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.
Details Formula Study characteristics Files & References
★★★
Model author
Model ID
1418
Version
1.39
Revision date
2019-05-13
MeSH terms
  • Long QT Syndrome
  • Torsades de Pointes
  • Cardiac Arrhythmias
  • Model type
    Custom model (Calculation)
    Status
    public
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    Formula

    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

    Corrected QT interval based on Bazett's formula:
    ...
    ms

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    Result
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    Corrected QT interval based on Bazett's formula: ms

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    Outcome stratification

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    Conditional information

    Result interpretation

    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.

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    Calculations alone should never dictate patient care, and are no substitute for professional judgement. See our full disclaimer.

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