Socioeconomic status and out-of-hospital cardiac arrest

Abstract

Background: Out-of-hospital cardiac arrest (OHCA) is a common cause of death. Around 6000 people in Sweden suffer OHCA each year and only about 10% survive. Historically, the focus of OHCA research has been on different treatments such as improved cardiopulmonary resuscitation (CPR) and early defibrillation. Less is known about how underlying risk factors such as socioeconomic status (SES) affect both the incidence and the chance of surviving an OHCA.

Methods: The primary data source for this thesis was the Swedish Register of Cardiopulmonary Resuscitation (SRCR). Study I and Study II included consecutive cases of EMS-treated OHCAs in the Stockholm Region between the years 2006–2015 (Study I) and 2006–2017 (Study II). For these two studies the OHCAs were geocoded and linked to area-level SES data from Statistics Sweden. In Study III and Study IV SRCR OHCA data from the whole of Sweden for the years 2010–2017 were used. Data were linked to individual-level socioeconomic variables such as disposable household income and educational level from Statistics Sweden, comorbidity data from the National Patient Register and medication data from the Swedish Prescribed Drug Register.

Specific aims and results: The aim of Study I was to investigate if socioeconomic characteristics in the area of residence affect the chance of survival after out-of-hospital cardiac arrest. A total of 7431 OHCAs were included in the study. The results suggested a significant association between a higher proportion of university-educated people and 30-day survival. Compared with patients in the lowest educational quintile, the highest quintile showed an adjusted odds ratio (OR) of 1.70 (95% CI=1.15 to 2.51). No significant relationship was seen for area-level income when adjusted for education. The aim of Study II was to investigate the association between area-level SES and the incidence of OHCA, and to investigate if this relationship is dependent on age. A total of 10 574 OHCAs in the Stockholm Region were included in the study. The OHCAs were distributed over 1349 areas which represented the main unit of analysis. Areas characterized by high SES showed an incidence rate ratio (IRR) of 0.56 (95% CI=0.45–0.70) among persons in the age group 0–44. The corresponding number for persons in the 45–64 age group was 0.53 (95% CI=0.45–0.62) and it was 0.59 (0.49–0.0) among persons in the 65–74 age group. In the two oldest age groups (75–84 and 85+) there was no significant association between area-level SES and the incidence of OHCA. The aim of Study III was to examine how individual-level disposable income and educational level is related to 30-day survival following an OHCA. A total of 31 489 OHCAs were included in the study. In the main model, disposable income level followed a gradientlike increase in chance of survival, with the highest estimate in the highest income quintile (OR = 1.89, 95% CI = 1.64–2.17). This relationship remained after adjusting for comorbidity resuscitation factors and initial rhythm. As regards educational level, the highest OR for 30- day survival was found among persons with four or more years of post-secondary education (OR 1.62, 95% CI=1.36–1.92). The aim of Study IV was to investigate the relationship between disposable income and the chance of having a shockable initial rhythm. A total of 18 099 witnessed OHCAs were included in the study. In the low-income tercile, the proportion with shockable rhythm was 30.2%, compared with 51.4% in the high-income tercile when the EMS response time was less than five minutes. The corresponding numbers were 15.9% vs. 27.6% when the EMS response time was more than 20 minutes. In adjusted logistic regression analyses (using restricted cubic splines) the relationship between income and the probability of shockable initial rhythm followed an S-shaped curve, with a small increase in the first income tercile, a steep increase in the second tercile, that levelled out in the third income tercile. This relationship was seen regardless of potential confounders, comorbidities, cardiac-arrest characteristics and previous medication.

Conclusions: The current studies confirm associations between SES, incidence of OHCA, and survival following an OHCA. The results from Study I suggest that individuals living in areas with a higher proportion of university-educated people have a higher probability of surviving to 30 days following an OHCA. In Study II, areas characterized by low SES showed a higher incidence of OHCA. This relationship, however, was dependent on age, and the SESincidence relationship disappeared among people over 75 years of age. In Study III both individual-level income and education were associated with the probability of 30-day survival after OHCA. In Study IV, income was associated with the probability of having a shockable initial rhythm. Initial rhythm may work as a mediator in the relationship between socioeconomic status and survival after OHCA.