Does Quantifying Epicardial and Intrathoracic Fat With Noncontrast Computed Tomography Improve Risk Stratification Beyond Calcium Scoring Alone?

Study Questions:

Does measurement of epicardial and intrathoracic fat volume add prognostic information to coronary artery calcium (CAC) scoring for assessment of cardiovascular risk?

Methods:

Cardiac computed tomography (CT) scans were performed in consecutive patients presenting to the emergency room with acute chest pain. Only patients with no prior history of coronary artery disease were included in this analysis. CAC scores (CACS) were calculated using the Agaston method. Epicardial fat and intrathoracic fat volumes were semi-automatically calculated. Mean follow-up for the cohort was 3.3 years. The primary outcome of interest was a combined cardiac endpoint of major acute cardiac events (MACE), which included cardiac death, nonfatal myocardial infarction, and unstable angina pectoris.

Results:

A total of 760 patients were included in this study (mean age 54.4 ± 13.7 years, 59% female). Diabetic patients comprised 15% of the population. Average Framingham risk score (FRS) was 8.2 ± 8.2. In the 760 patients, 450 (59.2%) had CACS of 0; 174 (22.9%) had CACS of 1-100; 71 (9.3%) had CACS of 101-400; and 65 (8.6%) had CACS >400. The mean intrathoracic fat volume was 255 ± 132 ml, and 327 patients (43%) had an intrathoracic fat volume of >250 ml. The mean epicardial fat volume was 127 ± 61 ml, and 345 patients (45.4%) had an epicardial fat volume of >125 ml. Forty-five patients (5.9%) had at least one MACE (6 cardiac deaths, 17 nonfatal myocardial infarctions, and 22 with unstable angina) over the follow-up period. Patients who experience MACE were older (64.8 ± 13.9 years vs. 53.7 ± 13.4 years), more likely to be male (60% vs. 40%), had higher FRS (16 vs. 4), and higher CACS (268 vs. 0) compared to patients without MACE (p < 0.01 for all comparisons). Patients who experienced MACE had higher epicardial fat volumes (154 vs. 116 ml) and higher intrathoracic fat volumes (330 vs. 223 ml) compared to patients without MACE. CACS, epicardial fat volume, and intrathoracic fat volume were all independently associated with MACE. CACS were associated with MACE after adjustment for fat volumes (p < 0.0001), whereas epicardial fat volume and intrathoracic fat volume improved the risk model only in patients with CACS >400.

Conclusions:

The investigators concluded that both CACS and fat volumes independently predict risk for MACE in patients with acute chest pain symptoms. Although fat volumes may add prognostic value in patients with CACS >400, CACS is most strongly correlated with outcome.

Perspective:

These data provide evidence that both epicardial fat and intrathoracic fat may be active in increasing the risk for cardiovascular events, particularly among patients with elevated CACS. Whether aggressive risk factor modification would result in reduction of risk related to these fat deposits is not clear.

Clinical Topics: Noninvasive Imaging, Computed Tomography, Nuclear Imaging

Keywords: Myocardial Infarction, Tomography, X-Ray Computed, Calcium


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