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Assessment of QT and JT Intervals in Patients With Left Bundle Branch Block
Peyman Tabatabaei1, Ala Keikhavani2, Majid Haghjoo1
1Cardiac Electrophysiology Research Center, Rajaie Cardiovascular Medical and Research Center, Iran University of Medical Sciences, Tehran, IR Iran.
Insights
The corrected JT interval (JTc) remains stable during right ventricular pacing, unlike the corrected QT interval (QTc). This indicates JTc is a reliable measure of ventricular repolarization, independent of depolarization, for predicting QTc in Left Bundle Branch Block (LBBB) patients.
Area of Science:
- Cardiology
- Electrophysiology
- Cardiac Repolarization
Background:
- Prolonged QT interval is a risk factor for cardiac events.
- Left bundle branch block (LBBB) prolongs the QT interval.
- Corrected QT interval (QTc) may overestimate repolarization changes in LBBB due to depolarization effects.
Purpose of the Study:
- To evaluate the corrected JT interval (JTc) as a measure of ventricular repolarization.
- To determine if JTc can be used to predict QTc in patients with LBBB.
- To assess the impact of right ventricular pacing on JTc and QTc.
Main Methods:
- 101 patients with sinus rhythm and narrow QRS underwent electrophysiology studies.
- Right ventricular apex pacing was used to induce LBBB at different cycle lengths (600 and 700 ms).
- QTc and JTc were measured; JTc was calculated as QTc minus QRS duration.
Main Results:
- Right ventricular pacing significantly increased QTc (P < 0.0001).
- JTc showed no significant change with pacing (P = 0.24).
- JTc was independent of QRS duration, while QTc correlated with QRS duration.
Conclusions:
- Right ventricular pacing prolongs QTc but not JTc.
- JTc accurately reflects ventricular repolarization, independent of depolarization.
- JTc is a suitable index for predicting QTc in patients with LBBB.
Background:
Prolongation of the QT interval is considered a risk factor for cardiac adverse events and mortality. Left bundle branch block (LBBB) lengthens the QT interval. The corrected QT interval (QTc) is most likely overestimated because its prolongation is caused by increases in depolarization duration and not in repolarization.
Objectives:
In this study, we aimed to apply corrected JT interval (JTc) as an appropriate measure of ventricular repolarization for predicting QTc in a formula.
Patients And Methods:
The study population consisted of 101 patients with sinus rhythm (SR) and narrow QRS complexes (< 120 milliseconds). All patients underwent electrophysiology studies or ablation. A diagnostic catheter was positioned in the right ventricular apex (RVA) to induce LBBB at two different cycle lengths (CLs; 600 and 700 mv). The intrinsic QRS complex, QT time, and JT time were measured during SR and subsequent RVA pacing. The JTc was derived simply by subtracting the QRS duration from the QTc.
Results:
Stimulation from the RVA increased the QTc from 456.20 ± 38.63 ms to 530.67 ± 47.73 ms at a CL of 600 (P < 0.0001) and to 502.32 ± 47.26 ms at 700 CL (P < 0.0001). JTc showed no significant changes with stimulation from the RVA (102.97 ± 11.35 ms vs. 103.59 ± 10.67 ms, P = 0.24). There was no significant correlation between JTc and QRS complex duration. A significant correlation was seen between QRS and QTc at both CLs. The ROC curve indicated that sensitivity of 80% and specificity of 67% were obtained with JTc duration of 92.6 ms.
Conclusions:
Right ventricular pacing increases the QT interval without increasing the JT interval. Our results confirm that JTc, as an index of repolarization, is independent of ventricular depolarization. Therefore, it can be applied for predicting QTc in patients with LBBB.
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