نظرة سريرية عامة

Corrected QT interval is a bedside decision-support calculation used to standardize a defined part of clinical assessment. It adjusts the measured QT interval for heart rate and displays three established corrections because no single equation performs best at every rate. The result should be interpreted with the patient’s presentation, baseline function, serial observations, laboratory method, medication exposure, and the protocol used by the treating institution. It is an aid to communication and risk stratification rather than an independent diagnosis or treatment order.

Enter contemporaneous values and confirm every unit before calculating. When physiology is changing, repeat assessment and prioritize the clinical trajectory over a single number. Document the input values alongside the result so another clinician can reproduce the calculation and recognize assumptions. Thresholds describe populations and do not remove the need to investigate discordant symptoms, examination findings, imaging, or biomarkers.

دواعي الاستخدام

• Manual confirmation of QT correction when QT and heart rate are known
• Review of medications or conditions associated with repolarization delay

القيود والسلامة

Thresholds vary by sex and context; wide QRS, bundle-branch block, pacing, U waves, and atrial fibrillation require specialized measurement or adjustment. Validation cohorts, case mix, prevalence, and treatment era affect observed event rates. Pregnancy, extremes of age or body composition, critical illness, and major comorbidity may reduce transportability unless specifically represented in the original model. Do not extrapolate beyond the stated population or substitute this estimate for a validated local pathway.

Before acting, check for missing data, measurement error, competing diagnoses, contraindications, and time-sensitive emergencies. A low-risk label never overrides clinician concern; a high-risk label does not prove the target condition. Discuss consequential decisions with the appropriate senior or specialty team and use current regional guidance.

• Automated or formula estimates may be unreliable in irregular rhythm, paced rhythm, or wide QRS
• Bazett overcorrects at high heart rates and undercorrects at low rates

المعادلة

Bazett QTc = QT/√RR; Fridericia QTc = QT/∛RR; Framingham QTc = QT + 0.154(1 − RR), with QT and RR in seconds

تفسير النتائج

• Often <450 ms male / <460 ms female — Typical reference range: Lower repolarization-risk signal. Interpret with ECG morphology and clinical context.
• Approximately 450–499 ms — Borderline or prolonged: Risk depends on sex, drugs, electrolytes, and symptoms. Verify manually and correct reversible factors.
• ≥500 ms — Marked prolongation: Higher torsades risk. Urgent medication/electrolyte review and monitoring assessment.

المراجع

1. Vandenberk B, et al. Which QT Correction Formulae to Use for QT Monitoring? JAHA. 2016.
2. Rautaharju PM, et al. AHA/ACCF/HRS recommendations for ECG standardization.

الأسئلة الشائعة

Which formula should I use?

Fridericia or Framingham often performs better away from 60 bpm; Bazett remains common but is rate-sensitive.

How should QT be measured?

Use a clear lead, measure from QRS onset to T-wave end, average representative beats, and exclude rather than include a separate U wave.

Does QTc above 500 ms guarantee torsades?

No, but it is an important risk marker that warrants prompt review of reversible causes and monitoring needs.