Background: While asymptomatic patients should have a lower risk of cardiac events compared to symptomatic patients referred for cardiac stress testing, comparable event rates have been noted in some prior prognostic studies. To test if a high burden of undetected atherosclerosis among asymptomatic patients helps explain such findings, we compared atherosclerotic burden, as measured by coronary artery calcium (CAC) scanning, in propensity-matched groups of volunteers and asymptomatic patients.
Methods: CAC scans were performed on a research basis in 136 asymptomatic patients referred for exercise myocardial perfusion SPECT and in 1,398 volunteers. We performed matching by propensity scores to compare volunteers with the same CAD risk factor profile as our asymptomatic patients.
Results: Among our matched groups, asymptomatic patients had significantly greater mean CAC scores than volunteers (394 ± 805 vs 151 ± 349, P = .001), primarily due to a higher frequency of CAC scores >1,000 (15.4% vs 2.5%, P < .001). Inducible myocardial ischemia by SPECT was present in 7% of patients, but was selectively concentrated among those with CAC scores >1,000, occurring in 27.0% of such patients vs only 1.9% among patients with CAC scores <1,000 (P < .0001).
Conclusions: In contrast to asymptomatic volunteers, asymptomatic patients referred for cardiac stress testing possess more extensive atherosclerosis as measured by CAC. Among asymptomatic patients with high CAC scores, the frequency of concomitant inducible myocardial ischemia is high. These results help explain prior prognostic studies concerning asymptomatic patients and indicate the importance of making a clinical distinction between healthy subjects and asymptomatic patients with respect to atherosclerotic risk.