Prognostic significance of zero coronary calcium scores on cardiac computed tomography

BackgroundMost unexpected cardiovascular events occur in persons at intermediate risk of coronary artery disease (10%–20% 10-year risk). Coronary artery calcium (CAC) has been shown to be highly specific for atherosclerosis, occurring only in the intima of the coronary arteries. Evidence shows that elevated coronary calcium scores (CCSs) are predictive of future cardiovascular events, both independently of and incrementally to conventional cardiovascular risk factors. Several studies reported event rates of zero for those persons without CAC by cardiac computed tomography (CT).ObjectivesWe sought to evaluate the event rates in persons with negative calcium scores from the reported literature to establish whether these patients may be considered at low risk for hard cardiovascular events (myocardial infarction and death).MethodsEnglish-language studies from January 1, 1975, through February 1, 2007, were retrieved using MEDLINE and Current Contents databases, bibliographies, and expert consultation.ResultsSummary data show that in a total follow-up of 35,765 asymptomatic persons, 16,106 (45%) had scores of zero. Pooled sensitivity for CAC to detect a cardiovascular event was 98.1% [95% confidence interval (CI), 95.1%–99.9%], and negative predictive value was 99.9% (95% CI, 98.9%–100%). There were 48 hard events in this population, with an annual event rate of 0.027%.ConclusionThese large observational cohorts show that the absence of CAC by cardiac CT is associated with a low adverse event risk and therefore could be used as a tool to counsel patients about their risk of such events.