Context: Data are sparse regarding the prevalence, incidence, and independent prognostic value of minor and/or major electrocardiographic (ECG) abnormalities in asymptomatic postmenopausal women. There is no information on the effect, if any, of hormonal treatment on the prognostic value of the ECG. Objective: To examine association of minor and major baseline and incident ECG abnormalities with long-term cardiovascular morbidity and mortality. Design, Setting, and Participants: Post-hoc analysis of the estrogen plus progestin component of the Women's Health Initiative study, a randomized controlled primary prevention trial of 14 749 postmenopausal asymptomatic women with intact uterus who received 1 daily tablet containing 0.625 mg of oral conjugated equine estrogen and 2.5 mg of medroxyprogesterone acetate or a matching placebo. Participants were enrolled from 1993 to 1998, and the estrogen plus progestin trial was stopped on July 7, 2002. Main Outcome Measures: The Novacode criteria were used to define minor, major, and incident ECG abnormalities. Cardiovascular end points included incident coronary heart disease (CHD) and cardiovascular disease (CVD) events. Results: Among women with absent (n=9744), minor (n=4095), and major (n=910) ECG abnormalities, there were 118, 91, and 37 incident CHD events, respectively. The incident annual CHD event rates per 10 000 women with absent, minor, or major ECG abnormalities were 21 (95% confidence interval [CI], 18-26), 40 (95% CI, 32-49), and 75 (95% CI, 54-104), respectively. After 3 years of follow-up, 5% of women who had normal ECG at baseline developed new ECG abnormalities with an annual CHD event rate of 85 (95% CI, 44-164) per 10 000 women. The adjusted hazard ratios for CHD events were 1.55 (95% CI, 1.14-2.11) for minor baseline, 3.01 (95% CI, 2.03-4.46) for major baseline, and 2.60 (95% CI, 1.08-6.27) for incident ECG abnormalities. There were no significant interactions between hormone treatment assignment and ECG abnormalities for risk prediction of cardiovascular end points. For prediction of CHD events, the addition of ECG findings to the Framingham risk score increased from 0.69 to 0.74 the area under the receiver operating characteristic curve. Similar findings were found for incident CVD events. Conclusions: Among asymptomatic postmenopausal women, clinically relevant baseline and incident ECG abnormalities are independently associated with increased risk of cardiovascular events and mortality, and the information is incremental to the established method of risk stratification. Trial Registration: clinicaltrials.gov Identifier: NCT00000611.
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