QT Dispersion and Drug-Induced Torsade de Pointes

Is There Any Correlation Between QT Dispersion and Echocardiographic Indices in Term Neonates with and Without Maternal Gestational Diabetes Mellitus?

Background: Gestational diabetes mellitus (GDM) can cause diastolic dysfunction and asymmetric ventricular septal hypertrophy in infants of gestational diabetic mothers (IGDMs). Ventricular thickness can affect QT interval and other QT parameters. Objectives: This study aimed to evaluate and compare the duration of QT, corrected QT (QTc), QT dispersion (QTD), and echocardiographic indices in two groups of neonates of mothers with and without GDM. Methods: In this case-control study, 76 term neonates were enrolled. The case group (n = 38) included IGDM, and the control group (n = 38) included neonates born to healthy mothers. The QT, QTD, and QTc were calculated based on electrocardiographic results. Ejection fraction (EF), interventricular septal thickness at the end of diastole (IVSTD), left ventricular end-diastolic diameter (LVEDD), left ventricular end-systolic diameter (LVESD), and left ventricular posterior wall thickness (LVPWT) were evaluated by performing echocardiography, and the two groups were compared regarding them. Data were analyzed using SPSS version 21. Results: In this study, neonates' mean age and weight were 4.18 ± 1.3 days and 3418.16 ± 549.24 grams, respectively. As for the gender of neonates, 68.4% in the case group and 47.4% in the control group were female. The two groups had no significant difference regarding age, weight, and sex (P > 0.05). Minimum QTc (QTc min) was significantly higher in the case group (P = 0.046). Considerably lower EF and higher IVSTD were found in the case group (P = 0.011 and P = 0.05 respectively). In univariate analysis, echocardiographic parameters were not the predictors of QTD (P > 0.05); in multivariate analysis, however, QTD was significantly correlated with LVEDD (P = 0.001) and LVESD (P = 0.015). Conclusions: A higher proportion of septal hypertrophy was detected in IGDMs compared to infants of the healthy mothers without any correlation with ECG indices. This involvement was accompanied by relatively decreased EF verified by echocardiography. Most ECG findings, including QTD values, had no linear relationship with echocardiographic parameters except for LVEDD and LVESD.

Vicious LQT induced by a combination of factors different from hERG inhibition

Clinically, drug-induced torsades de pointes (TdP) are rare events, whereas the reduction of the human ether-à-go-go-related gene (hERG) current is common. In this study, we aimed to explore the specific factors that contribute to the deterioration of hERG inhibition into malignant ventricular arrhythmias. Cisapride, a drug removed from the market because it caused long QT (LQT) syndrome and torsade de pointes (TdP), was used to induce hERG inhibition. The effects of cisapride on the hERG current were evaluated using a whole-cell patch clamp. Based on the dose-response curve of cisapride, models of its effects at different doses (10, 100, and 1,000 nM) on guinea pig heart in vitro were established. The effects of cisapride on electrocardiogram (ECG) signals and QT interval changes in the guinea pigs were then comprehensively evaluated by multi-channel electrical mapping and high-resolution fluorescence mapping, and changes in the action potential were simultaneously detected. Cisapride dose-dependently inhibited the hERG current with a half inhibitory concentration (IC50) of 32.63 ± 3.71 nM. The complete hERG suppression by a high dose of cisapride (1,000 nM) prolonged the action potential duration (APD), but not early after depolarizations (EADs) and TdP occurred. With 1 μM cisapride and lower Mg2+/K+, the APD exhibited triangulation, dispersion, and instability. VT was induced in two of 12 guinea pig hearts. Furthermore, the combined administration of isoproterenol was not therapeutic and increased susceptibility to ventricular fibrillation (VF) development. hERG inhibition alone led to QT and ERP prolongation and exerted an anti-arrhythmic effect. However, after the combination with low concentrations of magnesium and potassium, the prolonged action potential became unstable, triangular, and dispersed, and VT was easy to induce. The combination of catecholamines shortened the APD, but triangulation and dispersion still existed. At this time, VF was easily induced and sustained.