Multiple logistic regression
Our preliminary risk score had an area under the Receiver Operating
Characteristic (ROC)-curve of 0.848 to predict a QTc ≥ 450 ms for males,
≥ 470 ms for females, or an increase from baseline ECG by ≥ 30 ms. The
results of the multiple logistic regression are displayed in table 3.
Significant p-values are shown in bold.
Panel A includes the full dataset of all components in our preliminary
score, whereas panel B includes the components after exclusion of
selected insignificant or unimportant factors.
In the full dataset, significant risk factors included age ≥ 65 years,
female sex, ischemic cardiomyopathy and/or hypertension, arrhythmia,
potassium ≤ 3.5 mmol/L, CRP > 5 mg/L, drugs from
CredibleMeds list 1 and 2. After excluding BMI ≥ 30
kg/m2, liver failure, diabetes, neurological disease,
CRP > 5 mg/L, eGFR ≤ 30 ml/min, and drugs from CredibleMeds
list 3, panel B logistic regression resulted in similar significant
factors, except for arrhythmia which was shown to be no longer
significant. However, we decided to keep it in our risk score because we
believed it would largely determine the risk for QTc prolongation.
Although the CRP component was shown to be significant in our full
dataset, we excluded it from panel B after discussions with cardiology,
with the notion that most patients at our institution have elevated CRP
values. We retained calcium and thyroid disturbances in the updated
dataset since many patients with QTc-prolongation had low calcium levels
and thyroid disorders.
Table 3. Results of the multiple logistic regression