Association of High-Density Calcified 1K Plaque With Risk of Acute Coronary Syndrome

This case-control cohort study analyzes patients with suspected coronary atherosclerosis and control patients to identify the factors associated with higher or lower risks for adverse cardiovascular events and acute coronary syndrome. Key PointsQuestionIs the density of coronary calcified plaque associated with future development of acute coronary syndrome? FindingsIn this case-control study of 189 patients who experienced vs 189 control individuals who did not experience an acute coronary syndrome after baseline coronary computed tomography angiography imaging, the volume of plaque with more than 1000 Hounsfield unit (termed 1K plaque) was associated with lower risk for acute coronary syndrome. The specific acute coronary syndrome precursor culprit lesion had less 1K plaque compared with the most stenotic lesion in control individuals. MeaningThis study's findings suggest that 1K plaque detected by coronary computed tomography angiography is associated with lower risk of future occurrence of acute coronary syndrome. ImportancePlaque morphologic measures on coronary computed tomography angiography (CCTA) have been associated with future acute coronary syndrome (ACS). However, the evolution of calcified coronary plaques by noninvasive imaging is not known. ObjectiveTo ascertain whether the increasing density in calcified coronary plaque is associated with risk for ACS. Design, Setting, and ParticipantsThis multicenter case-control cohort study included individuals enrolled in ICONIC (Incident Coronary Syndromes Identified by Computed Tomography), a nested case-control study of patients drawn from the CONFIRM (Coronary CT Angiography Evaluation for Clinical Outcomes: An International Multicenter) registry, which included 13 study sites in 8 countries. Patients who experienced core laboratory-verified ACS after baseline CCTA (n=189) and control individuals who did not experience ACS after baseline CCTA (n=189) were included. Patients and controls were matched 1:1 by propensity scores for age; male sex; presence of hypertension, hyperlipidemia, and diabetes; family history of premature coronary artery disease (CAD); current smoking status; and CAD severity. Data were analyzed from November 2018 to March 2019. ExposuresWhole-heart atherosclerotic plaque volume was quantitated from all coronary vessels and their branches. For patients who underwent invasive angiography at the time of ACS, culprit lesions were coregistered to baseline CCTA lesions by a blinded independent reader. Low-density plaque was defined as having less than 130 Hounsfield units (HU); calcified plaque, as having more than 350 HU and subcategorized on a voxel-level basis into 3 strata: 351 to 700 HU, 701 to 1000 HU, and more than 1000 HU (termed 1K plaque). Main Outcomes and MeasuresAssociation between calcium density and future ACS risk. ResultsA total of 189 patients and 189 matched controls (mean [SD] age of 59.9[9.8] years; 247 [65.3%] were male) were included in the analysis and were monitored during a mean (SD) follow-up period of 3.9 (2.5) years. The overall mean (SD) calcified plaque volume (>350 HU) was similar between patients and controls (76.4 [101.6] mm(3) vs 99.0 [156.1] mm(3); P=.32), but patients who experienced ACS exhibited less 1K plaque (>1000 HU) compared with controls (3.9 [8.3] mm(3) vs 9.4 [23.2] mm(3); P=.02). Individuals within the highest quartile of 1K plaque exhibited less low-density plaque, as a percentage of total plaque, when compared with patients within the lower 3 quartiles (12.6% [10.4%] vs 24.9% [20.6%]; P<.001). For 93 culprit precursor lesions detected by CCTA, the volume of 1K plaque was lower compared with the maximally stenotic lesion in controls (2.6 [7.2] mm(3) vs 7.6 [20.3] mm(3); P=.01). The per-patient and per-lesion results were similar between the 2 groups when restricted to myocardial infarction cases. Conclusions and RelevanceResults of this study suggest that, on a per-patient and per-lesion basis, 1K plaque was associated with a lower risk for future ACS and that measurement of 1K plaque may improve risk stratification beyond plaque burden.