The Half RR Rule: A Poor Rule of Thumb and Not a Risk Assessment Tool for QT Interval Prolongation

Risk assessment tools for QT prolonging pharmacotherapy in older adults: a systematic review

Purpose

Many drugs are associated with the risk of QT prolongation and torsades de pointes (TdP), and different risk assessment tools (RATs) are developed to help clinicians to manage related risk. The aim of this systematic review was to summarize the evidence of different RATs for QT prolonging pharmacotherapy.

Methods

A systematic review was conducted using PubMed and Scopus databases. Studies concerning risk assessment tools for QT prolonging pharmacotherapy, including older adults, were included. Screening and selection of the studies, data extraction, and risk of bias assessment were undertaken.

Results

A total of 21 studies were included, involving different risk assessment tools. Most commonly used tools were risk scores (n = 9), computerized physician order entry systems (n = 3), and clinical decision support systems (n = 6). The tools were developed mainly for physicians and pharmacists. Risk scores included a high number of risk factors, both pharmacological and non-pharmacological, for QT prolongation and TdP. The inclusion of patients’ risk factors in computerized physician order entry and clinical decision support systems varied.

Conclusion

Most of the risk assessment tools for QT prolonging pharmacotherapy give a comprehensive overview of patient-specific risks of QT prolongation and TdP and reduce modifiable risk factors and actual events. The risk assessment tools could be better adapted to different health information systems to help in clinical decision-making. Further studies on clinical validation of risk assessment tools with randomized controlled trials are needed.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00228-022-03285-3.

A Practical Method for QTc Interval Measurement

Objective The various formulae used for QT correction by heart rate (HR) require the execution of operations with the aid of calculators or applications. This study aimed to evaluate the performance of a simple rule for QTc estimation, comparing the measurements obtained with those provided by the commonly used equations of Bazett, Fridericia, Framingham, and Hodges. Methods We used the database of a previous observational study, which analyzed patients prospectively with acute pulmonary edema admitted in an emergency service. One hundred four patients were included for QTc assessment, of whom 86 patients underwent two ECG: one ECG <24h and other >24h after admission. Thus, a total of 190 ECGs were analyzed by two observers that manually measured QT and HR. QTc was obtained using the known formulae and the proposed equations: QTc = QT+2 (FC-60) for HR ≤ 90 bpm and QTc=QT+2(FC-60)-10 for HR>90 bpm. Results Bland-Altman plots show good agreement between the simple rule and Hodges equation, with a mean difference of -3,4, SD of 4.96 and 95% limits of agreement from -9,9 to 3.2. There was not a good agreement between the simple method and the other formulae. Conclusion The proposed method has good agreement with the measures of QTc by the equation of Hodges in the HR range of 40 to 130bpm in acutely ill patients. Our method may be a plausible option for quick QT correction in these subjects.

Pseudo-colouring an ECG enables lay people to detect QT-interval prolongation regardless of heart rate

Drug-induced long QT syndrome (diLQTS), characterized by a prolongation of the QT-interval on the electrocardiogram (ECG), is a serious adverse drug reaction that can cause the life-threatening arrhythmia Torsade de Points (TdP). Self-monitoring for diLQTS could therefore save lives, but detecting it on the ECG is difficult, particularly at high and low heart rates. In this paper, we evaluate whether using a pseudo-colouring visualisation technique and changing the coordinate system (Cartesian vs. Polar) can support lay people in identifying QT-prolongation at varying heart rates. Four visualisation techniques were evaluated using a counterbalanced repeated measures design including Cartesian no-colouring, Cartesian pseudo-colouring, Polar no-colouring and Polar pseudo-colouring. We used a multi-reader, multi-case (MRMC) receiver operating characteristic (ROC) study design within a psychophysical paradigm, along with eye-tracking technology. Forty-three lay participants read forty ECGs (TdP risk n = 20, no risk n = 20), classifying each QT-interval as normal/abnormal, and rating their confidence on a 6-point scale. The results show that introducing pseudo-colouring to the ECG significantly increased accurate detection of QT-interval prolongation regardless of heart rate, T-wave morphology and coordinate system. Pseudo-colour also helped to reduce reaction times and increased satisfaction when reading the ECGs. Eye movement analysis indicated that pseudo-colour helped to focus visual attention on the areas of the ECG crucial to detecting QT-prolongation. The study indicates that pseudo-colouring enables lay people to visually identify drug-induced QT-prolongation regardless of heart rate, with implications for the more rapid identification and management of diLQTS.

Measurement and Management of QT Interval Prolongation for General Physicians

One of the more challenging aspects of ECG interpretation is measurement and interpretation of the QT interval. This interval represents the time taken for the ventricles to completely repolarise after activation. Abnormal prolongation of the QT interval can lead to torsades de pointes, a form of potentially life-threatening polymorphic ventricular tachycardia (VT). Detection of a prolonged QT interval is essential as this can be a reversible problem, particularly in the context of the use of a variety of commonly prescribed medications in the hospital setting. Automated ECG printouts cannot be relied upon to diagnose QT interval prolongation; thus, the onus is on the clinician to identify it. This is a difficult task, as the normal QT interval is typically measured relative to the heart rate. Therefore, the QT interval often requires "correction" for the current heart rate, in order to correctly stratify the risk of torsades de pointes. A wealth of correctional formulae have been derived, but none has proven superior. We present an approach to the ECG in this context, and a step-by-step guide to manually measuring and correcting the QT interval, and an approach to management in common hospital-based clinical scenarios.

Screening for QT Prolongation in the Emergency Department: Is There a Better "Rule of Thumb?"

Introduction

Identification of QT prolongation in the emergency department (ED) is critical for appropriate monitoring, disposition, and treatment of patients at risk for torsades de pointes (TdP). Unfortunately, identifying prolonged QT is not straightforward. Computer algorithms are unreliable in identifying prolonged QT. Manual QT-interval assessment methods, including QT correction formulas and the QT nomogram, are time-consuming and are not ideal screening tools in the ED. Many emergency clinicians rely on the “rule of thumb” or “Half the RR” rule (Half-RR) as an initial screening method, but prior studies have shown that the Half-RR rule performs poorly as compared to other QT assessment methods. We sought to characterize the problems associated with the Half-RR rule and find a modified screening tool to more safely assess the QT interval of ED patients for prolonged QT.

Methods

We created graphs comparing the prediction of the Half-RR rule to other common QT assessment methods for a spectrum of QT and heart rate pairs. We then proposed various modifications to the Half-RR rule and assessed these modifications to find an improved “rule of thumb.”

Results

When compared to other methods of QT correction, the Half-RR rule appears to be more conservative at normal and elevated heart rates, making it a safe initial screening tool. However, in bradycardia, the Half-RR rule is not sufficiently sensitive in identifying prolonged QT. Adding a fixed QT cutoff of 485 milliseconds (ms) increases the sensitivity of the rule in bradycardia, creating a safer initial screening tool.

Conclusion

For a rapid and more sensitive screening evaluation of the QT interval on electrocardiograms in the ED, we propose combining use of the Half-RR rule at normal and elevated heart rates with a fixed uncorrected QT cutoff of 485 ms in bradycardia.

Monitoring the corrected QT in the acute care setting: A comparison of the 12‑lead ECG and bedside monitor

INTRODUCTION

Prolongation of the QT interval is a well-recognized complication associated with many commonly used medications. Emergency Department monitoring of the corrected QT (QTc) both before and after medication administration is typically performed using the 12‑lead electrocardiogram (ECG). The purpose of this study is to compare the QTc reported on the 12‑lead ECG to that reported by single brand of bedside monitor.

METHODS

A convenience sample of emergency department patients over the age of 18 undergoing bedside monitoring and who had an ECG ordered by their treating physician were enrolled. These patients underwent simultaneous ECG and monitor QTc calculation. The primary outcome of interest was the correlation between the monitor and ECG QTc. Secondary outcomes included ability of each method to identify patients with a QTc >500ms and the ability of each method to identify patients with a QTc <450ms.

RESULTS

A total of 125 patients had simultaneous ECG and monitor QTc measurements recorded. There was moderate correlation between the monitor and ECG QTc (Pearson's correlation coefficient=0.55). The median difference between the ECG QTc and the monitor QTc (ECG QTc minus monitor QTc) was -7ms (IQR -23 to 11ms).

CONCLUSION

We found that there was moderate correlation between the QTc reported on the 12 lead ECG and that reported by the bedside monitor. This correlation is not strong enough to support the use of the bedside monitor as a substitute for the 12‑lead ECG when evaluating a patient's QTc.

A review of ECG and QT interval measurement use in a public psychiatric inpatient setting

OBJECTIVES

There is an increased rate of sudden cardiac death (SCD) in mental health patients. Some antipsychotic medications are known to prolong the QT interval, thus increasing a patient's risk of SCD via the arrhythmia, torsades de pointes (TdP). Our aim was to evaluate assessment for QT prolongation within a public inpatient mental health facility by auditing electrocardiograph (ECG) use.

METHODS

We reviewed records of all mental health inpatient admissions to a public emergency mental health inpatient unit between 1 January 2016 and 11 February 2016. ECG availability was noted and QT interval was manually measured and assessed for risk of TdP using the QT nomogram when present. Demographic information and medication use was collected.

RESULTS

Of 263 mental health inpatient admissions, 50 (19%) presentations had an ECG. A total of four (8%) had a prolonged QT interval. Of the 50 patients with an ECG, 12 (24%) were taking medication known to prolong the QT interval.

CONCLUSIONS

There was very limited risk assessment for QT prolongation in a public hospital psychiatric inpatient unit, with less than 20% of patients having an ECG performed. Our study supports an association between QT-prolonging drugs and a clinically significant prolonged QT interval; however, a larger study with routine ECG screening is required.

QT interval prolongation in opioid agonist treatment: analysis of continuous 12-lead electrocardiogram recordings

AIMS

Methadone is a widely used opioid agonist treatment associated with QT prolongation and torsades de pointes. We investigated the QT interval in patients treated with methadone or buprenorphine using continuous 12-lead Holter recordings.

METHODS

We prospectively made 24-h Holter recordings in patients prescribed methadone or buprenorphine, compared to controls. After their normal dose a continuous 12-lead Holter recorder was attached for 24 h. Digital electrocardiograms were extracted hourly from the Holter recordings. The QT interval was measured automatically (H-scribe software, Mortara Pty Ltd) and checked manually. The QT interval was plotted against heart rate (HR) on the QT nomogram to determine abnormality. Demographics, dosing, medical history and laboratory investigations were recorded.

RESULTS

There were 58 patients (19 methadone, 20 buprenorphine and 19 control); median age 35 years (20-56 years); 33 males. Baseline characteristics were similar. Median dose of methadone was 110 mg day-1 (70-170 mg day-1 ) and buprenorphine was 16 mg day-1 (12-32 mg day-1 ). Seven participants had abnormal QT intervals. There was a significant difference in the proportion of prescribed methadone with abnormal QT intervals, 7/19 (37%; 95% confidence interval: 17-61%), compared to controls 0/19 (0%; 95% confidence interval: 0-21%; P = 0.008), but no difference between buprenorphine and controls (0/20). QT vs. HR plots showed patients prescribed methadone had higher QT-HR pairs over 24 h compared to controls. There was no difference in dose for patients prescribed methadone with abnormal QT intervals and those without.

CONCLUSIONS

Methadone is associated with prolonged QT intervals, but there was no association with dose. Buprenorphine did not prolong the QT interval. Twenty four-hour Holter recordings using the QT nomogram is a feasible method to assess the QT interval in patients prescribed methadone.