Commentary: Weighing risk/benefit ratio of CAC scoring
CAC scoring via multislice CT is a noninvasive, patient-friendly test that can be available at low cost to the patient and the healthcare system. Like any diagnostic testing procedure, radiation exposure is evaluated for risk-benefit ratio to the patient.
For approximately 50 percent of the population, a myocardial infarction is the first presenting symptom of heart disease. Additionally, it has been published that over 40 percent of first infarction patients will not survive. To reduce cardiovascular disease mortality, we must utilize modalities that facilitate early detection of the disease process in appropriate populations.
A recent paper by Kim et al, which evaluated cancer risk among CAC patients using a computer modeling program, showed a wide radiation dose variation and, according to the authors, may have overestimated radiation doses for CAC scoring and the recommended frequency of CAC testing (Arch Intern Med 2009;169:1188-1194). The methodology and calculations have led to controversial findings and a potentially skewed risk-benefit ratio.
The Society for Heart Attack Prevention and Eradication (SHAPE) published recommendations for CAC scoring in 2006 (Am J Cardiology 2006;98:2-15). The recommendations suggest CAC screening for males aged 45-75, females 55-75 and re-test intervals of five years as used by the above authors. However, the re-test recommendation of every five years was limited to patients having a zero CAC score.
The computer modeling paper estimated lifetime radiation exposure based upon a model of CAC re-testing every five years for the life of the patient. The methodology would lead to excessive radiation estimation as widely reported data show that only 40 percent of the clinically indicated population will have a negative (0) CAC result. The remaining 60 percent of patients will have varying degrees of coronary artery disease and are not recommended to be re-scanned every five years as factored into the published cancer risk paper. The majority of patients having a positive CAC study will be medically managed by their healthcare provider to restrict progression of the disease. Those with significant CAC (greater than 400) will be referred to a cardiologist for appropriately indicated diagnostic testing and potential medical intervention.
A second factor leading to a potentially inflated cancer risk were the CAC radiation dose estimations. The authors disclosed that there was an observed 10-fold variance in effective dose estimations (range: 0.8-10.5 mSv), which were highly dependent upon CAC protocol and scanning equipment. A median dose of 2.5 mSv was used for mathematical projections.
Data from other published sources as well as our CCTA and CAC registries have found the effective radiation dose for CAC scoring to consistently range from 0.8-2.9 mSv for sites using 16-slice generation scanners or newer. Our calculated mean CAC effective dose was 1.9 mSv, which is significantly lower than the median value used above. As the authors indicated, CAC protocols and dose reduction strategies have the ability to reduce radiation exposure and should be employed as standardized procedures to reduce risk during CAC testing.
CAC scoring has the ability to reduce incidence of major cardiovascular events and mortality if employed judiciously within a predefined and appropriate asymptomatic population. CAC screening also affords the opportunity to reduce global healthcare expenditures via early detection of this chronic disease and acute event prevention. Lastly, a clinically developed CAC program implementation provides the clinician and CT enterprise a clinically and economically desirable opportunity as we enter the “prevention and early detection era” in healthcare.
Dr. Fine is the president and CEO J & J Medical, a medical knowledge company specializing in heart attack prevention program business development and physician education. He can be reached at firstname.lastname@example.org.