Tisdale Risk Score for QT Prolongation

Tisdale scale, online calculator, calculator, QT, QT prolongation, QT prolongation, QT interval, tachycardia, pirouette tachycardia, Torsade de pointes, TdP, polymorphic ventricular tachycardia

Tisdale Risk Score for QT Prolongation predicts risk of QT prolongation greater than 500 msec in hospitalized patients.

QT interval prolongation increases the risk of Torsade de pointes (TdP), a type of polymorphic ventricular tachycardia which is life-threatening and often fatal.

Age ≥68 years:
Yes
No

Sex:
Male
Female

Patient on loop diuretic:
Yes
No

Potassium ≤3.5 mEq/L (mmol/L). (Potassium should be potassium determined closest to EСG timing):
Yes
No

Admission QTc ≥450 msec (QTc – corrected QT interval (relative to heart rate):
Yes
No

Being admitted for acute myocardial infarction:
Yes
No

Being admitted for sepsis:
Yes
No

Being admitted for heart failure:
Yes
No

Number of QTc-prolonging drugs given:
None
1 QTc-prolonging drug
≥2 QTc-prolonging drugs


Tisdale Risk Score Risk for QT prolongation Clinical recommendation
0 0 0

Many hospitalized patients have increased risk of QT prolongation due to medical conditions they are facing (myocardial infarction, sepsis, heart failure with reduced enjection fraction for example), as well as medications they may be prescribed in order to treat these conditions (antibiotics, antivirals, antifungals, or anti-arrhythmics, for example) or continue outpatient medications (like psychotropic medications, methadone, or tamoxifen, for example).

This risk score can assess risk of QT prolongation for a physician or pharmacist managing a patient in the hospital.

  • There are many known factors that can cause the risk of QT prolongation; the ones included in this score were found to be the most predictive, but others should not be ignored. Some of the other common risks include:
    • Other electrolyte abnormalities like hypomagnesemia or hypocalcemia
    • Inadequate dose adjustment for patients with acute or chronic kidney dysfunction
    • Drug-drug interactions
  • CredibleMeds.org also provides a comprehensive list of drugs that may cause QT prolongation.
  • Drug-drug interactions should always be considered when prescribing multiple medications; this score does not include pharmacokinetic drug interactions.
  • This score also does not consider dosing adjustments for renally-eliminated drugs.
  • Clinicians should always try to avoid QT-prolonging medications when possible.
  • Maintaining normal electrolyte levels can help reduce the risk of QT prolongation as well.
  • Patients with very poor ejection fractions (<20%) are particularly high risk for QT prolongation.

Tisdale Risk Score for QT Prolongation. Addition of the selected points*:

Risk factorPoints
Age ≥68 years1
Gender: Female1
The use of loop diuretics1
Potassium in blood plasma ≤3.5 mmol / l2
Admission QTc** ≥450 msec2
Acute myocardial infarction**2
Heart failure with low PV3
1 drug that prolongs the QTc interval ***3
≥2 drugs that prolong the QTc interval **3
Sepsis**3
Maximum score21

* Risk categories: low risk = <7; moderate risk = 7-10; high risk = ≥11.
** During an acute event / illness; as a rule, the QTc interval returns to normal after the condition is cured. *** Three points for taking 1 drug that prolongs the QTc interval; 3 additional points for taking ≥2 drugs that prolong the QTc interval (a total of 6 points).

Interpretation:

Tisdale Risk ScoreRisk for QT prolongationRecommendation
≤6LowAlways consider that higher risk may develop depending on clinical course and drug interactions and pharmacokinetics.
7-10ModerateConsider consultation with pharmacist, adjusting risk factors as much as possible. EKG should be repeated after 5 half-lives of QT-prolonging drugs given to evaluate QTc. 
≥11HighConsider consultation with pharmacist, adjusting risk factors as much as possible, and using alternative medications if possible. EKG should be repeated after 5 half-lives of QT-prolonging drugs given to evaluate QTc. 

ECG should be repeated 8-12 hours after starting QT-prolonging drug to look for signs of QT prolongation, with closer monitoring if it is observed.

Correct electrolyte abnormalities and maintain serum potassium >4.0 mEq/L and serum magnesium >2.0 mg/dL.

This scale was launched during COVID-19 crisis. 

This score was derived and internally validated for hospitalized patients, and may not predict outpatient risk of QT prolongation as accurately (but has not been studied in this population).

LITERATURE:
Tisdale JE, Jaynes HA, Kingery JR, et al. Development and validation of a risk score to predict QT interval prolongation in hospitalized patients. Circ Cardiovasc Qual Outcomes. 2013;6(4):479-87. https://pubmed.ncbi.nlm.nih.gov/23716032/
Tisdale JE, Jaynes HA, Kingery JR, et al. Effectiveness of a clinical decision support system for reducing the risk of QT interval prolongation in hospitalized patients [published correction appears in Circ Cardiovasc Qual Outcomes. 2014 Nov;7(6):981]. Circ Cardiovasc Qual Outcomes. 2014;7(3):381-390. doi:10.1161/CIRCOUTCOMES.113.000651  https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4696749/
Tisdale JE. Drug-induced QT interval prolongation and torsades de pointes: Role of the pharmacist in risk assessment, prevention and management. Can Pharm J (Ott). 2016;149(3):139-152. doi:10.1177/1715163516641136 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4860751/

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