Abstract 15: Change in Physical Activity and Sitting Time After Myocardial Infarction and Mortality Among Postmenopausal Women in the Women’s Health Initiative-Observational Study

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Introduction: The natural history of myocardial infarction in women is different than in men. Evidence related to change in physical activity (PA) or sitting time (ST) after first myocardial infarction (MI) and the association with subsequent mortality in women is sparse.Hypothesis: We hypothesized that women who increased or maintained high PA levels (>7.5 MET-hrs/wk ) following first MI would have lower subsequent risk of all-cause, coronary heart disease (CHD) and cardiovascular disease (CVD) mortality compared to women who remained inactive. We also hypothesized that women who decreased or maintained low levels of ST (<7 hrs/d) following first MI would have lower risk of mortality compared to women who maintained high amounts of ST.Methods: We conducted a prospective analysis among postmenopausal women who experienced a confirmed post-baseline incident MI in the Women’s Health Initiative-Observational Study. The analysis included n = 877 women with PA and n = 514 women with ST assessed both prior to and after the MI. Recreational PA was self-reported at baseline and annually through year 8. ST was self-reported at baseline, year 3, and year 6. Change in PA and ST was calculated from time points immediately before and after MI. Change in PA and ST was assessed continuously and categorically. Categories for change in PA were: (1) active, maintained ≥ 7.5 MET-hrs/wk (equivalent to meeting current PA guidelines); (2) increased from <7.5 to >7.5 MET-hrs/wk; (3) decreased from >7.5 to <7.5 MET-hrs/wk; and (4) inactive, maintained <7.5 MET-hrs/wk. Categories for change in ST were: (1) maintained >7 hrs/d; (2) increased from <7 to >7 hrs/d; (3) decreased >7 to <7 hrs/d; and (4) maintained <7 hrs/d. The primary outcomes were all-cause, CHD and CVD mortality. Multivariable Cox proportional hazard models estimated hazard ratios (HR) and 95% confidence intervals (CI) adjusted for CVD risk factors, including congestive heart failure.Results: Compared to women who remained inactive (< 7.5 MET-hrs/wk) following MI, the multivariable-adjusted HR’s of all-cause mortality were: 0.58 (0.37-0.90) for women who had been active and decreased physical activity; 0.37 (0.20-0.60) for women who had been inactive and increased activity to ≥ 7.5 MET-hrs/wk; and 0.50 (0.36-0.70) for women who remained active. Results were similar for CHD & CVD mortality. In contrast, all-cause mortality did not differ by change in sitting following MI when examined categorically. Nonetheless, when examined continuously, a 1 hour/day increase in sitting time pre- to post-MI was associated with a 9% increased risk of all-cause mortality (HR=1.09, 95% CI: 1.03-1.15).Conclusions: Results suggest that increasing or maintaining physical activity and limiting sitting following a first MI may be important strategies for decreasing mortality in postmenopausal women.

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