Cardiac Safety Calculator
QTc Calculator for Drug Safety and Clinical Trials
Calculate corrected QT interval using Bazett, Fridericia, Framingham, Hodges, and Rautaharju formulas. Built for drug-induced QT prolongation review, ICH E14 context, and clinical trial cardiac safety monitoring.
Quick Answer
Corrected QT interval (QTc) adjusts the ECG QT interval for heart rate to assess delayed ventricular repolarization and drug-induced arrhythmia risk. ICH E14 guides non-antiarrhythmic drug cardiac safety evaluation, including thorough QT/QTc studies. This calculator computes Bazett, Fridericia, Framingham, Hodges, and Rautaharju QTc values for clinical trial ECG monitoring, concentration-QTc analysis, and medical review of QT-prolonging investigational products.
Fridericia: QTc = QT / RR1/3
Framingham: QTc = QT + 154 × (1 - RR)
Hodges: QTc = QT + 1.75 × (HR - 60)
Rautaharju: QTc = QT - 185 × (RR - 1) + k
Calculate QTc
Enter measured QT and heart rate or RR interval. Fridericia QTc is shown as the primary drug-safety reference.
Primary drug safety reference
- ms
Fridericia QTc is shown as the primary value because it is commonly used in drug safety analysis.
How to Use the QTc Calculator
Worked Example
Input: QT = 400 ms, heart rate = 75 bpm, RR = 60 / 75 = 0.80 seconds.
Bazett: 400 / sqrt(0.80) = 447 ms.
Fridericia: 400 / 0.801/3 = 431 ms.
Interpretation: Fridericia QTc of 431 ms is within common adult reference limits, but interpretation depends on baseline QTc, ECG quality, drugs, electrolytes, and clinical context.
Pharma Context for Clinical Trials
QTc is a core cardiac safety endpoint because drug-induced delay in ventricular repolarization can increase risk for torsades de pointes and other serious arrhythmias. For non-antiarrhythmic investigational products, ICH E14 describes how sponsors evaluate QT/QTc prolongation through thorough QT/QTc (TQT) studies, concentration-QTc (C-QTc) analysis, and routine ECG safety monitoring in later-phase trials.
The pharma-specific need differs from a bedside ECG tool. Sponsors, clinical pharmacologists, medical monitors, and safety teams must prespecify a QT correction formula (often Fridericia), document assay sensitivity in TQT studies with placebo and positive control, and interpret small mean QTc changes against the regulatory 10 ms upper-confidence-bound threshold—not isolated absolute values alone.
QT liability often intersects with exposure. Renal or hepatic impairment can raise drug concentrations and amplify repolarization effects—use our GFR Calculator or Creatinine Clearance Calculator when kidney function affects clearance, and the Dosage Calculator when trial protocols require weight-based or renal-adjusted dosing review alongside ECG safety.
Bazett vs Fridericia vs Framingham vs Hodges
QTc Thresholds and Drug Safety Interpretation
Common reference limits consider QTc prolonged above about 450 ms in males and 460 ms in females. A QTc at or above 500 ms is often treated as a higher-risk threshold, especially when combined with QT-prolonging drugs, hypokalemia, hypomagnesemia, bradycardia, structural heart disease, or large increases from baseline.
Thresholds are not binary safety decisions. In drug development, reviewers look at baseline-corrected change, placebo correction, exposure-response, assay sensitivity, and whether the upper bound of the confidence interval crosses regulatory concern thresholds.
ICH E14 and Thorough QT Context
ICH E14 focuses on the clinical evaluation of QT/QTc prolongation and proarrhythmic potential for non-antiarrhythmic drugs. The guidance is important for thorough QT/QTc studies, cardiac safety ECG collection, and concentration-QTc analysis. It also emphasizes that correction methods should be selected and justified before analysis.
In adults, regulatory Q&A documents note that Bazett is generally an inferior correction method, while Fridericia is likely appropriate in many situations. This calculator shows both so users can compare results and understand formula sensitivity.
Drug-Induced QT Prolongation Risk Factors
- Concomitant QT-prolonging drugs, especially combinations with overlapping risk.
- Electrolyte abnormalities such as hypokalemia, hypomagnesemia, or hypocalcemia.
- Bradycardia, structural heart disease, congenital long QT syndrome, or recent myocardial ischemia.
- High drug exposure from renal impairment, hepatic impairment, drug interactions, or supratherapeutic dosing.
- Oncology, anti-infective, psychiatric, antiemetic, and antiarrhythmic treatment settings where QT liability is common.
Evidence and Regulatory Sources
QTc correction methods, TQT study design, and regulatory concern thresholds are defined in ICH E14 and FDA guidance—not in any single clinical cutoff table. The references below are primary sources for cardiac safety programs, medical monitor training, and protocol authoring.
- FDA: E14 Clinical Evaluation of QT/QTc Interval Prolongation and Proarrhythmic Potential for Non-Antiarrhythmic Drugs
- ICH E14 Guideline (Step 4) — Clinical Evaluation of QT/QTc Interval Prolongation
- ICH E14 Q&A R3 — QT correction methods, TQT design, and concentration-QTc analysis
- FDA ICH E14 implementation guidance hub (QT/QTc evaluation for non-antiarrhythmic drugs)
- CredibleMeds / clinical review: managing drug-induced QT prolongation (evidence summary)
- Competitive landscape: MDCalc Corrected QT Interval (QTc) covers Bazett through Rautaharju with ECG paper-speed options but focuses on ED/cardiology bedside use—not ICH E14 TQT study framing or cardiac safety program context. QT Calculator (Amsterdam LQTS probability tool) adds age/sex LQTS probability from measured QT but is specialized for congenital long QT workup rather than five-formula QTc comparison for investigational drug ECG monitoring. NovaPharmaNews provides free multi-formula QTc with ICH E14/FDA guidance links and cross-links to renal function calculators when clearance affects QT-prolonging drug exposure—no login required.