Acute MI patients with syndrome X more
likely to die in hospital

Of the five hallmarks of metabolic syndrome, hyperglycemia
heightens heart failure risk the most

By Tony Craig

MI AT RISK
A patient is considered to have metabolic syndrome or syndrome X if he or she surpasses the set thresholds in three out of five characteristics: waist circumference; blood pressure; and concentrations of triglycerides, high-density lipoprotein (HDL) cholesterol, and fasting plasma glucose. What does it all mean in terms of cardiac outcomes? Rather a lot, according to French research published in the May 23 edition of the Archives of Internal Medicine. The study looked not at heart attack rates, but at heart failure in hospitalized patients who had already suffered acute myocardial infarction (AMI). "In-hospital case fatality was higher in patients with metabolic syndrome compared with those without, as was the incidence of severe heart failure," claim the authors in their study.

The research team, led by Dr Yves Cottin from the University of Burgundy in Dijon, France followed 633 consecutive patients hospitalized after heart attack, and categorized them according to metabolic criteria. Two hundred and ninety, or 46%, met the National Cholesterol Education Program's (NCEP) Adult Treatment Panel (ATP) III definition of metabolic syndrome. Female sex and advanced age were both risk factors for syndrome X in this group.

REMOVING THE X FACTOR
The metabolic syndrome patients generally had more risk factors for heart failure than the other AMI patients — a fact that complicated the task of analysis. It therefore came as little surprise that their in-hospital fatality rate was more than twice as high, and their heart failure rate nearly twice as high as the AMI patients without the syndrome. But multivariate analysis was able to tease out the particular contribution to risk of each metabolic factor. By far the biggest culprit was hyperglycemia, which was associated with a 3.3-fold increase in heart failure risk.

Oddly, metabolic syndrome had no apparent impact on rates of arrythmias or recurrent AMI. But the syndrome was associated with higher rates of cardiogenic shock, and to vascular damage in the carotid artery and lower leg, suggesting that it could also play a role in stroke and peripheral vascular disease.

AN X-PLANATION?
How metabolic syndrome contributes to cardiovascular disease remains open to speculation. "In patients with diabetes," muse the authors, "several combined mechanisms may contribute to the development of congestive heart failure. Diastolic and/or systolic dysfunction associated with diabetic cardiomyopathy, abnormal myocardial substrate metabolism resulting in increased free fatty acid metabolism, and impaired blood flow to the noninfarcted myocardium are potential factors."

An Italian study led by Dr Roberto Pontremoli from the University of Genoa and published in the May issue of the Journal of Internal Medicine puts forth a different theory. The research was aimed at unearthing why hypertensive patients with metabolic syndrome are at greater risk of cardiovascular disease. The authors suggest that "an association between metabolic syndrome and the presence of target organ damage provides a rationale [for] the increased occurrence of cardiovascular complications." Among the 354 hypertensive subjects enrolled in the study, those with metabolic syndrome were twice as likely to have microalbuminuria, left ventricular hypertrophy or carotid abnormalities. For more on this study, refer to the article "Why metabolic syndrome plus hypertension equals heart trouble" in our last issue.

For the moment, there seems little that can be done for MI patients, except to follow the authors' final injunction: "This study ... confirms the importance of evaluating glycemic control during the acute phase of MI."

Arch Intern Med May 23, 2005;165:1192-8