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Disposable household income inversely linked to mortality after cardiac surgery
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Patients with more disposable income had significantly lower mortality rates than those with less disposable income in a population-based observational cohort study.
The researchers evaluated data on income, education, marital status, medical history and CV risk factors collected from 100,534 patients who received CABG, valve repair/replacement or both in Sweden between 1999 and 2012. The mean age of the cohort was 67 years (27% women). All-cause mortality was assessed in this population during a mean follow-up of 7.3 years.
During follow-up, 29% of the population died. The mortality rate was 43% in the lowest income quintile, 38% in the second, 30% in the third, 20% in the fourth and 14% in the highest quintile.
Patients with less disposable income were older, more frequently female, and more likely to have CV risk factors including chronic kidney disease, diabetes, prior MI or stroke, HF or chronic obstructive pulmonary disease than those in the highest income quintile.
The researchers observed an inverse association between disposable income and mortality: Compared with the lowest quintile, the researchers calculated an adjusted HR of 0.93 (95% CI, 0.89-0.96) for the second quintile, 0.87 (95% CI, 0.84-0.91) for the third, 0.78 (95% CI, 0.75-0.82) for the fourth and 0.71 (95% CI, 0.67-0.75) for the highest income quintile after 15 years of follow-up. A similar association was observed for mortality within 30 days of surgery, with an adjusted HR of 0.73 (95% CI, 0.62-0.88) for the highest income quintile compared with the lowest.
The link between income level and mortality risk was observed across all evaluated subgroups according to age, sex, education, marital status, procedure type and the year in which the patient received surgery. However, the researchers noted the association was partially attenuated among older and married patients.
In a subset of patients for which information on the cause of death was available, the association was more pronounced for CV-related mortality (HR = 0.53; 95% CI, 0.49-0.57 for highest vs. lowest quintile) than all-cause mortality (HR = 0.64; 95% CI, 0.6-0.69).
The researchers wrote that these findings “are of particular interest because the study was conducted in a population that benefited from universal tax-financed health care.” They noted, however, that they were unable to obtain information on behavioral risk factors such as tobacco use, diet and physical activity, and that residual confounding may have been present in the results.
In a related editorial, David A. Alter, MD, PhD, of the University Health Network-Toronto Rehabilitation Institute, Institute for Clinical Evaluative Sciences, Toronto, also acknowledged the lack of information on risk behaviors and the inability of the study to take several potential confounders into consideration.
“Short of a large natural history study that prospectively tracks [socioeconomic status], behaviors, health status, risk factors and disease longitudinally over time, it is unlikely that researchers would ever be able to temporarily disentangle potential root causes from their downstream disease sequelae,” Alter wrote. “Observational studies using large multilinked registries will never fully elucidate intermediary causal mechanisms and/or the modifiability of [socioeconomic status] outcome gradients.” – by Adam Taliercio
Disclosure: The researchers and Alter report no relevant financial disclosures.
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