The investigators of 16 (of 20 eligible) studies provided data for the analysis (24,955 men and 23,339 women). The median duration of follow up was between 3 and 16.7 years; more than half of the studies were followed up for more than 10 years. Baseline data for ABI and the 10-year incidence of CHD predicted by the FRS are given in the paper. There was considerable variation in annual rates of deaths between the studies.
During 480,325 person-years of follow up the HR for death (ABI compared to reference standard level) when plotted by ABI category showed a reverse J-shaped distribution. The HR or risk of death increased with each of the six decreasing categories of ABI below the standard level (1.11 to 1.20) and was also increased for the category >1.4. These results were observed for both men and women, and similar patterns of results were shown for cardiovascular mortality and major coronary events. (The number of participants varied considerably between categories and in some categories the numbers of events were few). The HRs for TM, CM and MCE showed an increased risk of death in the generally accepted "at risk" range (<0.90) compared to "normal" (1.10 to 1.40) ABI for both men and women. HRs remained high after adjusting for FRS in men and women. A low ABI (≤90) almost doubled the risk of 10-year total mortality, cardiovascular mortality and major coronary events compared with overall rates in all FRS categories.
The inclusion of the ABI in cardiovascular risk stratification alongside the FRS would mean that reclassification of the risk category and modified treatment recommendations would be necessary in approximately 19 per cent of men and 36 per cent of women.