In this episode, I’ll discuss whether the Tisdale Risk Score can be used to identify ICU patients at risk of QTc prolongation.
The Tisdale Risk Score (TRS) was first published in 2013 as a way to identify hospitalized patients at risk for QT interval prolongation. The scoring system assigns points based on age, sex, diuretic use, serum potassium, admission QTc, acute MI, heart failure or sepsis diagnoses, and the number of QTc prolonging medications a patient is receiving. Based on the number of points the patient is said to be at low, medium, or high risk of QTc prolongation. A high-risk score was associated with a sensitivity of 74%, a specificity of 77%, a positive predictive value of 0.79, and a negative predictive value of 0.76.
An advantage of this scoring system is that it uses clinical values that are easily obtained from the medical record and it is practical to perform. One drawback of this scoring system is that the cohort of patients used for validation was entirely cardiac care unit patients.
The authors of a recent study published in Pharmacotherapy sought to evaluate the usefulness of the TRS in a medical ICU.
A sample size of 264 medical ICU patients was used for this validation. The first occurrence of QTc interval prolongation, defined as a QTc interval >500ms or an increase ≥60ms above baseline, was the primary endpoint.
The TRS appeared to overestimate QTc risk in the medical ICU population as the specificity was very low at just 16%. However, when the low-risk group was compared to the moderate and high-risk groups, the TRS had a sensitivity of 97%. This indicates that the TRS could be used to identify a cohort of patients at low risk for QTc prolongation.
One interesting point of agreement between the CCU and ICU cohorts is that sepsis was identified in both groups as a risk factor for QTc prolongation.
Neither the CCU or ICU cohort were powered to detect the rare event of torsades, so QTc prolongation was used as a surrogate risk factor to the actual clinical risk to the patient.
I have created a calculator on this page to easily determine the Tisdale Risk Score.
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