Friday April 3 2009
The study did not assess patient healthcare following surgery
"People in deprived areas of England are more likely to die after heart surgery than those in richer areas", The Mirror reported. It said that a study of 45,000 patients found that poorer people had a higher risk of dying, even after risk factors such as diabetes and obesity were taken into account.
The research behind the story found that the greater the social deprivation, the greater the risk of death in the five years after surgery. Even when risk factors associated with social deprivation were taken into account, such as smoking, higher BMI and diabetes, poverty remained a significant independent risk factor.
These findings do not mean that people living in more deprived areas of the country receive poorer post-operative care than people in more affluent areas. The study did not assess healthcare after surgery, and socioeconomic circumstances influence mortality in many different ways.
The researchers advise that the only way to narrow the gap in health between the rich and poor is to deal with the root causes early in life, and throughout life. This includes decent education, adequate housing and employment opportunities. They say that “health will follow”.
Where did the story come from?
The research was carried out by D. Pagano, consultant in cardiothoracic surgery, from Queen Elizabeth Hospital, Birmingham, and colleagues from universities and hospitals around the UK. The study was published in the peer-reviewed British Medical Journal.
What kind of scientific study was this?
The objective of this modelling study was to assess the effects of social deprivation on survival after cardiac surgery, and how this was influenced by potentially modifiable risk factors.
The study collected information on the outcomes of 44,902 people (73% male) in the UK who had heart surgery between 1997 and 2007. The data was obtained from two cardiac surgical databases, which have clinical information on all adults having cardiac surgery in Birmingham and the north west of England. The surgical procedures were carried out by 51 surgeons at five different hospitals. Data was collected when patients were admitted to hospital.
The researchers excluded patients who were undergoing certain high-risk procedures (e.g. surgery where it was necessary to stop the heart, heart transplants, surgery for chest trauma, and surgery for a developed ventricular septal defect). Surgical procedures that were included were coronary artery bypass graft (CABG), heart valve repair or replacement, atrial fibrillation ablation, removal of left ventricular aneurysm, repair of atrial septal defect, and closure of foramen ovale.
The patients’ social deprivation was determined from postcodes, and scores were given based on the 2001 census data. These scores - Carstairs scores - combine four census variables: unemployment, overcrowding, car ownership and low social class. Scores range from the least deprived (-5.71) to most deprived (21.39). Patients were also grouped depending on whether they were smokers (current, ex, or never) and according to body mass index. The researchers kept track of patients using the central cardiac audit database (linked to the Office for National Statistics). They looked at death rates while still in hospital, and survival rates following hospital discharge.
Statistical analyses were used to examine whether social deprivation (the Carstairs score grouped into quarters) predicted mortality within hospital and during follow-up. The researchers took into account (adjusted for) confounding factors associated with social deprivation that can influence mortality, such as smoking, BMI and diabetes. They also looked at the person’s EuroSCORE, which is a cardiac risk assessment score that takes into account factors such as age, sex and heart function and contraction.
What were the results of the study?
Of the 44,902 people having cardiac surgery, 16.4% of them were diabetic (type 1 or 2) and 53.5% had hypertension. At the time of surgery, 21.9% were current smokers, 48.4% were ex-smokers and 29.8% had never smoked. Average BMI was 27kg/m2, average EuroScore was four, and Carstairs deprivation score was -0.54.
Of the sample, 3.3% (1,461 people) died before discharge from hospital. Various factors were associated with in-hospital mortality, including type of surgery (six different types of surgery were associated with different risk; the more complex surgery had the greatest risk). Other hospital mortality factors were EuroSCORE and social deprivation (each point score increase on the Carstairs score increased risk of death by 2.9%). Over an average post-surgery follow-up of 5.2 years, 12.4% of the sample (5,563 people) died.
Each point score in social deprivation increased the risk of death by 2.4% (hazard ratio 1.024, 95% confidence interval 1.015 to 1.033). Having diabetes increased the risk of death during follow-up by 30.5%. Being a current smoker increased risk by 29.4%, while being an ex-smoker increased it by 24.5%. Adjusting for smoking, BMI and diabetes (which were found to be associated with social deprivation score) reduced the increased risk of death with each point increase in social deprivation from 2.4% to 1.7%.
What interpretations did the researchers draw from these results?
The researchers concluded that smoking, extremes of BMI, and diabetes (i.e. potentially modifiable risk factors associated with social deprivation) are responsible for a significant reduction in survival after surgery. However, even after taking these variables into account, social deprivation remains a significant independent predictor of increased risk of mortality.
What does the NHS Knowledge Service make of this study?
This is a valuable and well-conducted study. It has demonstrated that social deprivation is associated with a small increase in the risk of death. Although smoking, BMI and diabetes reduced this risk, social deprivation remained a significant independent risk factor for death following cardiac surgery (1.7% increased risk). There are a few points to note:
- Although this is a very large sample, it only assessed the outcomes of cardiac surgery in the north west region. Other areas of the UK may have different patterns.
- Limited information was available on other medical comorbidity aside from smoking status, diabetes and BMI. These three factors all had significant associations with both risk of death and social deprivation. It is possible that other unmeasured health and lifestyle factors could also be associated with both social deprivation and risk of mortality, and if they had been adjusted for in the analyses they may have further reduced the significance of social deprivation itself as a risk factor (i.e. adjusting for the three factors of BMI, smoking and diabetes had already reduced risk size from 2.4 to 1.7%).
- The reported data does not include actual causes of death, which would be useful in that it allows analysis between individual causes and risk factors.
- As the researchers say, the Carstairs deprivation score is based on postcode only and district of residence. As such, it may not always represent social affluence at the individual level.
- The data was obtained from several different databases, so there may be some inherent inaccuracies in the entered data. Additionally, the available data may have been quite limited and generalised. For example, smoking only assesses habit at a single point in time but does not indicate how often patients smoked, or for how long, or whether they continued smoking after their operations.
- On reading the news stories, this study may be incorrectly interpreted to mean that people living in more deprived areas of the country receive poorer post-operative care than people in more affluent areas. However, there are many mechanisms by which socioeconomic differences can influence mortality. Access to services, post-operative contact with medical professionals and subsequent healthcare during the follow-up period were not assessed in this study.
Whatever the reasons for this demonstrated link between social deprivation and post-cardiac-surgery mortality, inequalities in health across society is an important public health concern that requires attention.