QTc Interval Calculator (Bazett & Fridericia)
Correct the QT interval for heart rate using both Bazett and Fridericia formulas to assess risk of drug-induced QT prolongation and Torsades de Pointes.
Results
What is it?
For educational and clinical reference only. Not a substitute for professional medical judgment. Always verify with current clinical guidelines and consult qualified healthcare providers. QTc is the heart-rate-corrected QT interval. The Bazett formula (QTc = QT/vRR) is most widely used but overestimates at high heart rates. Fridericia (QTc = QT/?RR) is more accurate across heart rates. Normal QTc: <440 ms (men), <450 ms (women). QTc >500 ms is associated with high risk of Torsades de Pointes (TdP).
How to use
Measure the QT interval from the start of the QRS to the end of the T-wave in ms (use lead II or V5). Calculate the RR interval as 60,000 � heart rate (bpm). Enter both values to get QTc by both formulas.
Example scenario
QT = 420 ms, HR = 60 bpm ? RR = 1000 ms. Bazett: 420/v1 = 420 ms (normal). HR = 100 bpm ? RR = 600 ms. Bazett: 420/v0.6 = 542 ms (high risk � same QT but tachycardic patient has much higher corrected QT).
Pro tip
Many common drugs prolong QTc: antipsychotics (haloperidol, quetiapine), antibiotics (azithromycin, fluoroquinolones), antifungals (fluconazole), antiemetics (ondansetron), and methadone. Check CredibleMeds (www.crediblemeds.org) for comprehensive QT risk classifications. Always assess electrolytes (K+, Mg�+) as hypokalemia and hypomagnesemia potentiate QT prolongation.