Marlene Busko

July 14, 2017

WASHINGTON, DC — In a large registry study of asymptomatic patients who had a physician-requested coronary artery calcium (CAC) CT scan, a high CAC score predicted a higher risk of death during a mean follow-up of 12 years[1].

The mortality risk increased with increasing number of five traditional cardiovascular disease (CVD) risk factors.

"A higher CAC burden is strongly associated with risk of all-cause mortality, especially CVD/CHD mortality across an increasing burden of traditional risk factors," Dr Gowtham R Grandhi (Baptist Health South Florida, Miami) reported in an oral session at the Society of Cardiovascular Computed Tomography (SCCT) 2017 Annual Scientific Meeting.

In an interview, Grandhi said that the study "has a long follow-up and a bigger study population than previous studies," but he also conceded that "[CAC] does not replace the standard risk factors as a screening tool." Still, "it can help better stratify the risk groups," he said.

However, the added value of CAC screening "is always the problem, and that question is not finally resolved" with this study, session comoderator Dr Martin Hadamitzky (Technische Universität München, Germany) cautioned to theheart.org | Medscape Cardiology.

"We know calcium scoring has an additional prognostic value, and this study suggests something like it's better than traditional risk factors, [but] I'm not convinced," he said. "Both are important."

Compared with individuals with a CAC of 0, those with a CAC >400 had a 1.8-fold to 3.2-fold increased risk of all-cause death and a 3.1 to 5.1-fold increased risk of CVD death, depending how many traditional CVD risk factors they had.

On the other hand, the study showed that having no CAC "is extremely reassuring for all-cause mortality and in particular CVD/CHD-specific mortality in long-term follow-up extending to 12 years," Grandhi said.

Interplay of CAC and Traditional Risk Factors

Little is known about the interplay of traditional CVD risk factors and cause-specific mortality in the long term, Grandhi explained.

To examine these relationships, the researchers used data from the CAC Consortium, a large multicenter observational cohort of participants who underwent noncontrast cardiac-gated CAC testing. The registry included 66,636 asymptomatic adult patients who received CAC testing at four US sites between 1999 and 2010.

The patients were grouped into four categories based on whether they had zero, one, two, or three or more of five traditional CVD risk factors (current cigarette smoking, dyslipidemia, type 2 diabetes, hypertension, and a family history of coronary heart disease).

The patients were also grouped into four categories of CAC scores (0, 1–100, 101–400, >400 Agatston units). The patients had a mean age of 54, 67% were male, and most were white (89%).

Overall, about half had a family history of coronary heart disease (46%) or dyslipidemia (54%); close to a third had hypertension (31%); one in 10 smoked, and fewer patients (7%) had type 2 diabetes.

About two-thirds of patients had one risk factor (36%) or two risk factors (32%), and the rest had no risk factor (17%) or three or more risk factors (15%).

Close to half had a CAC score of 0 (45%); 31% had a CAC score between 1 and 100; and fewer had a CAC score between 101 and 400 (13%) or >400 (11%).

The rates of current smoking and family history of CAD were similar among patients in the four CAC categories, but the likelihood of being male and the prevalence of the other CVD risk factors increased with increasing CAC scores.

Among patients with a CAC score of 0, 56% were male, 23% had hypertension, 48% had dyslipidemia, and 4% had type 2 diabetes.

However, among patients with a CAC score >400, 84% were male, 50% had hypertension, 66% had dyslipidemia, and 15% had type 2 diabetes.

CAC and Risk of Long-term Death

Mortality was determined using the Social Security Death index and the cause of death established using the National Death Index, the researchers note.

During a mean follow-up of 12 years, 3158 patients (4.7%) died, mostly from cancer (37%) and CVD (32%). Of the deaths due to CVD, 54% were due to CHD and 17% were from stroke.

Among patients with zero, one, two, or three or more risk factors, 3.4%, 4.0%, 4.9%, and 7.6%, respectively, died during follow-up.

Increasing CAC scores were associated with an increasing risk of all-cause, CVD, and CHD mortality.

Compared with patients with no CAC, those with CAC >400 and no traditional risk factors had a 1.84-fold increased risk of all-cause death during follow-up, whereas patients with three or more traditional risk factors and CAC of 1 to 100 had a 1.32-fold increased risk of this outcome.

The rates of CVD mortality for these patient groups were increased 4.07-fold and 1.52-fold, respectively.

Study limitations include potential referral bias (since all patients were referred by physician), lack of generalizability (since most patients were white), and potential recall bias (since risk factors were self-reported), Grandhi acknowledged.

Nevertheless, "I think that this study says that CAC can be used for screening purposes; it has an additional value but it does not replace risk factors," he summarized.

Grandhi had no relevant financial relationships.  

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