NEW YORK - Progression of the coronary artery calcification (CAC) score over time predicts the risk of cardiovascular disease, but it performs no better than the most recent CAC score, according to findings from the Cooper Center Longitudinal Study (CCLS).
"I must admit that I expected to find that the change in CAC was going to provide a lot of information about cardiovascular events, and was quite surprised when it didn't add much," Dr. Benjamin D. Levine from Cooper Clinic and University of Texas Southwestern Medical Center, Dallas, Texas told Reuters Health by email. "I was then also surprised when Dr. Andre Paixao, one of our cardiology fellows at the time (now at Emory), suggested that we look at the last CAC score as the best measure for risk attributable to CAC, and he turned out to be right!"
CAC correlates with overall atherosclerotic plaque and predicts incident coronary heart disease (CHD) events, CHD mortality, and total mortality, but only a few studies have evaluated the implications of CAC progression.
Dr. Levine and colleagues used CCLS data from 5,933 participants free of cardiovascular disease (CVD) at baseline to evaluate the relative contributions of baseline CAC score, follow-up CAC score, and CAC progression rates to the risk of incident CVD events.
At baseline, 2,870 (48%) individuals had CAC. These individuals were older, more likely to be on statin therapy, and had higher systolic blood pressure and lower cardiorespiratory fitness, according to the June 29th JACC Cardiovascular Imaging online report.
Individuals with detectable CAC at baseline had significantly higher total CVD event rates than those without detectable CAC (7.70 vs 1.44 per 1,000 person-years, respectively), as well as hard CVD event rates, i.e., CVD death, nonfatal myocardial infarction, or nonfatal atherosclerotic stroke (2.68 vs 1.14 per 1,000 person-years, respectively).
Rates of total CVD and CHD events increased across quartiles of CAC progression, but there was no independent association between CAC progression and CVD outcomes after adjustment for the follow-up CAC score.
"These findings greatly simplify the interpretation of CAC scores over time," Dr. Levine said. "Because it is so difficult to quantify 'change' (a score that goes from 1 to 2 is 100% change, but from 101 to 102 is 1% change), it has been hard for clinicians to wrap their minds around the additional risk information that is contained in follow up scores. Since it is not the calcium we are worried about anyway (calcified plaque generally doesn't rupture - it is the company it keeps that is important), what matters is the overall atherosclerotic burden, as reflected by the absolute CAC score. How fast it changes doesn't matter at all!"
"Don't worry about complicated formulas for quantifying change in CAC," Dr. Levine said. "Just use the latest score to calculate the risk associated with CAC. Now that new calculators are available (and some new ones coming from our work in this space), only the latest CAC score is needed to assess risk."
In an editorial, Dr. Prediman K. Shah from Cedars Sinai Hart Institute in Los Angeles writes, "So change in CAC score may be bad, indifferent, or possibly even good depending on what causes the change: progression of underlying atherosclerosis (potentially bad) versus increased density of calcification indicating a plaque stabilizing response (potentially good)."
Dr. Shah continues. "How to distinguish potential contributors to change in CAC score remains an important and at this time an unanswered question."
"Addition of other variables that incorporate regions of change, change in regional density and other volumetric aspect of CAC change, extracoronary calcification, and epicardial fat volume may improve the value and relevance of change in CAC score," Dr. Shah said. "Further studies are needed to address these issues."
Dr. Joseph Yeboah from Wake Forest Baptist Health, Winston-Salem, North Carolina, who has also researched the association between CAC scores and cardiovascular disease risk, told Reuters Health by email, "This happens to be the first study to show that CAC progression is not informative for CVD risk assessment. At the very best, this study makes the data mixed, which is not surprising given the challenge of using a change in a variable (CAC progression) as a predictor. Some researchers have suggested that CAC density progression instead of CAC score progression may be more appropriate."
"In my opinion, these results will have very little influence on how CAC is used presently for CVD risk assessment," he said. "To my knowledge, there is presently no guideline or recommendation regarding the use of CAC progression for CVD risk assessment. This is because of the inherent challenges in assessing CAC progression and the paucity of data."
"The ACC/AHA guidelines clearly recommend the use of CAC, not CAC progression," Dr. Yeboah concluded. "The take away message here is that physicians should not use CAC progression for CVD risk assessment. More research is needed to fully understand CAC progression."
J Am Coll Cardiol Imag 2016.