#98 Is Diabetes a Coronary Heart Disease Equivalent?

CLINICAL QUESTION

Do patients with diabetes have the same risk of cardiovascular (CV) events as patients with existing coronary heart disease (CHD)?

BOTTOM LINE

Though diabetes does confer an increased risk of CV events, it is not automatically equivalent to having experienced a myocardial infarction (MI) (and thus does not always warrant aggressive pharmacotherapy). CV risk should be predicted, and therapy guided, by taking into account individual risk factors.

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EVIDENCE

Meta-analysis¹ of 13 observational studies (45,108 patients):

Compared with patients with previous MI, diabetic patients have half the risk of CHD.
- Odds ratio 0.56 (95% confidence interval 0.53-0.60).

Danish cohort study² (>150,000 patients):

After adjusting for some cardiac risk factors, socioeconomic status, and CV drugs:
- Diabetics had lower risk of MI or coronary death (hazard ratio 0.63 in men and 0.54 in women) than patients with prior MI.
- Limitations: No adjustment for most traditional risk factors (blood pressure, smoking status, etc.), which would have likely attenuated the association in diabetics further.

US cohort study³ (>160,000 patients): Hazard ratio for fatal or non-fatal CHD event adjusting for traditional CV risk factors vs those without diabetes or CHD:

Diabetes: 1.70 (1.66-1.74);
Diabetes duration >10 years: 2.7 (2.6-2.8);
Prior CHD: 2.76 (2.69-2.85);
Both diabetes and prior CHD: 3.91 (3.78-4.05).

Context:

North American guidelines^4,5 no longer equate diabetes to existing CHD.
Canadian cholesterol guidelines⁴classify diabetics with ≥1 of the following as high-risk patients who may benefit from a statin:
- Age ≥40 years;
- Age ≥30 years and duration of diabetes >15 years; or
- Microvascular disease (nephropathy, neuropathy, retinopathy).
The observational study6 that originally generated the concept of diabetes-CHD equivalence had multiple limitations, including selection bias and being very underpowered.
Presence of diabetes approximately doubles the risk of CV events:^3,7
- Associated risk further increased by longer duration of diabetes,^3,8 increasing HbA1c,⁹ and traditional cardiac risk factors.¹⁰
Most studies were completed in Caucasians, and the applicability of this evidence to high-risk ethnic populations is unclear.