Hemodynamics

QTc (Bazett) Calculator

Heart-rate-corrected QT for judging torsades risk with QT-prolonging drugs and low potassium or magnesium; Bazett over-corrects at fast rates.

Reviewed by Alex G, BSN, RN, CEN, CCRN, CMC, NREMT-P · From the Reference tab of the app

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Formula

QT / sqrt(60/HR)

Reference: Normal up to about 470 ms (men) or 480 ms (women)

How it is used

• About 470 ms in men and 480 ms in women is the 99th percentile in healthy adults; over 500 ms is highly abnormal and carries a higher risk of torsades (Drew 2010).
• Bazett runs long at faster rates, especially above about 85/min; Fridericia or Framingham correct better there (Drew 2010).

Management of Prolonged QTc

• Discontinue QT-prolonging medications (e.g., Haldol, Zofran, Amiodarone, fluoroquinolones).
• Replete electrolytes (Maintain K > 4.0 and Mg > 2.0).
• If Torsades occurs, treat with IV Magnesium Sulfate and overdrive pacing.

Same formula as the app. Open it in the web app.

Related one-pagers

• Rhythm GalleryBazett's QTc (QT ÷ √RR, in seconds) overcorrects at fast rates, where Fridericia (QT ÷ cube root of RR) is more accurate. A QTc over 450 ms in men or 460 ms in women is long (AHA/ACCF/HRS 2009; Drew 2010 uses 470 and 480); over 500 ms, or a rise of more than 60 ms, carries high torsades risk (Drew 2010). A wide QRS inflates the QT: trend one lead and method. V1 best separates VT from aberrancy and right from left bundle patterns, and II shows P waves best (Sandau 2017).
• Toxidromes and AntidotesQTc over 500 ms, torsades · Methadone, antipsychotics, citalopram, sotalol · Magnesium, potassium, overdrive pacing
• Behavioral Emergencies, Agitation and AbuseAlcohol intoxication · Antipsychotic; a benzodiazepine adds respiratory depression · Haloperidol 5-10 mg IM, onset 10-20 min (label 2-5 mg); QTc if possible
• ACS and STEMITakotsubo is a form of acquired long QT syndrome (Ghadri 2018): most malignant arrhythmias come with a QTc over 500 ms, as pause-dependent torsades degenerating into VF. Beta-blockers are used cautiously with bradycardia and a QTc over 500 ms, QT-prolonging drugs cautiously in the acute phase, and the ECG is monitored continuously.

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For education and exam preparation only. Follow your institution’s protocols. For education and exam preparation only. Verify results independently and follow your local protocols and medical direction. Not a substitute for clinical judgment.