Value of Coronary Calcium in Predicting Future Cardiac Events

Abstracts & Commentary

Synopsis: Physicians should continue to risk-stratify and educate their patients by accepted clinical guidelines. The role of advanced testing techniques such as electron beam computerized tomography will almost certainly be defined over the next several years. Sources: Detrano RC, et al. Circulation 1999;99:2633-2638; Pitt B, Rubenfire M. Circulation 1999;99:2610-2612.

Numerous studies have clearly demonstrated that asymptomatic persons with undesirable risk factors benefit from aggressive risk-factor modification. Recently, noninvasive evaluation of coronary calcium by electron beam computerized tomography (EBCT) has been suggested as an effective new approach to risk stratification, especially in high-risk adults (whether symptomatic or asymptomatic).

Detrano and colleagues from the Harbor-UCLA Medical Center recruited 1196 asymptomatic high-coronary-risk subjects who underwent a complete risk-factor assessment and were then studied with EBCT scanning. Coronary calcium was detected by EBCT in 68% of these subjects who were then followed for 41 months. Detrano et al determined that neither risk-factor assessment nor EBCT calcium detection was an accurate event predictor in high-risk asymptomatic adults. The EBCT calcium score did not add significant incremental information to traditional risk factor assessment and Detrano et al conclude that the use of EBCT in clinical screening was not justified at this time.

Comment by Harold L. Karpman, MD, facc, facp

The Harbor-UCLA EBCT facility was one of the first EBCT laboratories in the country. Therefore, the results of this investigation are extremely important because of the broad experience of this facility in the use of EBCT and because of the high volume of patients that they have seen over the years. The results of this study clearly demonstrate that, in high-risk asymptomatic patients, EBCT coronary calcium scores are essentially equivalent in value to traditional risk-factor assessment in identifying individuals who may eventually suffer coronary death and/or infarction from those who will not. Furthermore, coronary calcium assessment with EBCT added no prognostic information beyond that obtained by assessment of standard risk factors. Finally, it should be noted that when using the receiver-operated characteristic (ROC) curve areas calculated from the Framington risk factor model, it would appear that both approaches predicted death or infarction with only fair accuracy.

Advances in our understanding of the pathophysiology of coronary artery disease and plaque rupture hold great promise for improving risk stratification even though the present study clearly demonstrates the failure of the EBCT procedure to add value to standard traditional risk assessment techniques used in identifying asymptomatic patients who are at high risk of developing myocardial infarction and/or death. However, it must be recognized that the Detrano study suffered a number of significant limitations and possible biases. The volunteer subjects were predominantly elderly men with a mean age of 66 ± 8 years who were initially recruited knowing that they were at high risk and, in addition, they were also informed of the results of the initial cardiac fluoroscopy and subject EBCT; therefore, it is likely that many of these patients consulted physicians and received aspirin, HMG-CoA reductase inhibitors, diet instructions, advice to discontinue cigarette smoking, and/or were placed on exercise regimens. Knowing their calcium scores undoubtedly resulted in a positive influence in their risk factor modification behavior that might not have occurred in the case in a high-risk voluntary study population who remained ignorant of their EBCT scores.

Despite the shortcomings of this study, it seems reasonable to conclude that the use of routine EBCT to risk-stratify asymptomatic patients whether high risk or low risk for future risk of ischemic events is not currently justified on a clinical basis pending data from future well-designed, prospective clinical research studies to the contrary. On the other hand, there seems to be little question that EBCT will prove to be of value in both the diagnosis and in designing treatment regimens for patients with coronary artery disease but the exact role of this interesting technology is still being defined. For the time being, physicians should continue to risk-stratify and educate their patients by accepted clinical guidelines and the role of advanced testing techniques such as EBCT will almost certainly be defined over the next several years.

References

1. American Heart Association Annual Report. 1996.

2. Lipid Research Clinics Program. JAMA 1984;251:365-374.

Which of the following statements is not true?

a. Risk-factor assessment was not an accurate event predictor in high-risk asymptomatic adults.

b. EBCT calcium detection was not an accurate event predictor in high-risk asymptomatic adults.

c. The EBCT calcium score added significant incremental information to traditional risk factor assessment.

d. None of the above