Meta-Analysis of Calcium Score and Frequency of Ischemia on MPI
What is the relationship between amount of coronary artery calcium (CAC) and presence of ischemia on stress testing with myocardial perfusion imaging (MPI)?
The authors conducted a meta-analysis of studies investigating the relationship between CAC score and presence of inducible ischemia on MPI. CAC score was divided into four categories: 0, 1-100, 101-399, and ≥400.
The authors identified 20 relevant studies, most of patients with suspected coronary artery disease. The pooled prevalence of ischemia increased with increasing CAC: 6.6% (range 0.0-24.1%) with CAC = 0, 8.5% (range 2.1-50.0) with CAC 1-100, 10.5% range (4.0-63.6%) with CAC 101-399, and 23.6% (range 12.4-57.1) with CAC ≥400. High rates of CAC >0 were seen among both ischemic (86%) and nonischemic scans (72%). However, extensive CAC (≥400) was seen in 53% of ischemic scans and only 25% of nonischemic scans.
Although there is a quantitative relationship between the amount of CAC and the probability of inducible ischemia, there is wide variability across studies. The rate of ischemia was generally low among patients with no CAC.
This very interesting study has several important take home messages: 1) Although ischemia is uncommon in patients with zero CAC, the rates are not negligible with a pooled average of 8.5% of subjects with zero CAC having ischemia, ranging up to 50% in one study. This suggests that in appropriate patients with typical symptoms, a zero calcium score is insufficient to rule out ischemia. 2) Calcium was highly prevalent in both ischemic and nonischemic scans. This suggests that prevention medications are likely to be important in many subjects with nonischemic stress tests. 3) Approximately one in four patients with extensive CAC (≥400) had an ischemic stress test, supporting recommendations to offer stress testing to these patients. This study was challenging in that many of the underlying studies which were analyzed used different categorization schemes for CAC. Furthermore, one could ask the question whether ischemia is the only relevant outcome. Patients who had silent, completed myocardial infarctions could have CAC and fixed perfusion abnormalities (i.e., no inducible ischemic defects). These patients could warrant further investigation and would likely benefit from secondary prevention therapies.
Keywords: Coronary Artery Disease, Diagnostic Imaging, Exercise Test, Myocardial Infarction, Myocardial Ischemia, Myocardial Perfusion Imaging, Plaque, Atherosclerotic, Secondary Prevention
< Back to Listings