It is astonishing to me that, although coronary artery disease is the number one cause of death in the U.S. today, there is no accepted screening test for the disease. Some will argue with this statement, but I emphasize that all current screening for coronary artery disease today is based on screening for risk factors of coronary artery disease.
Dr. Fred Grannis Jr.Such risk factors include diabetes, obesity, hypercholesterolemia, dyslipidemia, and hypertension. But no test screens for coronary artery obstructive lesions.
Coronary artery stress testing is approved only in the setting of symptoms suggestive of ischemia. The closest thing that we have is the CT scan, with special measurement and categorization of calcification in the walls of coronary arteries. Such calcium scores are known to correlate with obstructive lesions.
In an article published recently in the New England Journal of Medicine and reviewed on AuntMinnie.com, researchers from Denmark concluded that CT screening for coronary calcification may not reduce mortality. In the Danish Cardiovascular Screening (DANCAVAS) trial, they found there was no statistically significant difference in mortality between men who were invited to a cardiac screening program that included CT and those who didn't.
There should be no surprise there. Screening in and of itself, unless accompanied by a treatment algorithm that guides interventions to prevent complications and death from the disease in question, will be ineffective. As McGill epidemiologist Dr. Olli Miettinen, PhD, pointed out years ago, CT screening for lung cancer is not "an intervention."
The true intervention is the treatment of early-stage lung cancers diagnosed by CT screening. The benefit of treatment interventions, in terms of long-term cure, is dependent on the quality of the treatment regimen associated with the screening.
For example, survival after treatment of CT-detected lung cancers was substantially higher in the International Early Lung Cancer Action Program (I-ELCAP) study, which utilized a diagnostic and treatment algorithm, than was survival in the National Lung Screening Trial (NLST), which did not.
Accordingly, the value of identification of coronary calcification can only be determined in a study where further workup and/or treatment occurs following a positive test. Such further diagnostic workup and/or treatment does not appear to have taken place in the DANCAVAS study described.
A more informative study might include one in which patients with heavy calcification in proximal coronary arteries went on to stress testing and/or coronary angiography. The important research question is whether survival benefits would be seen when patients with dangerous high-grade obstructions associated with ischemia were identified and treated with angioplasty or coronary artery bypass surgery.
My hypothesis is that substantial survival advantage and mortality reduction of such a CT-based cardiac screening program would be achieved.
Dr. Frederic W. Grannis Jr. is an emeritus clinical professor of thoracic surgery at the City of Hope National Medical Center in Duarte, CA.
The comments and observations expressed here are those of the author and do not necessarily reflect the opinions of AuntMinnie.com.
