Metabolic Syndrome Linked to Compromised Heart Structure and Function

PORTO, Portugal, June 7 -- As metabolic syndrome becomes more severe, symptomatic heart failure and several cardiac structural and functional abnormalities may increase progressively, researchers here reported.

This association was independent of the 10-year predicted risk of coronary heart disease by the standard Framingham risk score for indirect indices of diastolic dysfunction, although not systolic function, Ana Azevedo Ph.D., of the University of Porto here, and colleagues reported online in BMC Cardiovascular Disorders.

There was been much debate about the usefulness of the metabolic syndrome in cardiovascular risk prediction, namely whether it adds information to that provided by its individual components, and whether it adds to alternative prediction tools, including the widely used Framingham risk score, Dr. Azevedo wrote.

The current findings came from a cross-sectional study of a random sample of the urban population of Porto, which included 684 participants, ages 45 or older, recruited from 2001 to 2003.

Data were collected by a structured clinical interview with a physician, ECG, and a transthoracic M-mode and 2D echocardiogram.

Metabolic syndrome was defined according to the National Cholesterol Education Program. It included:

• Waist circumference more than 102 cm in men and more than 88 cm in women.
• Fasting serum triglycerides of 150 mg/dL or more.
• High-density lipoprotein (HDL) cholesterol of less than 40 mg/dL in men and less than 50 mg/dL in women.
• High blood pressure: systolic blood pressure of 130 mm Hg or higher and/or diastolic blood pressure of 85 mm Hg or higher, antihypertensive drug treatment;
• High glucose levels: fasting serum glucose pf 110 mg/dL or higher, or clinical diagnosis of diabetes.

The association between the number of features of the metabolic syndrome and the cardiac structural and functional abnormalities was adjusted for age and gender, the 10-year predicted risk of coronary heart disease by the Framingham risk score, and adjusting for age, gender, and systolic blood pressure.

There was a positive association between the number of elements in the metabolic syndrome and features of cardiac structure and function, with a consistent and statistically significant trend for all cardiac variables when adjusting for age and gender.

Measures of left-ventricular geometry patterns, left-atrial diameter, and diastolic dysfunction maintained this trend when taking into account the 10-year predicted risk of coronary heart disease by the Framingham score as an independent variable, while left ventricular systolic dysfunction did not, the researchers said.

Measures of left-ventricular diastolic dysfunction, and mean left- ventricular mass, left-ventricular diameter, and left-atrial diameter increased significantly with increasing numbers of metabolic syndrome features when additionally adjusting for systolic blood pressure as a continuous variable, the researchers reported. Left ventricular systolic dysfunction did not support this trend, they said.

Of all the participants, 19.7% had metabolic syndrome, which was more common among women than men.

High blood pressure was by far the most prevalent single component of the syndrome and affected about 75% of all participants. In this group 80% had hypertension (140/90 mmHg) or used antihypertensive medication.

Men had a higher predicted risk of coronary heart disease, according to the Framingham prediction score.

Cardiac abnormalities were also fairly common in this sample and heart failure (stage C) affected 8.4% of the women and 5.2% of the men.

Concurrence of the various components of the metabolic syndrome increased significantly with age and the syndrome was also significantly and strongly associated with the predicted 10-years risk of coronary heart disease by the Framingham score. Prevalence raged from 6.5 for one metabolic syndrome, for example, to 18.4 for four to five features (P for trend= 0.002).

There was a positive association between the degree of the metabolic syndrome-assessed as the number of concurrently present components-and measures of cardiac structure (left-ventricular diameter and mass, posterior wall height and interventricular septum height) and function.

In a subsample analysis of 541 patients younger than 75 with no coronary heart disease, the adjusted prevalence of left ventricular systolic dysfunction increased with increasing degree of metabolic syndrome, but the association was not statistically significant (P for trend 0.19) when adjusting for the Framingham risk score, the researchers reported.

Importantly, the researchers said, early asymptomatic stages of cardiac dysfunction increased progressively with the severity of the metabolic syndrome, independent of systolic blood pressure.

The statistical association with increasing number of features of metabolic syndrome can be explained by the increasing impact of multiple independent risk factors and does not necessarily mean that there is synergism, the researchers said.

Given the tendency of individual factors to aggregate, the prevalence of each component in isolation was very low, except for high blood pressure. Therefore, it was not possible to estimate the sole effect of each factor, in comparison with the absence of all factors, the researchers said.

From the clinical and public health perspective, it has been questioned whether the metabolic syndrome improves cardiovascular risk prediction, beyond previously used tools such at the diabetes predicting model or the Framingham risk score for coronary heart disease, the researchers said

One must keep in mind, they said, that coronary heart disease is not the only determinant of systolic and diastolic dysfunction. Adjusting for the Framingham risk score amounts to assessing the effect of features of the metabolic syndrome not considered in the Framingham score, such as obesity and triglycerides, among other features, the researchers noted.

If there is increasing insulin resistance with increasing degree of metabolic syndrome, there might be a mitogenic stimulus for cardiac hypertrophy, the researchers wrote. It is not surprising therefore that cardiac structural features were significantly associated with increasing severity of the metabolic syndrome, even when adjusting for the Framingham risk score.

The main limitation of the study, the investigators said, is its relatively small sample size leading to few outcomes in certain categories, such as left ventricular systolic dysfunction, and difficulty assessing interactions within the metabolic syndrome. The cross-sectional design was also not the ideal approach for assessing causality.

Given that increasing concurrence of the metabolic syndrome factors might be only a proxy for higher blood pressure, it is a strength of this study that the reported associations were not explained by blood pressure level, the researchers said.

This association between the metabolic syndrome and compromised structure and function of the heart was independent of the 10-year predicted risk of coronary heat disease by the Framingham risk score for indirect indices of diastolic dysfunction, although not systolic function, the investigators said.

"Metabolic syndrome may help predict and increased cardiovascular risk beyond that predicted by the more frequently use Framingham risk score," Dr. Azevedo wrote.