Association of socioeconomic status with functional capacity, heart rate recovery, and all-cause mortality

Abstract

Context: Lower socioeconomic status (SES) confers heightened cardiovascular risk and mortality, although the mediating pathways are unclear.

Objective: To evaluate the extent to which exercise physiologic characteristics account for the association between lower SES and mortality.

Design, setting, and participants: Prospective cohort study of 30 043 consecutive patients living in 7 counties in northeast Ohio referred between 1990 and 2002 for symptom-limited stress testing for evaluation of known or suspected coronary artery disease. Follow-up for mortality continued through February 2004.

Main outcome measures: Estimated functional capacity in metabolic equivalents and heart rate recovery, physiologic characteristics that are determined directly from exercise; testing and all-cause mortality during a median follow-up of 6.5 years.

Results: Multivariable models adjusting for demographics, insurance status, smoking status, and clinical confounders demonstrated a strong association between a composite SES score based on census block data and functional capacity (adjusted odds ratio comparing 25th with 75th percentile values, 1.72; 95% confidence interval [CI], 1.56-1.89; P<.001) as well as heart rate recovery (adjusted odds ratio comparing 25th with 75th percentile values, 1.18; 95% CI, 1.07-1.30; P<.001). There were 2174 deaths, with mortality risk increasing from 5% to 10% as SES decreased by quartile (P<.001). Cox proportional hazards models that included all confounding variables except exercise physiologic characteristics demonstrated increased mortality as SES decreased (adjusted hazard ratio comparing 25th with 75th percentile values, 1.32; 95% CI, 1.22-1.42; P<.001). After further adding functional capacity and heart rate recovery, the magnitude of this relationship was reduced (comparing 25th with 75th percentile values; adjusted hazard ratio, 1.17; 95% CI, 1.08-1.26; P<.001), with these variables explaining 47% of the association.

Conclusions: Impaired functional capacity and abnormal heart rate recovery were strongly associated with lower SES and accounted for a major proportion of the correlation between SES and mortality. Efforts to modify these clinical features among patients with low SES may narrow disparities in mortality.