Corrected QT interval and corresponding risk of torsades de pointes in drug-induced QT prolongation

This risk tool accurately predicts torsade de pointes (TdP) risk for drug-induced QT prolongation, allowing users to select the desired sensitivity and specificity for detecting torsades des points using different cut-offs:

Cut-off 1 (Bazett's QTc = 500 ms): By selecting this cut-off value, the calculator will have a sensitivity and specificity of 93.8% and 97.2% in detecting torsades des pointes, respectively. This setting aims at reducing the probability of unnecessary cardiac monitoring as much as possible.

Cut-off 2 (Bazett's QTc = 440 ms): By selecting this cut-off value, the calculator will have a sensitivity and specificity of 98.5% and 66.7% in detecting torsades de points, respectively. This setting aims at reducing the risk of missing torsades des points as much as possible.

Research authors: Chan A, Isbister GK, Kirkpatrick CM, and Dufful SB.

Version: 1.39

Public
Cardiology
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Corrected QT interval based on Bazett's formula:

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Corrected QT interval based on Bazett's formula: ms

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Context information:
The aim of the underlying study was to evaluate the performance of the QT nomogram in assessing the risk of TdP, comparing QT-heart rate combinations for known cases of drug-induced TdP cases to those of a negative control group with normal QT-HR values.

Source:
Chan A, Isbister GK, Kirkpatrick CM, Dufful SB. Drug-induced QT prolongation and torsades de pointes: evaluation of a QT nomogram. QJM. 2007;100(10):609-15.

This algorithm is provided for educational, training and information purposes. It must not be used to support medical decision making, or to provide medical or diagnostic services. Read our full disclaimer.

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Details

Algorithm author

Evidencio Community

Algorithm ID

1418

Version

1.39.{{ model.microversion }}

Revision date

2019-05-13

Specialty

Cardiology , Clinical pharmacology , Intensive care , Internal medicine

Algorithm type

Custom calculation ^{(Calculation)}

MeSH terms

Long QT Syndrome

Torsades de Pointes

Cardiac Arrhythmias

Status

Public

Formula

Study characteristics

Additional information

DESIGN:
Systematic review.

METHODS:
We systematically searched MEDLINE/EMBASE for cases of drug-induced TdP. Controls were patients taking non-cardiotoxic drugs in overdose. Inclusion criteria were definite TdP, normal ECG before or after the event, association with a drug/toxin and QT-RR measurements available. The upper bound of a QT-RR cloud diagram developed from human preclinical studies was converted into a QTnomogram [QT vs. heart rate (HR)]. QT-HR combinations for TdP cases and controls were plotted with the QT nomogram, and curves corresponding to a QTc = 440 ms and QTc = 500 ms for comparison (Bazett's correction).

RESULTS:
We identified 129 cases of TdP. TdP cases occurred at lower HR values with longer QT intervals, with most cases occurring at HR 30-90 bpm. Controls were more evenly distributed, with HR 40-160 bpm. The sensitivity and specificity of the QT nomogram were 96.9% (95%CI 93.9-99.9) and 98.7% (95%CI 96.8-100), respectively. For Bazett QTc = 440 ms, sensitivity and specificity were 98.5% (95%CI 96.3-100) and 66.7% (95%CI 58.6-74.7), respectively, whereas for Bazett QTc =500 ms they were 93.8% (95%CI 89.6-98.0) and 97.2% (95%CI 94.3-100), respectively.

DISCUSSION:
The QT nomogram is a clinically relevant risk assessment tool that accurately predicts arrhythmogenic risk for drug-inducedQT prolongation. Further prospective evaluation of the nomogram is needed.

Study Population

Total population size: 129

Continuous characteristics

Name	LL	Q1	Median	Q3	UL	Unit
Age	10	36	53	68	95	years

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