Background: The selection of patients for cardiac stress tests is generally based on assessment of chest pain symptoms, age, gender, and risk factors, but recent data suggest that coronary artery calcium (CAC) measurements can also be used to predict inducible myocardial ischemia. However, the potential influence of clinical factors on the relationship between CAC measurements and inducible ischemia has not yet been investigated.
Methods and results: We prospectively performed CAC scanning in 648 patients undergoing exercise myocardial perfusion single photon emission computed tomography. The frequency of ischemia on myocardial perfusion single photon emission computed tomography was assessed according to CAC magnitude after dividing patients according to chest pain symptom class and Bayesian likelihood of angiographically significant coronary artery disease (ASCAD). Estimates of ASCAD likelihood and CAC scores were poorly correlated. The frequency of inducible myocardial ischemia was very low among patients with a low ASCAD likelihood if CAC scores were less than 400. By contrast, the threshold for increasing ischemia occurred at low CAC scores among patients with a high ASCAD likelihood. When characterized by chest pain classification, asymptomatic and nonanginal chest pain patients had a low frequency of ischemia if CAC scores were less than 400, whereas lower CAC scores did not exclude ischemia among typical angina or atypical angina patients.
Conclusions: CAC scores predict myocardial ischemia, with a threshold score of greater than 400 among patients with a low likelihood of ASCAD and those who are asymptomatic or have nonanginal chest pain. These data appear to extend the pool of patients for whom CAC scanning may be useful in ascertaining the need for cardiac stress testing.