Zero calcium, zero events?

Atherosclerotic cardiovascular diseases remain the number one killer in the world, accounting for nearly one-third of all deaths worldwide. There is a clinical dilemma, in that almost half of acute coronary events occur in previously asymptomatic patients, and nearly 70% of acute coronary events result from coronary lesions that are not hemodynamically significant or flow-limiting before the event. Thus, it is important to identify patients at risk for future cardiovascular events. Multiple scoring systems have been developed to predict the risk of coronary events in patients who do not have a history of cardiovascular diseases, but are at risk for future events. The Framingham risk score (FRS) is probably the most extensively adopted one. The main problem for FRS, is that it does not incorporate family history and many components of metabolic syndrome. Furthermore, it has been reported that more than 60% of coronary atherosclerotic events occurred in patients who were in lowor intermediate-risk categories. It would be important to look for other imaging modalities, to identify patients in the intermediate FRS group, who may have increased risks of coronary events. The coronary artery calcium (CAC) score, obtained by CT scan, has become useful in providing additional prognostic information independent of FRS. In a study involving 3529 asymptomatic patients from the Framingham Offspring Cohort, applying CAC scoring, re-classified the low and intermediate FRS risk patients into lowerand higher-risk strata. What is more interesting is the prognostic value of the CAC score of zero. The issue has been intensively debated in recent years. The negative predictive value of zero CAC score critically depends on the presence of symptoms. In a cohort of 25,253 consecutive asymptomatic individuals for CAC, scanning, the 10-year survival was 99.4% for patients with zero CAC score. In a recent meta-analysis involving more than 29,000 asymptomatic patients with a zero CAC score, with a mean follow-up period of 50 months, the annual event rate was only 0.12%. A zero CAC score was more reassuring than a negative intimamedia thickness test or negative stress test to be protective from cardiovascular events. Furthermore, diabetic patients who had a zero CAC score had a similar cardiovascular risk to those without diabetes. For symptomatic patients, the absence of CAC is unable to exclude obstructive coronary artery disease. This has been