The Relationship Between QT Dispersion and Serum Insulin, Glucose Levels

QT dispersion (QTD) and rate-corrected QTD (QTcD) reflect inhomogeneity of repolarization of the ventricular myocardium. This study was performed to evaluate the relationship between blood insulin c-peptide, glucose levels and QTD,QTcD. In twenty-two healthy volunteers ( 17 male, 5 female; mean age 48.7±10.1 year) QTD, blood glucose, c-peptide levels were measured O, 30, 60, 90 and 120 minutes after 75 g oral glucose load. QTcD was calculated with the Bazett's formula. Mean values for QTD were 15.6±5.1, 30.4±9.5, 35.8±11.8, 24.6±9.5, 20.6±7.3 ms and for QTcD were 17.3±5.l, 34.6±11.2, 40.4±13.5, 30.1±11.0, 22.7±8.0 ms. Blood glucose averaged 81.8±16.1, 125.1 ±33.8, 160.3±38.8, 158.1±64.8, 122.5±54.5 mg/dL; and c-peptide 2.2±0.6, 6.3±1.9, 9.7±1.6, 9.3±2.7, 8.1±3.3 ng/dL, respectively. There was a positive correlation between c peptide level and QTD (r=0.412, p<0.01), QTcD (r=0.431,p<0.005) and between glucose level and QTD (r=0.512, p<0.001), QTcD (r=535, p<0.001). QTD and QTcD at the 60th min after glucose load were at the highest level. There was a parallel shortening of the QTD, QTcD with the c-peptide, glucose decrease. This study indicated that QTD and QTcD get longer with hyperglycemia and hyperinsulinemia and probably this effect is due to the modulation of cardiac cell membrane potential by insulin.