QTc interval evaluation in patients with right bundle branch block or bifascicular blocks

QTc interval measurement in patients with right bundle branch block: A practical method

BACKGROUND AND AIM

Prolonging the QT interval in the right bundle branch block (RBBB) can create challenges for electrophysiologists in estimating repolarization time and eliminating the effect of depolarization changes on QT interval. In this study, we aimed to develop a practice formula to eliminate the effect of depolarization changes on QT interval in patients with RBBB.

METHODS

This prospective study evaluated accidentally induced RBBB in patients undergoing electrophysiological study. Two expert electrophysiologists recorded the ECG parameters, including QRS duration, QT interval, and cycle length, in the patients. The formula was developed based on QT interval differences (with and without RBBB) and its proportion to QRS. Additionally, the Bazzet, Rautaharju, and Hodge formulas were used to evaluate QTc.

RESULTS

We evaluated 96 patients in this study. The mean QT interval without RBBB was 369.39 ± 37.38, reaching 404.22 ± 39.23 after inducing RBBB. ΔQT was calculated as 34.83 ± 17.61, and the ratio of ΔQT/QRS with RBBB was almost 23%. Our formula is: (QT_{with RBBB}  - 23% × QRS). Subtraction of 25% instead of 23% seems more straightforward and practical. Our formula could also predict the QTc interval in RBBB based on the Bazzet, Rautaharju, and Hodge formulas.

CONCLUSION

Previous formulas for QT correction were hard to apply in the clinical setting or were not specified for RBBB. Our new formula allows a rapid and practical method for QT correction in RBBB in clinical practice.

Determinants of severe QTc prolongation in a real-world gerontopsychiatric setting

Introduction

QT_c prolongation carries the risk of ventricular tachyarrhythmia (Torsades de Pointes) and sudden cardiac death. Psychotropic drugs can affect ventricular repolarization and thus prolong the QT_c interval. The present study sought to investigate the risk factors (pharmacological and non-pharmacological) of severe QT_c prolongation in gerontopsychiatric patients.

Methods

Electrocardiograms of patients on a gerontopsychiatric ward were screened for QT_c prolongation. Medication lists were examined utilizing the AzCERT classification. Potential drug interactions were identified with the electronic drug interaction program mediQ.

Results

The overall prevalence of QT_c prolongation was 13.6%, with 1.9% displaying severe QT_c prolongation (≥ 500 ms). No statistically significant differences between patients with moderate and severe QT_c prolongation were identified; however, patients with severe QT_c prolongation tended to take more drugs (p = 0.063). 92.7% of patients with QT_c prolongation took at least one AzCERT-listed drug, most frequently risperidone and pantoprazole. Risperidone and pantoprazole, along with pipamperone, were also most frequently involved in potential drug interactions. All patients displayed additional risk factors for QT_c prolongation, particularly cardiac diseases.

Conclusion

In addition to the use of potentially QT_c-prolonging drugs, other risk factors, especially cardiac diseases, appear to be relevant for the development of QT_c prolongation in gerontopsychiatric patients. Pantoprazole was frequently involved in potential drug interactions and should generally not be used for more than 8 weeks in geriatric populations. As clinical consequences of QT_c prolongation were rare, potentially QT_c-prolonging drugs should not be used overcautiously; their therapeutic benefit should be considered as well. It is paramount to perform diligent benefit-risk analyses prior to the initiation of potentially QT_c-prolonging drugs and to closely monitor their clinical (side) effects.

Estimation of the QTc interval in the presence of right bundle branch block: A comparative study using validated formulae for left bundle branch block

BACKGROUND

Adequate measurement of the QT interval is of clinical importance in order to identify patients at higher risk for ventricular arrhythmias. Previous studies have described different methods to estimate baseline QT in patients with left bundle branch block (LBBB). However, the evidence regarding the assessment of the QT in patients with right bundle branch block (RBBB) is scarce.

AIM

To analyze the feasibility and reliability of the different formulae described for LBBB in the estimation of the baseline QT in the presence of RBBB.

METHODS

We performed an observational study including patients who underwent electrophysiology study and/or ablation. Two types of RBBB were considered: 1) pacing-induced and 2) transient true RBBB. QRS, JT and QT intervals were measured during baseline and RBBB. Estimated QTc was calculated using LBBB formulae: Bogossian, Rautaharju, Tabatabaei, Tang-Rabkin, Yankelson, Wang. Linear correlation and intraclass correlation coefficients (ICC) were used to assess the reliability of these formulae for the estimation of baseline QTc.

RESULTS

We finally included a total of 100 patients. Correlations between baseline and estimated QTc were strong (R > 0.7) for all the formulae except for Tabatabaei. Yankelson and Wang showed the highest reliability (ICC = 0.775 and 0.727, respectively). Yankelson appeared to be the most accurate formula, with a mean estimated QTc closest to baseline values.

CONCLUSION

Previously described formulae for LBBB exhibited marked differences regarding reliability in the estimation of the QTc interval in the presence of RBBB. According to our results, Yankelson showed the most consistent and accurate agreement in this setting.

Assessment of the QT interval in right bundle branch block

BACKGROUND

Identifying prolonged QT interval in RBBB has been problematic.

METHODS

Four approaches were compared to adjust for the QT prolongation in intermittent RBBB. The implications were assessed in a separate group of 200 persons with established RBBB.

RESULTS

In 12 individuals, mean age 74.5 years with intermittent RBBB, the presence of RBBB significantly (p < 0.05) increased the QT interval in each of six different heart rate correction formulae by an amount ranging from 35.4 ms in the Hodges formula to 50.2 ms in the Bazett formula. Four different equations were tested to adjust the QT interval and one approach QTc_RBBB = 0.945*QTc_RBBB - 26 was the best method to adjust for the increased QT in RBBB as it produced a QT value that was not significantly different from the QT interval in the absence of RBBB in intermittent RBBB.Failure to adjust the QT interval in RBBB produces an overestimate of the QT interval which in some heart rate adjustment formulae was marked. For the Bazett heart rate adjustment approach QTc 450 ms was found in 73.9% of men and QTc over 460 ms was found in 60.6% of women.

CONCLUSION

These data suggest the implementation of a new approach to recalculate the QT intervals in RBBB. QTc_RBBB = 0.945*QTc_RBBB - 26 with an appropriate heart rate adjustment formula (other than the Bazett formula) accurately predicts the QT interval in the absence of RBBB.

Assessment of QTc and Risk of Torsades de Pointes in Ventricular Conduction Delay and Pacing: A Review of the Literature and Call to Action

BACKGROUND

Assessment of the heart rate-corrected QT-interval on the 12-lead electrocardiogram when prescribing medications known to increase the risk of Torsades de Pointes has become a common part of consultation-liaison psychiatry practice.

OBJECTIVES

Highlighted by a patient who experienced psychiatric decompensation due to inaccurate interpretation of QTc prolongation in the setting of a wide QRS complex, we aimed to describe the approach to QTc interpretation in patients with ventricular conduction delay.

METHODS

We reviewed the current literature on the approach to assessment of prolonged repolarization in patients with ventricular conduction delay due to bundle branch block (BBB) and ventricular pacing.

RESULTS

Physicians of any specialty may perform initial electrocardiogram interpretation and should be proficient in the definition, recognition, and understanding of the basic pathophysiology of electrocardiographic abnormalities. We discuss current approaches to assessment of the QT-interval in patients with a wide QRS complex due to bundle branch block and ventricular pacing, including bivariate QTc modification, univariate QT-interval modifications, and use of the JT-interval.

CONCLUSIONS

The QT-interval is prolonged ipso facto in patients with a wide QRS complex from ventricular conduction delay/ventricular pacing and must be adjusted for QRS duration. Multiple formulae have been proposed to account for wide QRS complex in this setting with no single universally accepted methodology. We suggest the use of either the Bogossian formula or JT-interval followed by Hodges or Framingham heart-rate correction to adjust for a wide QRS complex. It is critical that the C-L psychiatrist be able to identify a wide QRS complex on the electrocardiogram, understand implications for accurate assessment of prolonged depolarization, and apply an appropriate correction methodology.

Spotlight: Wie bestimmt man das QTc-Intervall richtig?

Das EKG stellt eine der wichtigsten nicht invasiven Untersuchungsmethoden dar. Im klinischen Alltag bietet es einen hohen Informationsgehalt bei sehr geringen Kosten. Nichtsdestotrotz ist die EKG-Interpretation für viele Ärzte herausfordernd. Selbst bei einem normalen EKG bedarf es ausreichender Sorgfalt, um die einzelnen Zeitintervalle ordentlich zu vermessen. Deutlich schwieriger wird die Interpretation beim Auftreten von Herzrhythmusstörungen. Hier müssen dann (wie z. B. beim Vorhofflimmern) mehrere Messungen durchgeführt und berücksichtigt werden, um das QT-Intervall korrekt zu beurteilen. Weitere EKG-Veränderungen können die Messung und Interpretation der QT-Zeit weiter beeinflussen. So kommt insbesondere bei Frequenzvariabilität (Tachykardien/Bradykardien) und beim Auftreten von Schenkelblockierungen die Anwendung diverser Formeln zum Tragen. Erst nach Berücksichtigung all dieser Aspekte kann eine ordentliche Messung und Interpretation der QTc-Zeit erfolgen.

QTc evaluation in patients with bundle branch block

Proper measurement of the QT interval on the 12-lead body-surface ECG is challenging in daily practice. Even more difficult is its correct estimation in the presence of repolarization abnormalities, arrhythmias or bundle-branch blocks (BBB). The QT interval results from two parts of the ECG: (1) the QRS complex, describing the excitation of the ventricles and (2) the JT interval, describing the repolarisation of the ventricles. Prolongation of the QRS width – like in the presence of BBB – entails prolongation of the QT interval, making the estimation of the true repolarisation time challenging. The US recommendations for the standardization and interpretation of the ECG suggest focusing on the JT interval in presence of BBB. However, in clinical practice physicians have become more familiar with the interpretation of QT-interval measurements than with the interpretation of the JT Interval.

In the last decade, a simple formula for the estimation of the “modified QT interval” in the presence of left or right BBB has been developed and evaluated. In this formula, the modified QT interval is calculated by subtracting 50% of the length of the BBB-QRS from the measured QT interval (QT_m = QT_BBB − 50% QRS_BBB). Subsequently, rate-correction formula should be applied as usual. In this review, we discuss the determination of the QT-interval in the presence of BBB and summarize the origin and application of the modified QT-interval formula.

QTc interval evaluation in patients with right bundle branch block or bifascicular blocks

BACKGROUND

The right bundle branch block (RBBB) and the bifascicular blocks affect QRS duration in the right precordial leads, which are usually used for QT interval determination. Up to now, there is no clear recommendation how to determine QT interval in patients with RBBB or bifascicular block.

HYPOTHESIS

The hypothesis of the present study was to evaluate the feasibility of a simple formula for RBBB and bifascicular block correction, thereby making it easier to determine the QTc interval.

METHODS

In patients with intrinsic QRS duration <120 ms, artificial RBBB with either left posterior (LPFB) or left anterior fascicular block (LAFB), created by left ventricular pacing maneuvers, were corrected using the Bogossian formula (QTm) and afterward were heart rate corrected (QTmc). Heart rate correction was performed using different heart rate formulas in comparison to each other. The QTmc intervals were compared in each patient with the QTc interval during intrinsic rhythm.

RESULTS

A total of scheduled 71 patients were included in this prospective multicenter observational comparative study. Compared to intrinsic QTc interval, the mean ΔQTmc interval by combination of the Bogossian and the Hodge formulas was -3 ± 24 ms in RBBB + LPFB (P = .44) and -6 ± 25 ms in RBBB + LAFB (P = .15). The Bogossian formula showed a significant deviation from the actual QTc interval with both the Bazett and the Fridericia formulas.

CONCLUSION

In combination with the Hodge formula, the Boggosian formula delivered the best results in comparing the true QTc interval in narrow QRS with the QTmc interval in the presence of a bifascicular block.