The JT interval as a depolarization independent measurement of repolarization: lessons from catheter ablation of the Wolff-Parkinson-White syndrome

Assessment of QT and JT Intervals in Patients With Left Bundle Branch Block

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.

Risk of Mortality Associated With QT and JT Intervals at Different Levels of QRS Duration (from the Third National Health and Nutrition Examination Survey)

QT prolongation in the setting of QRS >120 ms is believed to be triggered by prolonged depolarization rather than repolarization. Hence, JT interval is suggested as an alternative to QT interval when QRS duration is prolonged. It is unclear, however, if JT and QT intervals portend similar risk of mortality for different durations of QRS. We examined the association between QT and JT, separately, with all-cause mortality across different levels of QRS duration in 8,025 participants (60 ± 13 years, 41% white and 54% women) from the Third National Health and Nutrition Examination Survey. At baseline (1986 to 1994), 486 participants (6%) had QRS duration ≥120 ms. During a follow-up of up to 18 years, 3,045 deaths (38%) occurred. There were significant nonlinear relations of QT and JT intervals with mortality (p <0.001). Hence, QT and JT were categorized as prolonged (>95th percentile), shortened (<5th percentile), and normal (reference group). In multivariate-adjusted Cox regression models, prolonged JT (hazard ratio [HR] 4.75, 95% confidence interval [CI] 1.86 to 12.11) was associated with increased risk of mortality more than prolonged QT (HR 1.50, 95% CI 1.03 to 2.17) in participants with QRS ≥120 ms (interaction p = 0.02). In participants with QRS duration <120 ms, prolonged QT and JT were equally predictive of all-cause mortality (HR 1.27, 95% CI 1.06 to 1.54, and HR 1.31, 95% CI 1.10 to 1.55, respectively). Similar patterns were observed with shortened QT and JT intervals. In conclusion, although both QT and JT intervals are predictive of mortality, JT is more predictive in the setting of QRS duration >120 ms supporting the use of JT interval in patients with prolonged QRS.

Alterations of Blood Pressure and ECG following Two-Week Consumption of Berberis integerrima Fruit Extract

In light of the popularity and also the various nutritional and medicinal properties of Berberis integerrima, this study was conducted to assess the influence of its aqueous extract on hemodynamic and electrocardiogram (ECG) indices of rat. Animals were divided to control (CTL), B50, B100, and B200 groups that orally received tap water, aqueous extracts of B. integerrima fruit 50, 100, and 200 mg/kg/day, respectively, for two weeks and on day 15, data were recorded. Different doses of barberry fruit extract had no significant effect on blood pressure, heart rate, RR interval, P duration, and Q wave amplitude of electrocardiogram. Extract administration was associated with an incremental trend in PR interval that was not statistically significant. Higher doses (100 and 200 mg/kg) of extract significantly increased the QRS interval (P < 0.01 versus CTL and B50 groups) but decreased the QTc interval (P < 0.01 versus CTL group and P < 0.001 versus B50 group), the JT interval, and TpTe interval (P < 0.001 versus CTL and B50 groups). The results suggest that high doses of barberry extract definitely prolong the depolarization phase and shorten the repolarization phase of ventricular muscle and hence induce alteration in heart electrical conductivity.

Optimal QT/JT interval assessment in patients with complete bundle branch block

BACKGROUND

Prolonged ventricular repolarization duration confers increased risk for malignant ventricular arrhythmias. We sought to clarify the optimal method of QT/JT interval assessment in patients with complete bundle branch block (BBB).

METHODS

Study patients (n = 71) were dual-chamber device recipients with baseline left or right BBB who preserved intrinsic ventricular activation during incremental atrial pacing. Patients were classified according to the presence or not of structural heart disease. The former group received chronic amiodarone therapy. QT and JT intervals were recorded at baseline heart rate of 51 ± 4 beats/min and during atrial pacing at 60, 80, and 100 beats/min. We used linear mixed-effects models to assess the effect of heart rate on the derived QTc and JTc values with the use of six different heart rate correction formulae.

RESULTS

Heart rate had a significant effect on the QTc and the JTc intervals regardless of the correction formula used (P < 0.001 for all formulae). The formula of Hodges demonstrated the least variability in QTc and JTc measurements across the different heart rates in both patients groups without (F = 15.05 and F = 13.53, respectively) and with structural heart disease (F = 5.71 and F = 7.69, respectively), followed by the Nomogram and Framingham methods, whereas the uncorrected QT and JT intervals showed comparable heart rate-dependency. The application of Bazett's JTc and QTc led to the most pronounced interval variations in any case with BBB.

CONCLUSIONS

The Hodges, Nomogram and Framingham correction methods provide best assessment of QT/JT intervals in BBB, whereas Bazett's formula exaggerates heart rate-dependency of ventricular repolarization intervals.

Catheter ablation of a posteroseptal accessory pathway in a case with congenital long QT syndrome

A 23-year-old woman with pre-excitation who was resuscitated from ventricular fibrillation underwent electrophysiologic testing. Successful catheter ablation of a left posteroseptal accessory pathway was achieved. Though the JT and JTc intervals as well as QT and QTc intervals were prolonged before and one day after the ablation, they normalized within about 5 hours after the ablation. This case demonstrated that in a patient with pre-excitation and long QT syndrome (LQTs), the JTc interval was useful for diagnosing LQTs and a longer follow-up of the JTc interval after the ablation was necessary in order not to miss the diagnosis of LQTs.

Effects of Cardiac Resynchronization Therapy on Ventricular Repolarization in Patients with Congestive Heart Failure

INTRODUCTION

Biventricular pacing has been shown to improve the clinical status of patients with congestive heart failure, but little is known about its influence on ventricular repolarization. The aim of our study was to evaluate the effect of biventricular pacing on ECG markers of ventricular repolarization in patients with congestive heart failure.

METHODS AND RESULTS

Twenty-five patients with congestive heart failure, sinus rhythm (SR), and complete LBBB (6 females; age 61 +/- 8 years; NYHA class II-III; echocardiographic ejection fraction 21 +/- 5%; QRS > or = 130 ms) underwent permanent biventricular DDDR pacemaker implantation. A high-resolution 65-lead body-surface ECG recording was performed at baseline and during right-, left-, and biventricular pacing, and the total 65-lead root mean square curve of the QRST complex and the interlead QT dispersion were assessed. The QRS duration was increased during right (RV)- and left ventricular (LV) pacing (127 +/- 26% and 117 +/- 40%; P < 0.05), as compared to SR (100%) and biventricular pacing (93 +/- 16%; ns). The QTc interval was increased during RV and LV pacing (112 +/- 12% and 114 +/- 14%; P < 0.05) as compared to SR (100%) or biventricular pacing (99 +/- 12%). There was no effect on JT interval during all pacing modes. The T(peak-end) interval was increased during right (120 +/- 34%; P < 0.01) and LV pacing (113 +/- 29%; P < 0.05) but decreased during biventricular pacing (81 +/- 19%; P < 0.01). A similar effect was found for the T(peak-end) integral and the T(peak) amplitude. QT dispersion was increased during right ventricular (129 +/- 16 ms; P < 0.05) and decreased during biventricular pacing (90 +/- 12 ms; P < 0.01), as compared to SR (114 +/- 22 ms).

CONCLUSIONS

Using a high-resolution surface ECG, biventricular pacing resulted in a significant reduction of ECG markers of ventricular dispersion of repolarization.

Prognostic significance of corrected QT and corrected JT interval for incident coronary heart disease in a general population sample stratified by presence or absence of wide QRS complex: the ARIC Study with 13 years of follow-up

BACKGROUND

Heart rate-corrected QT interval (QTc) is the traditional method of assessing the duration of repolarization. Prolonged heart rate-corrected QT interval is associated with higher risk of mortality in patients with coronary heart disease (CHD) and in the general population. However, the QTc is typically not evaluated when QRS duration is > or =120 ms, because increased QRS duration (QRSd) contributes to QT interval prolongation. In these circumstances, the JT interval has been proposed as a more valid way to assess ventricular repolarization.

METHODS AND RESULTS

To allow for variation in heart rate, corrected JT interval (JTc) was defined as QTc-QRSd. Using data from the Atherosclerosis Risk in Communities Study, JTc and QTc were compared for their prognostic associations with incident CHD events among 14 696 men and women who were CHD-free at baseline, having either normal conduction or wide QRS complex. Among individuals with normal QRS duration, logistic regression adjusted for age, hypertensive status, diabetes, race, systolic blood pressure, smoking, HDL and LDL cholesterol, R-R interval, and menopausal status in women showed QTc and JTc were nonpredictive of future coronary events in men but significant in women. In individuals with wide QRS complex (QRSd > or =120 ms), similar analyses showed JTc had a significant prognostic advantage compared with QTc in men but not in women, among whom only 11 events occurred.

CONCLUSIONS

The JTc is a simple measurement that is a significant independent predictor of incident CHD events in men with wide QRS complex.

Electrocardiographic repolarization abnormalities in familial dysautonomia: an indicator of cardiac autonomic dysfunction

OBJECTIVE

Electrocardiographic repolarization intervals were evaluated to determine the extent of cardiac autonomic dysfunction in patients with familial dysautonomia (FD) and to determine if any of these intervals could serve as a possible predictor of clinical symptoms.

METHODS

Thirty-seven electrocardiograms of patients with FD were retrospectively evaluated. QT, JT, rate-corrected QT and JT intervals were calculated as well as QT and QTC dispersion. Results were compared to normative data and electrocardiograms of 20 age-matched control subjects.

OBSERVATIONS

In the FD group, prolongation of QTC (>450 msec) was noted in 5/37 (13.5%) patients, as compared to 0/20 normal controls (p = NS), and prolongation of JTc (>340 msec) in 16/37 (43.3%) patients, as compared to 0/20 normal controls (p < 0.001). QT and QTC dispersion were abnormal in 3/37 (8.1%) and 5/37 (13.5%), respectively. In the 16 FD patients with prolonged JTc, six had a positive history of syncope, whereas none of the 21 with normal JTc had syncope or symptoms suggesting arrhythmia (p < 0.003). The positive predictive value of having syncope or symptoms suggestive of arrhythmia with an abnormal JTc is 37.5% (95% CI [15%, 65%]). The negative predictive value is 100% (95% CI [87%, 100%]).

CONCLUSION

In the FD population, the electrocardiographic measure of repolarization that was most frequently abnormal was the JTc interval . Prolongation of the JTc interval was significantly more frequent than prolongation of the QTC interval (p < 0.001) QT and QTC dispersions were less significantly affected in the FD population, indicating uniform ventricular recovery time. These results suggest that a prolonged JTc interval may be a more sensitive indicator of abnormal ventricular repolarization and cardiac autonomic dysfunction. Due to the known sympathetic denervation inherent in patients with FD, they are at risk for unopposed parasympathetic predominance. FD patients, therefore, are more likely to have brady arrhythmias and asystole rather than polymorphic ventricular tachycardia. The increased incidence of syncope in patients with prolonged JTc suggests that this measure may serve as a helpful marker to predict which FD patients are at increased risk of serious clinical sequelae including bradyarrhythmias with asystole or sudden death.

JT dispersion in Wolff-Parkinson-White syndrome: effect of eccentric ventricular depolarization on the dispersion of repolarization

There is much interest in QT dispersion for noninvasive risk stratification of patients at risk of arrhythmias. However, little is known about the genesis of abnormal QT dispersion. In particular, whether eccentric ventricular depolarization, as seen in preexcitation, can lead to abnormal dispersion of repolarization is unknown. We studied 24 children aged 1-19 years (mean +/- SD, 11 +/- 5 years) with manifest preexcitation due to Wolff-Parkinson-White syndrome who had successful catheter ablation. Standard ECGs done preablation, early postablation (< 1 week), mid postablation (> 1 week, < 2 months), and late postablation (> 2 months) were reviewed. The QRS duration prior to ablation ranged from 90-160 ms (mean +/- SD, 123 +/- 21 ms). On the preablation ECG, the JT and JTc dispersions showed no relationship to the QRS duration (r = 0.04 and 0.07, respectively). There was no change in JT dispersion when the preablation (42 +/- 15 ms) ECG was compared to early (43 +/- 15 ms), mid (44 +/- 13 ms), and late postablation (48 +/- 19 ms) ECGs. There was no significant change in JTc dispersion as well. Thus, JT dispersion is unrelated to QRS duration and unaffected by catheter ablation in patients with Wolff-Parkinson-White syndrome. Eccentric ventricular depolarization does not lead to abnormal dispersion of repolarization.

Effect of heart rate on QT interval in children and adolescents

OBJECTIVE

To study the effect of sympathetic stimulation and increase in heart rate on the QT and QTc intervals.

DESIGN

Prospective non-randomised study of eight consecutive patients.

SETTING

Electrophysiology laboratory at a tertiary centre.

PATIENTS

Eight patients aged 10-20 years (median 12.5) undergoing repeat electrophysiological study after previously successful catheter ablation (n = 6) or presumed supraventricular tachycardia (n = 2) with negative studies.

INTERVENTIONS

Electrocardiograms were obtained (a) at baseline, (b) during atrial pacing at 450 ms cycle length, (c) during isoprenaline infusion at 0.025 microgram/kg/min, (d) adding atrial pacing (450 ms cycle length) to isoprenaline at 0.025 microgram/kg/min, and (e) isoprenaline at 0.05 microgram/kg/min.

MAIN OUTCOME MEASURES

QT and QTc intervals at each of the above mentioned stages.

RESULTS

The QT interval was reduced from a mean value of 350 ms to around 315-325 ms by each of the above manoeuvres. Correspondingly, the QTc increased from a mean of 407 ms to around 445-470 ms. Pacing was as effective as isoprenaline in shortening the QT interval and prolonging the QTc intervals.

CONCLUSIONS

Heart rate directly influences QT and QTc intervals in children and adolescents. The QT is shortened, but QTc is prolonged. Hence, reliance on the QTc alone could lead to mistaken diagnosis of long QT syndrome.