Bazett Corrected QT Interval (QTc) Calculator
Calculates heart rate-corrected QT interval (QTc) using the Bazett formula (most widely used clinically). Prolonged QTc is associated with risk of Torsades de Pointes and sudden cardiac death.
Score interpretation
QTc within normal male limits (< 440 ms)
→ No specific action required for QTc alone; continue current medications; document baseline QTc; monitor QTc when starting QT-prolonging drugs; counselling if family history of LQTS or sudden cardiac death.
Borderline prolongation in males (440-459 ms)
→ Review QT-prolonging medications (see CredibleMeds list -- antibiotics: azithromycin, clarithromycin, fluoroquinolones; antifungals: fluconazole; antipsychotics: haloperidol, quetiapine; antiemetics: domperidone, ondansetron; antidepressants; antiarrhythmics: amiodarone, sotalol); correct electrolytes (K+ > 4.0, Mg2+ > 0.8 mmol/L); ECG before and 4 hours after QT-prolonging drugs; repeat ECG in 1-2 weeks; if suspected congenital LQTS: genetics referral, beta-blocker, ICD assessment.
Significant QTc prolongation -- risk of Torsades de Pointes
→ Stop all non-essential QT-prolonging medications immediately; correct electrolytes urgently: IV potassium (K+ target > 4.5 mmol/L), IV magnesium (MgSO4 2 g IV bolus if TdP); continuous cardiac monitoring; if TdP occurs: overdrive pacing (100-120 bpm) or IV isoproterenol to shorten QT; do NOT use antiarrhythmics (most worsen QT); defibrillation if TdP degenerates to VF; cardiology review urgently; if congenital LQTS suspected: mexiletine may help (LQT3); beta-blocker for LQT1/2; left cardiac sympathetic denervation if refractory; ICD if high-risk congenital LQTS or recurrent TdP.
Interpretation bands for the Bazett QTc. Apply clinical judgement and local guidance.
References
- Bazett HC. An analysis of the time-relations of electrocardiograms. Heart. 1920;7:353-370.
- Priori SG et al. 2015 ESC Guidelines for the management of patients with ventricular arrhythmias and the prevention of sudden cardiac death. Eur Heart J. 2015;36(41):2793-2867.
Related
Curated clinical cross-links plus same-class fallbacks.
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- Hypertensive Emergency · ESC/ESH 2018 Hypertension Guidelines; NICE NG136
- Bradycardia Management · Resuscitation Council UK ABCDE; ESC 2021 Pacing Guidelines
- Ventricular Tachycardia / Fibrillation · Resuscitation Council UK ACLS; ESC 2022 Ventricular Arrhythmia Guidelines
Featured in these MRCEM clinical pathways
The Bazett QTc is covered in detail — with RCEM/NICE evidence base, indications and pitfalls — in the following exam-focused pathways on our sister siteReviseMRCEM.
MRCEM Primary / Intermediate / OSCE candidates: each pathway includes exam-style questions, RCEM/NICE citations, and FAQ summaries.
Decision support only — verify against a current formulary, NICE, or your local guideline before clinical use.