Cardiac Repolarization in Health and Disease

Novel risk predictor of arrhythmias for patients with potassium channel-related congenital long QT syndrome

BACKGROUND

Congenital long QT syndrome (LQTS) is characterized by delayed ventricular repolarization, predisposing to potentially lethal ventricular arrhythmias. The variability in disease severity among patients remains largely unexplored, underscoring the limitations of current risk stratification methods.

OBJECTIVE

We aimed to evaluate the potential utility of electrocardiographic markers from the exercise stress test (EST) in identifying patients with high-risk LQTS.

METHODS

The study, which considered patients with LQTS type 1 and LQTS type 2, comprised a discovery cohort of 695 and a validation cohort of 635 patients.

RESULTS

The change in corrected QT (QTc) interval between rest and recovery (between rest and 3-4 minutes into the recovery period, called recovery-rest ΔQTc) was consistently greater in symptomatic patients. Sensitivity analyses performed on EST data obtained on and off β-blockers as well as upon distinguishing between patients with a baseline QTc interval below and those above 470 ms demonstrated consistent findings. The association of recovery-rest ΔQTc with cardiac events remained significant in a subanalysis focusing on future events (ie, occurring after the EST). An optimal recovery-rest ΔQTc cutoff was determined for LQTS type 1 (35 ms) and LQTS type 2 (16 ms) separately and was shown to be significantly associated with cardiac events.

CONCLUSION

Our findings suggest that in patients with LQTS, dynamic QT interval measures obtained during the EST are associated with lifetime arrhythmic events and events after the EST. Such measures can be helpful in identifying a higher-risk subset of patients with LQTS in order to optimize their management. Further research may confirm these findings in larger cohorts and explore the potential benefit of combining genetic and EST data for more precise risk stratification.

KCNQ1 Polymorphism in the Context of Ischemic Cardiomyopathy: A Potential Key to Decision-Making for Device Implantation

BACKGROUND

Ventricular tachyarrhythmia (VTA) in ischemic cardiomyopathy (ICM) is a life-threatening condition influenced by genetic factors and electrical remodeling. This study investigated the association between KCNQ1 gene polymorphisms (rs2237892 and rs2237895) and the development of VTA in ICM patients to improve risk stratification and guide device implantation decisions.

METHODS

This single-center study included 213 ICM patients with implantable cardioverter-defibrillators (ICD) for primary prevention of VTA. Patients were divided into arrhythmia and control groups based on device interrogation findings. Genetic analysis for rs2237892 and rs2237895 polymorphisms was performed using real-time polymerase chain reaction (PCR). Clinical, electrocardiographic, and laboratory parameters were analyzed. Correlation and logistic regression analyses evaluated the association between KCNQ1 polymorphisms and VTA risk.

RESULTS

The arrhythmia group demonstrated significantly higher QT dispersion, frontal QRS-T angle, and T-wave peak-to-end interval compared to the control group. The TT genotype of rs2237892 and the AC genotype of rs2237895 were significantly associated with increased VTA risk (p < 0.001). Multivariate analysis confirmed these genotypes as independent predictors of VTA. No significant differences in other clinical or laboratory risk factors were observed.

CONCLUSIONS

KCNQ1 gene polymorphisms (rs2237892 and rs2237895) are strongly associated with VTA in ICM patients, suggesting a potential role as biomarkers for risk stratification. These findings may assist in tailoring ICD implantation decisions and improving patient outcomes.

Clinical, Electrical, and Mechanical Parameters in Potassium Channel-Mediated Congenital Long QT Syndrome

Background: Congenital long QT syndrome (LQTS) is a rare cardiac disorder caused by repolarization abnormalities in the myocardium that predisposes to ventricular arrhythmias and sudden cardiac death. Potassium channel-mediated LQT1 and LQT2 are the most common types of channelopathy. Recently, LQTS has been acknowledged as an electromechanical disease. Methods: A total of 87 genotyped LQT1/LQT2 patients underwent cardiac evaluation. A comparison between LQT1 and LQT2 electrical and mechanical parameters was performed. Results: LQT2 patients had worse electrical parameters at rest: a longer QTc interval (p = 0.007), a longer Tpe in lead V2 (p = 0.028) and in lead V5 (p < 0.001), and a higher Tpe/QT ratio in lead V2 (p = 0.011) and in lead V5 (p = 0.005). Tpe and Tpe/QT remained significantly higher in the LQT2 group after brisk standing. Tpe was longer in LQT2 patients compared with LQT1 patients during peak exercise (p = 0.007) and almost all recovery periods in lead V2 during EST. The mid-cavity myocardium mean radial contraction duration (CD) was longer in LQT2 patients (p = 0.02). LQT2 patients had a longer mean radial CD in mid-septal (p = 0.015), mid-inferior (p = 0.034), and mid-posterior (p = 0.044) segments. Conclusions: Potassium channel-mediated LQTS has different effects on cardiac electromechanics with a more pronounced impact on LQT2 patients. Tpe was more prominent in the LQT2 cohort, not only at rest and brisk standing but also during EST exercise and at recovery phases. The altered mean radial CD in the mid-cavity myocardium was also specific for LQT2 patients.

[Cardiac channelopathies in the context of hereditary arrhythmia syndromes]

Genetic arrhythmia disorders are rare diseases; however, they are a common cause of sudden cardiac death in children, adolescents, and young adults. In principle, a distinction can be made between channelopathies and cardiomyopathies in the context of genetic diseases. This paper focuses on the channelopathies long and short QT syndrome, Brugada syndrome, and catecholaminergic polymorphic ventricular tachycardia (CPVT). Early diagnosis of these diseases is essential, as drug therapy, behavioral measures, and if necessary, implantation of a cardioverter defibrillator can significantly improve the prognosis and quality of life of patients. This paper highlights the pathophysiological and genetic basis of these channelopathies, describes their clinical manifestations, and comments on the principles of diagnosis, risk stratification and therapy.