Acute effects of electronic cigarette smoking on ventricular repolarization in adults

Background: Electronic cigarette (e-cigarette) use is constantly increasing. However, the association between e-cigarette use and ventricular arrhythmia is unknown. Thus, in this study, we aimed to evaluate the markers of ventricular repolarization such as QT interval, corrected QT (QTc), QT dispersion (QTd), peak-to-end interval of the T wave (Tp-e), corrected Tp-e and Tp-e/QT ratios in e-cigarette users. Methods: The study population consisted 36 e-cigarette users and 40 healthy subjects. Ventricular repolarization parameters were obtained from 12-lead resting electrocardiogram. Ventricular repolarization parameters of the groups were compared. Results: Basal demographic and laboratory data were similar in both groups. According to the electrocardiographic parameters, the Tp-e interval, corrected Tp-e, and Tp-e/QT ratio were significantly higher in individuals using e-ciga- rettes than in control subjects [74.9±6.4 milliseconds (ms) vs. 80.1±4.1ms, <0.001; 82.9±7.5 ms vs. 87.8±6.3 ms, p=0.003; 0.20±0.01 vs. 0.21±0.01, p=0.002; respectively]. Conclusion: This is the first study to show the disruption of ventricular repolarization properties in e-cigarette users. E-cig- arette use in terms of public health leads to augmentation of transmural dispersion of repolarization, which may be potential indicator of ventricular arrhythmogenesis. Keywords: Electronic cigarette; ventricular repolarization; Tp-e interval; Tp-e/QT ratio.

Assessment of Transmural Dispersion of Repolarization in Children with Mitral Valve Prolapse

Background: Children with mitral valve prolapse (MVP) may be prone to ventricular arrhythmias due to transmural dispersion of repolarization (TDR). This study aimed to assess alterations in ventricular repolarization in children with MVP and to investigate their relationships with the degree of mitral regurgitation. Methods: Fifty children with MVP and 50 age- and sex-matched healthy children as controls were studied. Twelve-lead electrocardiography and echocardiography were performed in all the subjects. TDR parameters were QT and QTc intervals, QTc dispersion, Tp-e interval, Tp-e interval dispersion, Tp-e/QT, Tp-e/QTc, JTc, JTc dispersion, Tp-e/JT, and Tp-e/JTc. Results: The mean age of the 50 patients with MVP was 12.45±2.50 years (F/M: 15/35). There were no significant differences in QT and QTc intervals between the 2 groups. QTc dispersion (P=0.001), Tp-e dispersion interval (P=0.002), Tp-e/QTc (P=0.001), JTc dispersion (P=0.023), Tp-e/JT (P=0.004), and Tp-e/JTc (P=0.002) were significantly higher in the patients with MVP than in the healthy controls. Positive correlations were found between Tp-e dispersion interval and Tp-e/QTc and an increase in the degree of mitral regurgitation (P=0.012, r=0.42 and P=0.004, r=0.31, respectively). Additionally, positive correlations were detected between JTc dispersion and Tp-e/JTc and an increase in the degree of mitral regurgitation (P=0.032, r=0.20 and P=0.024, r=0.42, correspondingly). Conclusion: In this study, TDR was damaged in children with MVP and was positively correlated with an increase in the degree of mitral regurgitation. It appears that children with MVP are prone to life-threatening ventricular arrhythmias.

Different effects of amiodarone and dofetilide on the dispersion of repolarization between well-coupled ventricular and Purkinje fibers1

Increased transmural dispersion of repolarization is an established contributing factor to ventricular tachyarrhythmias. In this study, we evaluated the effect of chronic amiodarone treatment and acute administration of dofetilide in canine cardiac preparations containing electrotonically coupled Purkinje fibers (PFs) and ventricular muscle (VM) and compared the effects to those in uncoupled PF and VM preparations using the conventional microelectrode technique. Dispersion between PFs and VM was inferred from the difference in the respective action potential durations (APDs). In coupled preparations, amiodarone decreased the difference in APDs between PFs and VM, thus decreasing dispersion. In the same preparations, dofetilide increased the dispersion by causing a more pronounced prolongation in PFs. This prolongation was even more emphasized in uncoupled PF preparations, while the effect in VM was the same. In uncoupled preparations, amiodarone elicited no change on the difference in APDs. In conclusion, amiodarone decreased the dispersion between PFs and VM, while dofetilide increased it. The measured difference in APD between cardiac regions may be the affected by electrotonic coupling; thus, studying PFs and VM separately may lead to an over- or underestimation of dispersion.