How to Estimate QT Interval in Patients With Left or Right Bundle Branch Block: A Systematic Review

How to correct QT interval after cardiac resynchronisation therapy

INTRODUCTION

This study evaluates various formulae used to correct the QT interval in patients with wide QRS complexes to calculate corrected QT (QTc) following Cardiac Resynchronisation Therapy (CRT).

METHODS

We included patients with severe heart failure and left bundle branch block, presenting with a QRS duration of at least 120 milliseconds, who underwent successful CRT implantation. Patients were excluded if they had non-lateral left ventricular lead placement, metabolic disorders, atrial fibrillation, atrial tachycardia, or high-degree atrioventricular block prior to implantation. QT intervals were measured pre- and post-implantation and corrected for QRS duration and heart rate using the Boggosian, Wand, Rautaharju, Yankelson, Tang & Rabkin, Bazett, Framingham, Hodges and Fredericia formulae.

RESULTS

A total of 51 patients met the study criteria. After CRT, the QRS duration significantly decreased from 189.68 ± 18.06 milliseconds to 165.25 ± 18.78 milliseconds. However, the QT interval corrected using Bazett's formula showed no significant change (522.30 ± 33.37 milliseconds versus 524.06 ± 36.52 milliseconds). Among the various correction methods, the combination of the Bogossian formula (for QRS duration) followed by the Hodges formula (for heart rate), or the Rautaharju formula followed by the Fredericia formula, produced comparable QT intervals. Similarly, correcting heart rate with the Fredericia formula followed by QRS correction with the Rautaharju formula yielded consistent results.

CONCLUSION

Our findings indicate that different formulae for correcting QT intervals for heart rate and QRS duration may yield varying results. Notably, the use of the Bogossian formula followed by the Hodges formula, or the combination of the Rautaharju and Fredericia formulae, produces relatively consistent QT intervals before and after CRT. Further research is needed to validate these findings.

Antipsychotics and the QTc Interval During Delirium in the Intensive Care Unit: A Secondary Analysis of a Randomized Clinical Trial

Importance

Antipsychotic medications, often prescribed for delirium in intensive care units (ICUs), may contribute to QTc interval prolongation.

Objective

To determine whether antipsychotics increase the QTc interval in patients with delirium in the ICU.

Design, Setting, and Participants

An a priori analysis of a randomized clinical trial in medical/surgical ICUs within 16 centers across the US was conducted. Participants included adults with delirium in the ICU with baseline QTc interval less than 550 ms. The study was conducted from December 2011 to August 2017. Data analysis was performed from April 25 to August 18, 2021.

Interventions

Patients were randomized 1:1:1 to intravenous haloperidol, ziprasidone, or saline placebo administered twice daily until resolution of delirium, ICU discharge, or 14 days.

Main Outcomes and Measures

Twelve-lead electrocardiograms were used to measure baseline QTc before study drug initiation and telemetry was used to measure QTc before each subsequent dose of study drug. Unadjusted day-to-day changes in QTc were calculated and multivariable proportional odds regression was used to estimate the effects of antipsychotics vs placebo on next-day maximum QTc interval, adjusting for prespecified baseline covariates and potential interactions with sex. Safety end points, including the occurrence of torsade de pointes, were evaluated. All analyses were conducted based on the intention to treat principle.

Results

A total of 566 patients were randomized to haloperidol (n = 192), ziprasidone (n = 190), or placebo (n = 184). Median age was 60.1 (IQR, 51.4-68.7) years; 323 were men (57%). Baseline median QTc intervals across the groups were similar: haloperidol, 458.0 (IQR, 432.0-479.0) ms; ziprasidone, 451.0 (IQR, 424.0-472.0) ms; and placebo, 452.0 (IQR, 432.0-472.0) ms. From day 1 to day 2, median QTc changed minimally: haloperidol, -1.0 (IQR, -28.0 to 15.0) ms; ziprasidone, 0 (IQR, -23.0 to 20.0) ms; and placebo, -3.5 (IQR, -24.8 to 17.0) ms. Compared with placebo, neither haloperidol (odds ratio [OR], 0.95; 95% CI, 0.66-1.37; P = .78) nor ziprasidone (OR, 1.09; 95% CI, 0.75-1.57; P = .78) was associated with next-day QTc intervals. Effects were not significantly modified by sex (P = .41 for interaction). There were 2 occurrences of nonfatal torsade de pointes, both in the haloperidol group. Neither was associated with study drug administration.

Conclusions and Relevance

The findings of this trial suggest that daily QTc interval monitoring during antipsychotic use may have limited value in patients in the ICU with normal baseline QTc and few risk factors for QTc prolongation.

Trial Registration

ClinicalTrials.gov Identifier: NCT01211522.

Navigating the pharmacologic complexities of QTc prolongation: assessing the cumulative burden in individuals with serious mental illness

The scientific progress made in the pharmacologic management of serious mental illness (SMI) has been significant. However, the benefits of medication management must continually be weighed against the risks of adverse effects of the agents prescribed. While many medications pose increased danger of QTc prolongation, which may result in malignant arrhythmia and sudden cardiac death, the combination of medications contributing QTc risk can result in an impact of unpredictable pharmacodynamic magnitude. Pharmacists play a key role in communicating QTc risks to prescribers, however little if any clinical guidance informs clinicians of specific actions to take when initiating or continuing a clinically necessary combination that poses risk. This study is a cross-sectional view of Med Safety Scan (MSS) QT prolongation risk scores, generated from the ranking tool available from the CredibleMeds website, intended to provide greater understanding of overall risk of QT burden to assist in the prescribing of medications to patients with SMI in a psychiatric hospital.

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.