In people with diabetes, atherosclerosis is accentuated. There is an increased propensity to vascular injury due to enhanced vasoconstriction and hyperglycaemia. In addition to the usual risk factors there are two further factors that are specific to diabetes: hyperglycaemia and hyperinsulinemia.

• Hyperglycaemia caused by insulin resistance in Type 2 diabetes: Insulin resistance can be defined as the inability of insulin to produce its usual biologic effects at concentrations that are effective in normal subjects, resulting in an increase in blood glucose. The net effects are seen on the liver and peripheral tissues. Elevated glucose concentrations contribute to the development of three conditions that increase the risk of heart disease in people with diabetes: high blood pressure, abnormal lipid profiles and changes in the inflammatory response, which can lead to damage of the blood vessels.
  
  

• Hyperinsulinemia: It is possible that high levels of insulin stimulate proliferation, migration, cholesterol synthesis and binding of low-density lipoprotein (LDL) in vascular smooth muscle cells, leading to arterial wall thickening and atheromatous lesions. Hyperinsulinemia may also raise arterial blood pressure, by stimulating sympathetic nervous system activity, promoting renal sodium reabsorption and inducing vascular smooth muscle hypertrophy. Atherogenic changes in blood lipids and blood coagulability are also linked to hyperinsulinemia.
  
  

The Framingham study showed the risk of CHD was doubled in men with diabetes and tripled in women with diabetes. [Kannel and McGee, 1979a; Kannel and McGee, 1979b] The frequency of cardiovascular disease in the diabetic population is related to that in the background population. [Jay and Betteridge, 1994] Cardiovascular deaths predominate in those who have had diabetes for more than 30 years or were diagnosed after the age of 40 years (Figure 1). [Marks and Krall, 1971]

Figure 1. Percentage of diabetic deaths due to cardiac causes. [Jay and Betteridge, 1994] Enlarge

In addition to people with diabetes having a higher risk of heart disease, they also have worse outcomes. There is evidence that CHD progresses more rapidly in subjects with diabetes and that the lesions are more extensive, severe and run a more aggressive course. The presence of more severe and diffuse atheroma at angiography may also reflect a relative delay in diagnosing people with diabetes with this problem. [Gray and Yudkin, 1997]

Acute myocardial infarction also runs a more complicated course in people with diabetes and is associated with twice the mortality rate of that in the general population. [Yudkin and Hendra, 1992] A fivefold increase in the risk of heart failure and cardiogenic shock has been observed in people with diabetes, and dyspnea may be the only symptom. [Kannel, 1978]

People with diabetes have significantly reduced short- and long-term survival in comparison to the healthy population, because the patients have more progressive disease, even with surgical intervention. [Herlitz, 1988]

It is important in all patients with signs of CHD to prevent any further disease progression, but the aggressive course of the disease in people with diabetes means these patients require even more intensive therapy.

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