atherosclerosis, although absence of CAC does not exclude the possibility of flow-limiting CAD. In addition, patients with and without ischemia on PET MPI showed a stepwise increase in their risk of cardiac events in line with increasing CAC scores. Thus, the combination of anatomical and functional information may allow improved risk stratification, although these observations will need to be confirmed in larger multi-center trials. Also these studies should address whether this approach has the potential to improve clinical management.