Correct the QT interval for heart rate using the Bazett formula to assess TdP risk.
When to use: QTc prolongation is a surrogate marker for risk of Torsades de Pointes (TdP), a potentially fatal ventricular arrhythmia. Evaluate QTc before prescribing QT-prolonging medications (antiarrhythmics, antiemetics, antipsychotics, fluoroquinolones, azithromycin), in hypokalemia/hypomagnesemia, hypothyroidism, and congenital long-QT syndromes. Repeat ECG after initiating or increasing dose of any QT-prolonging drug.
Calculator
Measured from start of QRS to end of T wave
Fill in all fields to see the result
Formula
QTc (Bazett) = QT (ms) / √RR (s)
RR (s) = 60 / HR (bpm)
Key Points for NEET PG
Bazett formula: QTc = QT / √RR — most widely used despite overcorrection at extreme heart rates.
Normal QTc: ≤440 ms in men, ≤460 ms in women; risk threshold for TdP is >500 ms.
Women have intrinsically longer QTc due to lower testosterone — important for drug safety studies.
Preparing for NEET PG? Recollia's AI Tutor explains the clinical reasoning behind every formula — not just the answer, but the why that examiners test.
