Insulin Resistance Tied to Early Heart Problems

According to Gautam Singh, MD, of Washington University in St. Louis, teens who had elevated fasting plasma insulin and insulin resistance were significantly more likely to have multiple measures of cardiac dysfunction than those with normal values.

And in a multivariate analysis, increased fasting plasma insulin and insulin resistance, along with rising body mass index (BMI), were associated with poorer left ventricular function (P<0.05 for all).

Singh noted that, the cardiac changes represent the early onset of impaired left ventricular function even before the clinical manifestations of any cardiac dysfunction are there.

Although some of these changes have been demonstrated in a pediatric population before, they have not been linked previously to insulin resistance, he said.

The next step in the research is to follow these patients longitudinally to see whether the cardiac changes continue, and whether they can be reversed by improving lifestyle and losing weight. Just knowing that the heart is being affected at such a young age can provide the impetus for a child or parent to make the necessary lifestyle adjustments.

Because obesity tends to track from childhood to adulthood, Singh and his colleagues wanted to see whether obesity-related cardiac dysfunction also would track. They hypothesized that it would and that insulin resistance would be an important mediator in the process.

The researchers prospectively enrolled 77 teens (mean age 13.9) who went to a preventive cardiology clinic or gastroenterology clinic for the evaluation of dyslipidemia, obesity, and hypertension. Singh and his colleagues measured glucose-insulin homeostasis, metabolic profiles, and left ventricle global longitudinal strain, as well as strain rate and torsion using 2D speckle-tracking echocardiography.

The participants were divided into two groups, normal: teens with normal fasting plasma insulin of 10 µIU/mL or lower and normal insulin resistance indicated by a HOMA2 of 2 or lower and abnormal: teens with higher values.

The average BMI was significantly higher in the abnormal group (33.9 versus 26 kg/m2). This group also had a significantly higher systolic and diastolic blood pressure (P<0.05 for both).

Although fasting insulin, fasting glucose, and insulin resistance were higher in the abnormal group, the lipid profile was similar in each group. There were also no between-group differences in liver enzymes or thyroid hormones.

Echocardiography showed that left ventricular mass and ejection fraction were not significantly different between the two groups. However, left ventricular global longitudinal strain, longitudinal systolic strain rate, and early diastolic strain rate were all significantly decreased in the abnormal group (P<0.04 for all), indicating early left ventricular dysfunction. Insulin resistance was inversely associated with all three measures.

Singh stated that, the mechanism underlying the decrease in myocardial longitudinal strain and circumferential torsion is not clear and presumes that insulin resistance is causing cardiac dysfunction by modifying myocardial substrate metabolism and efficiency, which has been suggested in both animal and human studies.

Singh G, et al "Insulin resistance is a determinant of cardiac dysfunction in obese children" ASE 2011; Abstract P1-72