The predictive value of Tp−Te interval, Tp−Te/QT ratio, and QRS‐T angle of idiopathic ventricular tachycardia in patients with ventricular premature beats

Identify idiopathic ventricular tachycardia in patients with ventricular premature beats was required to have effectively treatment.

Ventricular arrhythmia includes ventricular premature beat, ventricular tachycardia, ventricular flutter, and ventricular fibrillation. The common causes are structural heart disease and ion channel disease.
It is also common in patients without structural heart disease. 1 Idiopathic ventricular premature beat/ventricular tachycardia refers to ventricular arrhythmia without organic heart disease, electrolyte abnormality, and abnormal ion channel function. Most of them originate from left or right ventricular outflow tract. 2,3 Longterm and high-load idiopathic ventricular premature ventricular complex/ventricular tachycardia (PVC/VT) can also lead to tachycardia cardiomyopathy and affect cardiac function. 4 Among them, sustained idiopathic VT can lead to syncope or sudden death in severe cases.
Tp−Te interval refers to the interval from peak of T wave to end of T wave. Tp−Te/QT ratio refers to the ratio of ventricular relative refractory period to total refractory period. 5 QRS-T angle reflects the relationship between ventricular depolarization and repolarization, which can be divided into frontal QRS-T angle (f(QRS-T)angle) and spatial QRS-T angle (s(QRS-T)angle). 6 These indexes are closely related to ventricular repolarization dispersion. It is reported that these indexes are related to the occurrence of ventricular arrhythmia caused by organic heart diseases. 7,8 However, the relationship between these indexes and idiopathic ventricular arrhythmia is seldom reported. The aim of this study is to investigate the predictive value of Tp−Te interval, Tp−Te/QT ratio, and QRS-T angle of idiopathic ventricular premature beats in patients with idiopathic ventricular premature beats.

| Ethical issues
The single-center retrospective study was performed in full accordance with the principles outlined in the Declaration of Helsinki, and permission was obtained from the ethics committee of Soochow University.

| Patients and study design
This study was a retrospective cohort analysis. A total of 178 patients (50.67 ± 17.9 years, 89 male) without any exclusion criteria who had undergone PVC/VT ablation between January 01, 2021 and August 30, 2022. All the selected patients did not use antiarrhythmic drugs or stopped using antiarrhythmic drugs for five half lives before ablation. Ventricular premature beat or ventricular tachycardia that has the same morphology with PVC were recorded by Holter. Exclusion criteria: (1) Patients with severe liver and kidney disease, electrolyte abnormality, thyroid dysfunction, nervous system disease, and diabetic patients with poor blood glucose control; (2) Patients with coronary heart disease, cardiomyopathy, congenital heart disease, valvular heart disease, and other structural heart diseases; (3) Patients with other tachyarrhythmia or bradyarrhythmia, such as atrial fibrillation, sick sinus syndrome, and so forth. At the same time, we selected 75 cases for physical examination in our hospital as the control group and matched with the gender, age, and other factors of the premature ventricular arrhythmia group.     (Figure 1).

| QTc interval, Tp−Te interval, Tp−Te/QT ratio, and QRS-T angle in sustained and nonsustained VT group
Tp−Te interval was significantly longer in sustained VT group than that in nonsustained VT group (105.70 ± 23.01 vs. 93.52 ± 11.25 ms, p = .009). There were no difference between other indexes ( Table 3).
The area under the ROC curves was 0.67 for Tp−Te (Figure 2).   QT interval means the ventricular repolarization but is affected by heart rate. QTc interval is corrected QT interval by heart rate, but it still cannot reflect the real transmural dispersion of ventricular repolarization. Our research showed that QTc interval in the idiopathic ventricular arrhythmia group was longer than that in the control group, but there was no difference between PVC group and PVC with VT group, and between sustained and nonsustained VT group.

| DISCUSSION
Tp−Te interval is the interval from the peak of T wave to the end of T wave. Tp represents the complete repolarization of epicardium, considered as a independent predictor of ventricular arrhythmia in patients with heart disease. 13 The prognostic significance of increased QRS-T angle is most likely to be due to an abnormal axis T A B L E 3 Comparison of QTc, Tp−Te, and Tp−Te/QT ratio between isolated PVC with sustained VT and nonsustained VT. of the T-wave, which reflects an abnormal sequence of ventricular repolarization which may lead to a fatal arrhythmia. 7 But there are few reports about QRS-T angle and idiopathic VT. Our study showed that patients with increased QRS-T angle in idiopathic ventricular arrhythmia group were more than in control group, and were more in PVC with VT group than in PVC group, but there was no significant difference between sustained and nonsustained VT group.
In clinical practice, we found that some patients with ventricular premature beats will not affect the cardiac structure and function in a short time. However, some patients with idiopathic ventricular tachycardia have syncope, hypotension and even sudden cardiac death when tachycardia attacks. A few of them have ventricular tachycardia as their initial and only manifestation. Implantable cardioverter defibrillator or radio frequency ablation should be carried out for these patients. The need of careful follow-up and using noninvasive tool to identify high-risk patients was required to have effectively treatment.

| CONCLUSION
Tp−Te interval, Tp−Te/QT ratio, and QRS-T angle may has a predictive value of presence of idiopathic VT and the combined prediction of these indexes is more valuable. Tp−Te interval maybe helpful for prediction of sustained idiopathic VT.