QTc Calculator
Calculate corrected QT interval using multiple formulas for cardiac arrhythmia risk assessment
Calculate Corrected QT Interval
Normal: 300-450 ms (varies with heart rate)
Normal: 60-100 bpm
Different normal ranges for males and females
QTc Results
Primary formula (Bazett): QTc = QT / √RR
RR interval: 0 ms
Normal QTc (male): < 430 ms
Prolonged QTc: > 450 ms
Clinical Interpretation
Enter values to calculate QTc
Arrhythmia Risk Assessment
Example Calculation
Adult Male Patient
Clinical scenario: 45-year-old male on amiodarone therapy
QT interval: 380 ms
Heart rate: 75 bpm (RR = 800 ms)
Patient sex: Male
Calculation (Bazett Formula)
QTc = QT / √RR
QTc = 380 ms / √0.8 s
QTc = 380 / 0.894
QTc = 425 ms
Interpretation: Normal QTc for male (< 430 ms)
QTc Reference Ranges
Males
Females
QTc Correction Formulas
Bazett (Most Common)
QTc = QT / √RR
Fridericia
QTc = QT / ∛RR
Framingham
QTc = QT + 0.154(1-RR)
Hodges
QTc = QT + 1.75(HR-60)
QT Prolonging Factors
Medications
- • Antiarrhythmics (amiodarone, sotalol)
- • Antibiotics (macrolides, quinolones)
- • Antipsychotics
- • Antidepressants
Electrolyte Abnormalities
- • Hypokalemia
- • Hypocalcemia
- • Hypomagnesemia
Conditions
- • Congenital Long QT Syndrome
- • Bradycardia
- • Heart disease
- • Hypothyroidism
Understanding QT Interval and QTc
What is QT Interval?
The QT interval represents the time from the start of ventricular depolarization (Q wave) to the end of ventricular repolarization (end of T wave). It reflects the electrical recovery of the heart's ventricles.
Why Correct for Heart Rate?
- •QT interval varies with heart rate
- •Faster heart rates = shorter QT intervals
- •QTc allows standardized comparison
- •Essential for arrhythmia risk assessment
Clinical Significance
QT prolongation increases the risk of torsades de pointes, a potentially fatal ventricular arrhythmia that can lead to sudden cardiac death.
When to Calculate QTc
- •Before starting QT-prolonging medications
- •Monitoring patients on high-risk drugs
- •Evaluating syncope or palpitations
- •Family history of sudden cardiac death
Medical Disclaimer
This QTc calculator is intended for educational and informational purposes only. It should not be used as a substitute for professional medical advice, diagnosis, or treatment. QT interval measurements must be performed accurately from a 12-lead ECG by qualified healthcare professionals. Clinical decisions regarding QT prolongation, medication adjustments, or cardiac evaluation should always be made by qualified medical professionals. The calculator provides multiple correction formulas for comparison, but clinical interpretation requires consideration of the patient's complete clinical picture, medications, and comorbidities.