NEW YORK — A coronary calcium score was an effective, initial screen for coronary artery disease in asymptomatic patients with type 2 diabetes in a study of 510 patients.
Coronary calcium “may be the most cost effective and feasible way” to screen patients with diabetes, Vijay Anand, M.D., said at the annual meeting of the American Society of Nuclear Cardiology.
Physicians are currently seeking the best way to identify coronary artery disease in asymptomatic patients with diabetes, because they know that coronary disease is highly prevalent in this group but often progresses to a severe stage before any clinical symptoms appear.
Myocardial perfusion imaging (MPI) has also shown value as a noninvasive way to identify asymptomatic coronary disease in patients with diabetes, but “we can't do MPI on every diabetic—we could not afford it,” said Avijit Lahiri, M.B., director of cardiac imaging and research at Wellington Hospital in London and a collaborator in the new study. In the study, MPI was used to confirm the presence of coronary disease. “We were horrified to see that almost half of the asymptomatic patients with diabetes had coronary calcification,” he added.
“Coronary calcium is potentially a good way to screen patients with diabetes, but we need more data,” commented Frans J. Th. Wackers, M.D., director of the cardiovascular nuclear imaging and exercise laboratory at Yale University, New Haven. “Coronary disease is common in patients with diabetes and can form quickly.”
The study included patients aged 30-65 years who had been diagnosed with type 2 diabetes for at least 1 year who were under treatment at any of four community clinics in the United Kingdom. Of 927 patients initially assessed for the study, 510 met the enrollment criteria and were willing to participate. Their average age was 53 years, and they had been diagnosed with diabetes for an average of 8 years. Their average serum glycosylated hemoglobin was 8.2%.
An initial examination by electron beam CT showed that 46% had a score of 10 or higher, which was defined as significant coronary calcification: Twenty percent had a score of 10-99, 15% had a score of 100-399, and 11% had a score of 400 or more. There was no correlation between calcium scores and serum levels of either C-reactive protein or interleukin 6, two markers of inflammation, said Dr. Anand, a cardiologist at Wellington Hospital and Royal Free Hospital in London.
All 235 patients with a significant calcium score, as well as a random sample of 50 patients from those with a score of less than 10, underwent MPI using a stress-rest protocol with technetium 99m sestamibi and dipyridamole and maximum treadmill exercise.
Among the 50 patients with calcium scores of less than 10, none had myocardial perfusion defects detectable by MPI. In contrast, perfusion defects were detected in 18% of patients with calcium scores of 10-99, 23% of those with scores of 100-399, 48% of those with scores of 400-999, and 71% of those with scores of 1,000 or greater, said Dr. Anand. The majority of perfusion defects seen with MPI were reversible.
In a multivariate analysis that controlled for a variety of clinical and metabolic variables, the strongest predictors of myocardial perfusion defects on MPI were high calcium scores.
Patients with scores of 400-999 had a 5.3-fold increased risk of having MPI defects, compared with those who had scores of less than 100. Patients with scores of 1,000 or higher had a 7.1-fold increased risk of having myocardial perfusion defects. Patients with calcium scores of 100-399 had a 40% increased risk compared with patients with scores of less than 100.
The only other predictors of perfusion defects were male gender, which raised the risk 2.75-fold compared with women, and the presence of peripheral neuropathy, which doubled the risk, compared with patients without peripheral neuropathy.
Additional analysis showed that including coronary calcium scores with other, conventional risk factors resulted in the identification of 75% of the patients' risk of having perfusion defects on MPI. Conventional risk factors alone accounted for 62% of the risk.
“The addition of coronary calcium scores added incremental, predictive information,” Dr. Anand said.