Diabetes and Risk of death from coronary events

Diabetes Mellitus and Mortality after Acute Coronary Syndrome as a First or Recurrent Cardiovascular Event
Original source: PLoS ONE Vol. 3, No. 10
Authors: Richard M. Cubbon, Afroze Abbas, Stephen B. Wheatcroft, Niamh Kilcullen, Raj Das, Christine Morrell, Julian H. Barth, Mark T. Kearney (corresponding author), Alistair S. Hall for the EMMACE-2 investigators
Publication date: 22 October 2008
DOI (digital document ID): 10.1371/journal.pone.0003483
Requires subscription? No
Publicly-available abstract: Yes

Synopsis:
Diabetes has been associated with problems recovering from, and with higher risk of death from, acute coronary syndrome. The investigators were looking to find whether this increased risk was true for all persons with diabetes, or only for those persons with diabetes who already had cardiovascular disease, compared to people without diabetes (with, or without, diagnosed cardiovascular disease). The investigators wondered whether cardiovascular disease is diagnosed earlier in people with diabetes than in the general population, and if that early diagnosis, plus aggressive preventative treatment, reduced the risk of dying from acute coronary syndrome.

For the purposes of the study, "Acute Coronary Syndrome" covered unstable angina or myocardial infarction (heart attack). "Cardiovascular Disease" was devined as myocardial infarction, angina, stroke, peripheral vascular disease, or coronary revascularization (either the heart's circulatory system rerouting itself, or the need for stents, bypasses, or other surgical techniques to open or replace blocked blood vessels). Note that by these definitions, "acute coronary syndrome" is a subset of "cardiovascular disease".

The researchers looked at the data collected in the EMMACE-II observational study in 2003, which tracked just under 2500 patients. The investigators used the patients' previous medical records to split the patients into four groups: those without diabetes or previously-diagnosed cardiovascular disease; those without diabetes, but who had existing cardiovascular disease; those with diabetes but without a history of cardiovascular disease; and those with both diabetes and a history of cardiovascular disease. The data from these four groups were analyzed separately and compared.

The results showed that while patients with diabetes had an overall increased risk of death from acute coronary syndrome, the rates of death of patients with no history of cardiovascular disease were approximately the same, regardless of whether or not they had diabetes.

After adjusting for age and gender, there was still an increased risk of death for patients with diabetes and a history of cardiovascular disease over patients from the other three groups; however, when the results were adjusted for levels of Troponin I -- which was used to indicate how much of the heart muscle had died due to cardiovascular disease, the correlation between mortality and diabetes disappeared. This lack of correlation remained even when the investigators broadened or narrowed the definition of cardiovascular disease used in their analysis.

These findings suggest that the risk of dying from acute coronary syndrome may be related to the degree to which the heart's blood vessels have been blocked, and that the reduced degree of blockage in patients with diabetes, but no history of cardiovascular disease, may be related to aggressive preventative treatment that is not routinely offered to people without diabetes.

Reliability:
The authors are from accredited medical institutions and the research is published in a peer-reviewed journal. The size of the study is large enough to show potential trends and suggest directions for further research. The authors note limitations of the study include the absence of several key risk indicators (such as albuminuria -- protein in the urine -- and obesity) and details of any preventative therapy the patients may have received. They also note that patients with a history of previous cardiovascular disease are less likely to receive prescriptions for preventative drugs (such as statins and ACE inhibitors) than patients being discharged after their first acute coronary event, and because this is counterintuitive to standard practice, understanding the reasons for this difference would also help to quantify the differences in risk.

Practical Applications:
Understanding the true origins of the risks of death from acute coronary syndrome can help our doctors better treat us and help us reduce those risks to the greatest degree possible.

For further reading:
The British Cardiac Society Working Group definition of myocardial infarction: implications for practice -- abstract describing the EMMACE-II study.

This synopsis was based on the entire article.