- Title
- The half RR rule: a poor rule of thumb and not a risk assessment tool for QT interval prolongation
- Creator
- Berling, Ingrid; Isbister, Geoffrey K.
- Relation
- NHMRC.1061041 & NHMRC 1055176
- Relation
- Academic Emergency Medicine Vol. 22, Issue 10, p. 1139-1144
- Publisher Link
- http://dx.doi.org/10.1111/acem.12752
- Publisher
- Wiley-Blackwell
- Resource Type
- journal article
- Date
- 2015
- Description
- Objectives: Measuring the QT interval on an electrocardiogram (ECG) is integral to risk assessment of Torsade de Pointes (TdP). This study aimed to investigate the accuracy of the 1/2 RR rule as a risk assessment tool for drug-induced TdP, comparing it to the QT nomogram, Bazett's corrected QT (QTcB), and Fridericia's corrected QT (QTcF). Methods: The authors calculated sensitivity and specificity of the 1/2 RR rule using a published data set of 129 cases of drug-induced TdP and 316 controls (noncardiotoxic overdoses), compared to the QT nomogram, QTcB > 500 msec and QTcF > 500 msec. To further determine the value of the 1/2 RR rule, its observed positive, and negative agreement were calculated when compared to the QT nomogram for determining an abnormal QT in eight samples of different drugs in overdose. Results: The sensitivity and specificity of the 1/2 RR rule were 88% (95% confidence interval [CI] = 80% to 93%) and 53% (95% CI = 47% to 58%), respectively, compared to the QT nomogram (sensitivity = 97%, 95% CI = 92% to 99%; specificity = 99%, 95% CI = 97% to 100%). It was also less sensitive than QTcB > 500 msec and had a lower specificity than QTcB > 500 msec and QTcF > 500 msec. In drug overdose patients, the 1/2 RR rule had poor observed agreement averaging 41%, which was mainly due to poor positive agreement, except for amisulpride where there was good agreement. Conclusions: The 1/2 RR rule was not as sensitive as the QT nomogram or QTcB > 500 msec for drug-induced TdP. It had poor positive agreement in almost all overdose patients, resulting in over half of patients receiving unnecessary cardiac monitoring and repeat ECGs.
- Subject
- Torsade de Pointes (TdP); QT interval prolongation; 1/2 RR rule; electrocardiogram (ECG)
- Identifier
- http://hdl.handle.net/1959.13/1314375
- Identifier
- uon:22759
- Identifier
- ISSN:1069-6563
- Language
- eng
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