Diabetes, No Coronary Calcium: Still Worse Long-term Survival

Marlene Busko

February 25, 2016

NEW YORK, NY — Asymptomatic individuals with diabetes who have a coronary artery calcium (CAC) score of zero have a favorable 5-year survival, but beyond that, out to 15 years, the risk of death is higher in individuals with diabetes than in those without diabetes, suggests a new study[1].

"To our knowledge, this study is the first to demonstrate that CAC is associated with an increased risk of long- but not short-term mortality" in patients with type 2 diabetes, Dr Valentina Valenti (New York Presbyterian Hospital and the Weil Cornell Medical College) and colleagues report in this study, published online February 4, 2016 in Circulation: Cardiovascular Imaging.

These findings extend those of their previous research that showed that individuals with diabetes and a CAC of zero have a "warranty period" of 4 years where they remain free of coronary artery calcification.

In an accompanying editorial[2], Dr Udo Hoffmann (Harvard Medical School, Boston, MA) writes that importantly, the current study suggests that patients with diabetes need more frequent screening. "The data suggest that a calcium score of 0 predicts a low risk (akin to a warranty period) for ≤5 years in patients with diabetes mellitus and ≤15 years in those without diabetes mellitus," he writes. "Probably the most important implication . . . is that adequate intervals for observation for subclinical CAD may be 5 years in patients with diabetes mellitus and 15 years in those without," according to Hoffmann.

The study emphasizes that "all diabetic patients are not alike," Dr Donald W Bowden (Wake Forest School of Medicine, Winston-Salem, NC), who leads the Diabetes Heart Study and was not involved with the current study, commented to heartwire from Medscape. "Some people triple the amount of plaque they have in a year, and in some people it doesn't change at all," so the patients who died during study follow-up may have had more rapidly progressing coronary artery calcification, he speculated. The study shows that more frequent monitoring is needed to assess cardiovascular disease risk in patients with diabetes, he agreed.

CAC, Diabetes, and Long-term Mortality

Previous studies have shown that asymptomatic individuals, including those with type 2 diabetes, who do not have coronary artery calcification have a good 5-year prognosis, but outcomes beyond that are unknown, Valenti and colleagues write.

The researchers aimed to investigate the usefulness of CAC screening to predict long-term prognosis in asymptomatic diabetic individuals. Their secondary objective was to see if the prognostic role of CAC differed in diabetic and nondiabetic individuals.

They enrolled 9715 consecutive asymptomatic individuals without known CAD who were referred to their center to undergo CAC testing.

The patients had a mean age of 53 and 59% were men. They had an electron-beam CT scan and replied to questions that revealed that 8.3% had type 2 diabetes, 39% were current smokers, 63% had dyslipidemia, 43% had hypertension, and 69% had a family history of premature CAD.

The patients were stratified into four levels of CAC scores (0, 1–99, 100–399, and >400). Half of the patients had a CAC >0. Individuals with diabetes had a higher extent of CAC.

During a median follow-up of 15 years, 936 patients (9.6%) died. More diabetic than nondiabetic individuals died (23.2% vs 8.4%; P<0.0001).

Among patients with CAC scores of 0, the risk of mortality at 5 years was similar for diabetic and nondiabetic individuals (2.55% and 1.24%, respectively), but by 15 years, mortality had increased much more in diabetic than nondiabetic individuals (11.7% vs 4.5%, respectively).

At 15 years, compared with diabetic patients with a CAC score of 0, those with the highest CAC scores (>400) had a 3.41-fold higher risk of death; in nondiabetic patients, compared with those with a CAC score of 0, those with the highest CAC scores had a 4.64-fold higher risk of death, after adjustment for multiple variables.

CAC scores improved the prediction of long-term all-cause mortality beyond the traditional risk factors for diabetic and nondiabetic individuals.

The researchers acknowledge that this was single-center study (which limits generalizability), CAC and clinical risk were only assessed once, and the patients' cause of death was not known.

Nevertheless, the findings suggest that "CAC may prove useful for identifying diabetic individuals prone to a greater burden of mortality and may facilitate therapeutic decision making within a clinical setting," they write.

According to Hoffmann, "Efficacy trials comparing imaging- and non–imaging-guided prevention strategies in diabetic patients would provide the ultimate proof of whether imaging could indeed be beneficial and affordable."

Valenti had no relevant financial relationships; disclosures for the coauthors are listed in the article. Hoffmann reports receiving grants from American College of Radiology Imaging Network, HeartFlow, and Siemens Healthcare on behalf of his institution.

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