Endothelial function in a large community.

To the Editor: We read with interest the study of Benjamin et al1 investigating clinical correlates of flow-mediated vasodilation (FMD) in a large community (The Framingham Heart study) of almost 3000 patients. The authors demonstrated in stepwise multivariable linear regression models that FMD was inversely related to age, systolic blood pressure, body mass index, lipid-lowering medication, and smoking, whereas it was positively associated with female gender, heart rate, and prior walk test. Despite thorough statistical analyses performed in a large cohort, in our opinion some important issues have not been addressed by this study. According to Figure 2 in the article, the mean FMD% of patients with the lowest risk score was 2.8% in men and 4.1% in women, respectively. In an earlier study by the same group,2 mean FMD% in patients with prevalent coronary artery disease (77% men) was 6.7%. Although the discrepancy may be partially explained by different FMD techniques (forearm versus upper arm cuff position), the low FMD values in these patients without cardiovascular disease and a low-risk score are still surprising. It would be interesting to compare the mean FMD% values between the low-risk patients and patients with cardiovascular disease in the present study (8% of women and 18% of men according to Table 1 of the article). This study further challenges the clinical importance of single FMD values in patients with cardiovascular risk factors and/or coronary artery disease. Unfortunately, the authors do not comment on this issue. Additionally, prevalent cardiovascular disease correlated weakly with FMD% in a univariate analysis. In the multivariate model, however, cardiovascular disease was no longer associated with FMD%. We have shown in an earlier study that FMD was not different between patients with and without coronary artery disease.3 Taken together, we feel that the present study1 and our previous study3 support the hypothesis that FMD more accurately reflects risk factor burden than prevalent coronary artery disease.