The precise role of coronary artery calcium )CAC) scans in clinical practice has been the subject of considerable discussion and debate. Passionate advocates have been unable to persuade most physicians that obtaining routine calcium scores can help improve risk prediction and prognosis. No general consensus has yet emerged.
Now a new study published in the Journal of the American College of Cardiology offers evidence supporting a different and novel role for calcium scores. People at intermediate risk who would prefer not to take a pill can safely avoid statins if they have a zero calcium score, the new findings suggest. The study raises the possibility that about half of people who are eligible to take them might now avoid taking statins. This is particularly important because under the current guidelines statins are either recommended or may be considered for almost two-thirds of the US adult population.
“We believe that the value of CAC testing in the current era may be in limiting the scope of statin therapy to more selective use, rather than in expanding it,” the authors, led by Khurram Nasir (Baptist Health South Florida, Miami) write.
In an email interview Nasir specifically rejected the “big elephant in the room” which is the “traditionalist point of view of ‘screening’ to treat.” “Why bother when two-thirds are already candidates for treatment?”
The authors calculated that 50% of their study cohort of 4,758 MESA (Multi-Ethnic Study of Atherosclerosis) participants were eligible for statins, most because they had a 10-year estimated risk of 7.5% or greater. However, 41% of this group had a calcium score of zero. The event rate in this group was 5.2 events per 1,000 person-years.
Among patients who fall in the group for whom statins may be considered because they have an estimated 10-year ASCVD rate of 5-7.5%, 57% had a zero calcium score and a very low event rate of 1.5 events per thousand years. By contrast, the patients with some calcium had an event rate of 7.4. Among patients for whom statins are recommended because they have an event rate between 7.5 and 20%, 45% had a zero calcium score and a low event rate of 4.5 events per thousand patient years.
Calcium scores, according to the authors, would likely have only a “limited impact on decisions regarding statin utilization” at both the high and the low extremes of risk, the authors wrote. But in the group at intermediate risk, they wrote, “the absence of CAC can afford significant value in promoting shared decision-making and better informing patients, who may consider avoiding statins to focus on prudent lifestyle changes, of their choices.”
In his interview Nasir emphasized that “as far as we are concerned,” his paper makes “no recommendation for CAC testing but rather recommends shared decision making.”
In an accompanying editorial, a co-chair of the ACC/AHA cardiovascular risk guidelines, Donald Lloyd-Jones (Northwestern University) largely agrees with the authors that calcium scores are most useful for patients “in the broad middle,” where “there is room for the patient-clinician discussion espoused by recent guidelines, which could well be informed by judicious use of CAC screening.”
On the one hand, he writes, “finding a CAC score of 0 in someone otherwise thought to be in a net benefit group is a powerful reason to consider withholding statin therapy.” On the other hand, “the presence of a high CAC score in an individual at only moderate predicted risk should be a powerful motivator to initiate and adhere to statin therapy.”
We need to be careful extrapolating from epidemiological studies to real patients. Though a score of zero is better than having calcium, it all comes down to pre-test likelihood. There are many studies showing lots of MIs among people with scores of zero – but at intermediate or higher risk. See the Seattle Bay Heart Watch Study, Core 64 , and Schenker, et al (Circulation, 2008), for starters. Indeed, the latter study lead to a great editorial by Phil Greenland and Bob Bonow in the same issue (“How Low-Risk Is a Coronary Calcium Score of Zero? The Importance of Conditional Probability”). Indeed, the exact same discussion these papers have generated.
I certainly can think of situations where a person is old enough to have calcified and if their score is zero, I might out off a statin if they were on the borderline. But on the other hand, is it really worth any money and any radiation when it comes to a drug that is generic and safe? At $4/month, one can take a statin for 3 years to cover the price of the scan. Then there is the extra cost and anxiety from the 40% rate of incidental findings.
Finally, why has the strategy of treatment modification based on CAC not been put to the test of an RCT? Just because other things have not been tested (like risk factor models) does not mean strategies that involve more expense, incidental findings, and a small amount of radiation should not be. The RCT seems long overdue.