The reason why obese patients often fare better after they undergo coronary by-pass surgery than other patients so may simply be because they are referred for treatment at an earlier stage of their disease, new research suggests.

Why obesity, which raises the risk of all causes of death, is associated with better short-term outcomes after heart by-pass surgery - the so-called “obesity paradox” - has been unclear, Dr. Ronen Rubinshtein, from Lady Davis Carmel Medical Center in Haifa, Israel, and colleagues note in the American Journal of Cardiology.

To solve this mystery, the researchers examined the association between body mass index (weight to height ratio commonly used to determine obesity) along with severity of heart disease and blockage locations that confer a higher risk, in 928 consecutive patients who underwent coronary imaging (angiography) over a 6-month period.

Obese patients were younger and more likely to have High cholesterol, high blood pressure and diabetes than were patients who were not obese, the report indicates. Obese patients also had lower rates of high-risk location and severity of heart disease, defined as at least 50 percent blockage of the left main coronary artery or significant disease in three coronary arteries.

Analysis confirmed that obese patients had a lower risk of having high-risk coronary blockages, whereas advancing age, male gender, diabetes, and High cholesterol were all linked to a greater risk of difficult coronary anatomy.

No significant difference in mortality at 30 to 36 months was noted based on body mass index, whereas the presence of high-risk coronary arteries was associated with a greater mortality risk, the researchers point out.

These findings may result from physicians referring their obese patients for coronary imaging sooner than they would patients with normal weights, the authors conclude.

SOURCE: American Journal of Cardiology, May 1, 2006.