There are two major findings of this study. First, in a community-based sample of multiethnic participants free of CVD, there was a weak to moderate unadjusted correlation between PF volume and carotid IMT (r
= 0.27 for CCA-IMT and 0.17 for ICA-IMT, P<0.0001
for both). These correlation coefficients are much less than the correlation coefficient (r
= 0.92, P<0.01
) that has been reported between carotid IMT and cardiac fat depot in a patient-based sample (8
). Such discordant results could be possibly explained by differences in populations studied and also by other methodological issues that warrant highlighting. We used CT measures of PF volume instead of echocardiography measures of PF thickness, which is one of the strengths of our study. Echocardiography is not the optimal technique for quantification of PF; CT is more sensitive and specific (18
). Further, differences in the measurement of what could be defined as pericardial fat could be another factor for differences in the results
The second major finding of this study is that the association between PF and carotid IMT was not independent from markers of overall adiposity or common risk factors for atherosclerosis. In our linear regression models, the association between PF and carotid IMT did not persist after adjusting for BMI, waist circumference or common risk factors for atherosclerosis. Noteworthy, BMI and waist circumference showed statistically significant associations with carotid IMT (especially CCA-IMT) either when combined or not combined with PF in similar regression models. Hence, it is unlikely that undetected collinearity between PF with BMI or waist circumference might have affected the statistical significance of all independent variables including PF, BMI and waist circumference. Nevertheless, we have noticed that the associations between PF, BMI and waist circumference with ICA-IMT were statistically weaker than those associations with CCA-IMT. This could be explained by the known unavoidable increased variability in ICA-IMT ultrasound measures and subsequently dilution of its relationships with the independent variables in our models. Measurement variability for ICA-IMT has been shown to be approximately three times greater than that for CCA-IMT (13
). Anatomical and technical considerations play a major role in these variations. The ICA usually lies deeper in the neck and, at its origin, the walls are not parallel, and it does not lie parallel to the surface of the neck. On the other hand, CCA has straight walls, is superficial, and usually lies parallel to the surface of the skin. The CCA is easier to study, and its IMT measures are more reproducible than that of ICA (20
). For these reasons several studies (6
) used only CCA-IMT as a subclinical marker of atherosclerosis risk. Despite its increased measurement variability, ICA-IMT provides unique biological information as it is more linked to focal atherosclerotic disease such as plaque (20
). It may therefore be that the associations between PF and ICA-IMT are stronger in men compared to women (as noticed in ), because men inherently have more plaques than women of the same mean age. Examining the relations between PF and both CCA-IMT and ICA-IMT is another strength of this study.
We believe that our reported association between PF and atherosclerosis should be interpreted within the context of the mechanisms by which PF could be related to atherosclerosis. A systemic
effect is the only plausible mechanism by which PF could have an effect on carotid IMT. Lack of independent association between PF and carotid IMT, in our study, means that PF might not have an independent systemic
effect on atherosclerosis. On the other hand, additional local (and independent) atherogenic effects of PF on coronary atherosclerosis may exist, given the proximity between PF and coronary arteries. In another analysis from MESA, there was an association between PF and calcified coronary plaque (11
One of the common concerns regarding measures of adiposity (especially PF and BMI) is that these measures might have been biased by body morphometry. For example, individuals with large body surface area would have bigger hearts with more pericardial surface and subsequently more PF than individuals with less body surface area. In the same sense, tall individuals would have higher BMI, not necessary reflecting fat content. Hence, to exclude the possibility that differences in body morphometry did not bias the measures of PF and BMI in our study, which would subsequently bias our results and conclusions, we reran all the PF and BMI models after adjusting for body surface area and height respectively. The results of these additional analyses did not in any way change the conclusions we made regarding the significant but not independent association between PF and carotid IMT (results not shown).
In this multiethnic community-based study, PF is associated with carotid IMT, an association that is not independent from markers of overall adiposity or common risk factors for atherosclerosis. Therefore, PF measures seemed to have little additional value as a risk factor for atherosclerosis, as measured by IMT, beyond BMI and waist circumference.