Coronary Artery Calcium and Cardiovascular Risk in Diabetic/Hypertensive Patients

Abstract & Commentary

By Harold L. Karpman, MD, FACC, FACP, Clinical Professor of Medicine, UCLA School of Medicine. Dr. Karpman reports no financial relationships relevant to this field of study.

Synopsis: Patients with hypertension and diabetes mellitus can be stratified into a lower cardiovascular risk group in the absence of coronary artery calcium.

Source: Shemesh J, et al. Relation of coronary artery calcium to cardiovascular risk in patients with combined diabetes mellitus and systemic hypertension. Am J Cardiol 2012;109:844-850.

Coronary artery calcium (CAC) as measured using computed tomography (CT) has become well accepted as a reliable marker of the total burden of coronary atherosclerosis.1,2 The presence of CAC in an asymptomatic population has been demonstrated to indicate the presence of subclinical coronary heart disease (CHD) usually associated with an increased cardiovascular risk.3-5 Certain disease states — such as hypertension,6 chronic renal failure,7 diabetes mellitus (DM),8,9 and cigarette smoking10 — have been demonstrated to significantly increase the risk of cardiovascular (CV) disease. The concept that type 2 DM is a CHD equivalent has been challenged by several investigators;11,12 therefore, Shemesh and his colleagues13 designed a study to evaluate whether the CAC score can help to identify patients with hypertension and DM who might be at low or moderate rather than high CV risk.

Baseline CAC measurements were obtained in 423 patients who were free of CV disease and were followed for a total of 3 years. Of this group, 268 patients were included in a 15-year, long-term follow-up. The rate of CV events was greater in patients with DM with CAC than in those without (15% vs 7% after 3 years and 52% vs 32% after 15 years). Subjects with DM and without CAC had a significantly better outcome than those with DM and CAC. The authors concluded that CAC measurements for the diagnosis of subclinical coronary atherosclerosis can be used to reclassify the CV risk of patients with hypertension and DM and might contribute to future strategies for preventive treatment.

Commentary

Shemesh et al were able to stratify hypertensive diabetic patients into high- and low-risk CV groups after both short- and long-term follow-up periods based on the presence or absence of CAC. The absence of CAC indicated a more favorable prognosis. In fact, the investigators for the Society of Heart Prevention and Education (SHAPE) have recommended that diabetic patients without CAC be considered to have a moderate rather than a high CHD risk and should therefore receive less-intensive lipid-lowering therapy than currently recommended. The Shemesh study supports such an approach; however, the question of whether asymptomatic diabetic patients should have their treatment intensity diminished solely because of the presence or absence of subclinical atherosclerosis as measured only by the CAC score has yet to be determined. It must be carefully recognized that soft tissue, noncalcified coronary arterial plaque rather than CAC may end up being the earliest marker of subclinical atherosclerosis. This marker was not measured in the Shemesh study because the CAC scores were generated using dual-detector spiral CT, which measures CAC scores and is not capable of accurately evaluating the presence or the character of plaque in the coronary arteries. The occurrence of noncalcified coronary artery plaque in a diabetic patient, even in the absence of an elevated CAC score, may require a recommendation of intensive lipid-lowering therapy and, therefore, the risk category of such a patient should not be reduced to the moderate risk category until adequate clinical trials relating noncalcified plaque to CAC scores and clinical outcomes have been performed.

For the time being, I would recommend that CAC scores be obtained in diabetic patients but would not recommend that the risk category depend on those scores only. Studies of noncalcified soft tissue plaquing as measured by 64-slice CT, which are now in progress, will aid in stratifying cardiovascular risk in these patients. Therefore, all diabetic patients should be considered at high risk for developing CAD whether they have an elevated CAC score or not.

References

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10. Shemesh J, et al. Ordinal scoring of coronary artery calcifications on low-dose CT scans of the chest is predictive of death from cardiovascular disease. Radiology 2010;257:541-548.

11. Bulugahapitiya U, et al. Is diabetes a coronary risk equivalent? Systematic review and meta-analysis. Diabet Med 2009;26: 142-148.

12. Evans JM, et al. Comparison of cardiovascular risk between patients with type II diabetes and those who had a myocardial infarction: Cross-sectional and cohort studies. BMJ 2002; 324:939-942.

13. Shemesh J, et al. Relation of coronary artery calcium to cardiovascular risk in patients with combined diabetes mellitus and systemic hypertension. Am J Cardiol 2012;100:844-850.

14. Naghavi M, et al. From vulnerable plaque to vulnerable patient – part III: Executive summary of the Screening for Heart Attack Prevention and Education (SHAPE) Task Force reports. Am J Cardiol 2006;98:2H-15H.