DISCUSSION
The results of our propensity matched study indicate that in patients
with HF, having a NAHIL >30,000 euros is associated with an
improved prognosis, decreased mortality and hospitalizations. The most
common socioeconomic indicator used in previous studies has been
individual (1), household (30), or neighborhood income (4,
10). However, income may inadequately reflect socioeconomic position,
particularly after retirement. Only a minority of the studies utilizing
income addressed this limitation by examining additional socioeconomic
indicators such as those employed in our study (30-32).
In comparison to previous observational studies (1, 2-7), our study is
characterized by its prospective design and comprehensive collection of
data on a numerous cohort of patients with incident HF, included in the
15 years study period, with a valid echocardiographic study in all of
them. Most of the patients were diagnosed with HF as outpatients, and
they present socio-demographic and clinical characteristics
representative of the habitual clinical practice in this type of
disease. Both the follow-up over time of the variables and the
evaluation of therapeutic compliance have been comprehensive. We set out
to perform PS matching and a rigorous statistical analysis of the
results, adjusting for covariates not considered by previous studies,
that are closely related to SES and prognosis. As SES is a time-varying
exposure, we have performed multivariate analyses considering
time-dependent exposure to SES. Finally and more important, this is the
first study on SES and prognosis of HF including objective measures of
cardiac dysfunction, HFrEF vs. HFpEF.
The observed associations between SES and HF prognosis are not fully
explained by health-related behaviors, lifestyle factors, or traditional
cardiovascular risk factors (32-34). The literature suggests that, the
independent associations of SES with cardiovascular outcomes and
mortality, at least partially reflect the influence of chronic stressors
in daily life, which disproportionately affect persons in low SES groups
(35, 36).These chronic stressors might result in maladaptive physiologic
coping mechanisms and chronic elevations in blood pressure and
inflammation that can lead to physiologic injury of the vasculature and
myocardium (8). Once HF is established, deprived groups face numerous
challenges, including limited access to healthcare (10),
transportation costs, affordability of drug regimens (33), inequalities
in treatment (34), greater co-morbidity precipitating cardiac
decompensation, fewer contacts with primary care (3), and consequently
more reliance on secondary care. Problems are compounded by impaired
health literacy, education, and social support (35), coupled with poor
compliance with medications, diet, and lifestyle restrictions (36).
Further, as in our study, education levels correlate with SES (37),
patients with higher education may have better understanding and
knowledge of their disease process and treatment (38), while patients
with lower education levels are less likely to be adherent to
therapeutic recommendations (39). In addition, lower education level has
been shown to be associated with poor quality of life (40), anxiety
(40), physical and emotional distress (41), and inability to
actively participate in self-care recommendations (42). Higher levels of
education have also been shown to be associated with higher levels of
disease-specific knowledge, healthy lifestyle, and improved outcomes
(43-45).
Limitations. Firstly, there are limitations derived from an
observational study on the habitual clinical practice, which prevent us
from discounting completely any residual factors of confusion not
determined, and any bias in the selection of the patients, that might
explain our results. To reduce the possible influence of these
weaknesses in the design of our study, a PS analysis has been performed,
adjusting for a wide range of covariates. We have no data on the levels
of brain natriuretic peptide (BNP), which constitutes a valuable element
for the diagnosis and prognosis of patients with HF (46, 47). In our
analysis, we used household income rather than total wealth or
education, but adjustment for the educational level, the marital status,
the living status, dependency, number of households, occupational
status, total wealth and properties value, allows us to more
comprehensively capture the cumulative results of SES on cardiovascular
health over the life course in participants (2, 16, 17). We also lack
information about the functional status, presence of anxiety or
depression, the quality of life of our patients (50), and the literacy
of patients or the main care-giver (48). Finally, this is a study
carried out in only one center, and in one specific area of the south of
Spain, with a population uniformly of white race, with medium-low
socioeconomic and educational level, which has universal public health
insurance giving people open, cost-free access to the health system
(visits, tests and medication), thus limiting generalizability.
International geographic variations in event rates has been observed in
studies on HF (49).
Acknowledgements: To the members of the Grupo para la
atención médica integral y continua de Cádiz (GAMIC), without whose
work this paper could not have been written. To Prof. José Almenara for
the performance of the statistical analyses and, to Royston Snart for
his professional help in the translation of the manuscript into English.