QT_c Duration is Associated With Levels of Insulin and Glucose Tolerance: The Zutphen Elderly Study

Prolongation of heart rate-adjusted QT length (corrected QT interval [QT_c]) is associated with elevated risk of coronary heart disease and sudden death. This may have to do with autonomic cardiac control. Because insulin is known to stimulate sympathetic activity, we studied the association of insulin level and glucose tolerance with QT_c. In 1990, 383 elderly men 70–89 years of age without previous myocardial infarctions or known diabetes had a 12-lead electrocardiogram recorded and glucose tolerance determined in the frame of an ongoing follow-up study. QT_c was significantly associated with fasting glucose, insulin, and C-peptide and glucose levels 60 and 120 min after an oral glucose load. For fasting C-peptide and the area under the glucose curve (AUGC), this association could not be explained by the concomitant occurrence of other risk factors of coronary heart disease. Furthermore, fasting C-peptide and the AUGC were independently additive predictors of QT_c duration. The difference in QT_c between men in the extreme quintiles of both variables was 22 ms. QT_c prolongation seems to be part of the insulin resistance syndrome. The association may be explained by increased sympathetic activity induced by high insulin levels. An additional explanation could be an effect of high insulin, impaired glucose utilization, or both on membrane activity of myocardial cells.